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How ADAS Works in the Winter

ADAS in WInter

With winter getting uncomfortably close, let’s grab a hot beverage and examine a topic that is sure to cause headaches this season: ADASequipped vehicles and winter driving.

 

ADAS and Winter

ADAS is short for “Advanced Driver Assistance System. Each manufacturer has its own name for the suite of functions that make up its ADAS. Honda calls it “Honda Sensing, Cadillac calls it “Super Cruise,” and Tesla“Autopilot. Essentially, ADAS covers a whole slew of system operations that make a car capable of performing a set of functions by itself, or without a human doing 100% of the operation. There is a spectrum of functions, ranging from simple warning when someone is in your blind spot, to literally steering and braking for you. These systems are finicky at best and have operational quirks even in ideal conditions. Let’s talk a bit about ADAS and some considerations when using (or attempting to use) it in the winter. 

Since I am a Honda man, I am going to focus on the Honda Sensing suite. It’s a pretty good system with basic nuts and bolts that you can use to try to intuit operation on other vehicles. One of the biggest hurdles in these systems is decoding the long list of acronyms. Here are a few: 

 

 

The Honda Sensing Suite

Forward Collision Warning is FCW, Lane Departure Warning is LDW, Lane Keeping Assist is LKAS, Blind Spot Information is BCM, etcHonda keeps it pretty clean with their acronyms and the function is relatively intuitiveTake Collision Mitigating Braking system, for example, it sounds like it will warn you of an impending collision and possibly apply the brakes for you if there is no intervention. This is indeed what the system does. Lane Keeping Assist sounds like it might steer the vehicle back into your lane when you wander out of it, and that is indeed what it does. 

Most of these systems are made possible due to two new hardware. There is a camera mounted in the windshield and a millimeter-wave radar mounted behind the front grille. 

ADAS Honda Camera & Radar

 

These two components work in tandem with the traction control and electric power steering systems to monitor and warn if necessary, making driving a car a more mindless experience. 

To put it generically, radar is used for detecting solid objects whether they are in motion, standing still, or in a non-linear trajectory in comparison with the vehicle’s own. The camera also detects objects, but besides solid objects, it detects lane markings and speed limit signsIf either of these two components come up with the calculation that you are drifting in your lane or coming up hot on a car or pedestrianthey initiate the traction control system and/or power steering system to intervene. 

ADAS Lane Control

Lane control uses the front camera only, as it must detect road markings that the radar cannot see. 

ADAS Collision Warning

 

 

Lane Assist and Auto Braking

I can tell you that the LKAS’s (Lane Keeping Assist) opinion of what being in my lane means, and my opinion, sometimes differ significantly. I will notice the warning chime, and the nudge of the wheel regularly when I feel like I am being attentive and aware of my lane position. The LKAS, when allowed to have its druthers, likes to wander from line to line, picking which one it can see the best. 

I will also say that the CMBS (Collison Mitigating Brakes) can sometimes choose to sound the alarm when I am coming to a very reasonable stopon the flip side, it can be radio silent when I am coming up fast on someone’s bumper. I never forced it to activate when I was doing pre-delivery inspections at the dealer, but I get it to activate from time to time during normal driving. 

This is a learning system, and it will get a bit better as it learns a driving style, but even under ideal conditions, there are glitches and hiccups in operation. So, what happens when snow is covering the road? When salt is packed up on the radar? Does this system stand a chance of operating well on an icy road with unclear markings? I don’t know how many of you have driven in a blizzard, but you can hardly see anything, let alone which lane you’re in.  

 

ADAS System Caveats and Glitches

Honda and every other OE have a long list of system caveats for weather and road conditions. Consult with the manual for all the details, but usually, the list goes a bit like this. 

 

Environmental conditions: 

  • Driving in bad weather (rain, fog, snow, etc.) 
  • Sudden changes between light and dark, such as an entrance or exit of a tunnel 
  • There is little contrast between objects and the background   
  • Driving into low sunlight (e.g. at dawn or dusk) 
  • Strong light is reflected onto the roadway 
  • Driving in the shadow of buildings, trees, etc. 
  • Roadway objects or structures are misinterpreted as vehicles and pedestrians 
  • Reflections on the interior of the windshield 
  • Driving at night or in a dark condition such as a tunnel 

Roadway conditions: 

  • Driving on a snowy or wet roadway (obscured lane markings, vehicle tracks, reflected lights, road spray, high contrast) 
  • The road is hilly, or the vehicle is approaching the crest of a hill 
  • Driving on a curvy, winding, or undulating road 

Vehicle conditions: 

  • Headlight lenses are dirty, or headlights are not properly adjusted 
  • The outside of the windshield is blocked by dirt, mud, leaves, wet snow, etc. 
  • The inside of the windshield is fogged 
  • An abnormal tire or wheel condition (wrong-sized, varied size or construction, improperly inflated, compact spare tire, etc.) 
  • When tire chains are installed 
  • The vehicle is tilted due to a heavy load or suspension modification 
  • The camera temperature gets too high 
  • Driving with the parking brake applied 
  • When the radar sensor in the front grille gets dirty 

 

If any of the conditions for the road and vehicle are on the list, you can expect erratic or possibly no function from part of, or all the ADAS system. This is just the list from the CMBS section of the owner’s manual and does not include pedestrian notesTesla even warns you about kangaroos. The point is to show how limited these systems still arethey may seem like miraculous bits of hardware and software, but they are still far from perfect. 

ADAS LKAS malfunction

These are some of the conditions involving just road markings on clean roads that you may have LKAS malfunction.

ADAS Odometer

 

Quick ADAS Fixes

Some vehicles will literally tell you to go clean off the radar area of the front grilleThis happens very frequently and you may have to stop and do this several times on a single drive in some cases. So when a customer comes in complaining about operation during the snowy months, make sure to educate them. Wipe off the windshield and the front grille, and advise they wait until the roads are clear and dry before they try to engage ADAS on their commute. Better advice yet would be to retire the systems between November and March and break them out again the same time you dust off the lawnmower. 

 

And if want to talk me to about any Honda in your shop, I’m available to call as part of our Virtual Tech team – 1.800.288.6210 

 

All images courtesy of Honda


How to Service Air Conditioners on Hybrid Vehicles

Service Hybrid Vehicle's A/C

 

First Things First

It is very important to recognize the differences between conventional and electric compressor A/C systems, obtain the proper training, the required equipment, and use the specified refrigerant oils to ensure the complete, safe, and quality repairs to these A/C systems.

 

Hybrid Vehicle A/C Compressors

Hybrid Electric Vehicles Electric A/C compressors use the high voltage from the hybrid battery pack to operate the compressor. The high voltage DC from the battery pack is converted to 3 phase AC voltage to operate the motor inside the A/C compressor. Sometimes the inverter/converter module is inside the compressor, fed by 2 high voltage wires, and sometimes it is outside the compressor, feed by 3 high voltage wires.

 

How to Stay Safe Servicing Hybrid Vehicle A/C Systems

DO NOT attempt to service a hybrid vehicle A/C system without getting the proper training first! Knowing what can kill you and what personal protective equipment to use to prevent that is important. Orange cables going to the compressor indicates you will need High Voltage gloves and a CAT III 1000 Voltmeter to prove the system is disabled before disassembling.

Be sure to read our article about safely diagnosing and working on hybrids.

 

Hybrid A/C System’s Refrigerant Oil

Electric compressors require non-conductive Polyol Ester (POE) refrigerant oil. There are several manufacturers of POE oils, they are not the same. Only use the manufactures specified refrigerant oil. It is also recommended to use a separate machine and flush the lines between vehicles to prevent oil contamination.

A PAG oil contamination of 1% can reduce the insulating property from 10 Megaohms to under 1 megaohm, potentially setting isolation fault codes.

Leak detection die should NOT be used in systems with electric compressors. UV dies most often contain PAG oil and/or solvents. PAG oils reduce the insolation properties of the oil and solvents are flammable.

Most manufactures require a complete system/all components replacement for contamination.

Recovery/ recycling/ recharge (RRR) machines that meet SAE specification J2788H are acceptable for use on hybrid vehicles with electrically driven compressors. These RRR machines are designed to prevent a harmful amount of oil from mixing with the refrigerant during charging.

 

A Few Other Notes

Sun load sensors do make a difference in operational characteristics. If you are diagnosing a performance complaint, you will want to test the system outside with a strong sun load.

The “ECON” button also makes a large difference in the operational characteristics. The acceptable outlet temperature with “ECON” on can be 10 to 20 degrees higher than in “MAX A/C”.

 

Some Tools You’ll Need for Diagnosis

You will need to have Bidirectional control and complete data PIDs to diagnose a Hybrid Vehicle’s A/C performance issues. Electrically powered compressors vary compressor RPM to modulate the compressor volume. The pressures on a gauge set will look the same as other R134 systems; high 20’s to low 30’s on the low-pressure side and 200 to 300 on the high side.

Finally, you’ll also need a good repair information source.

 

Further Learning

Now that you’ve got the basics you can start diving more into the world of Hybrid Vehicle A/C systems. Check out these resources below for additional learning and training.

www.macsw.org 

www.Fueleconomy.gov 

www.greencarcongress.com 

www.edmunds.com/ford/escape-hybrid/2010/ 

www.hybridcars.com 

www.sae.org/events/aars/presentations/2004-ishikawa.pdf 

www.nrdc.org/energy/vehicles/hybrid.asp 


Think Backwards When Working on Electronic Parking Brakes

Servicing Rear Brakes On Cars with Electronic Braking Systems

 

Today I would like to sharpen your minds about something that comes up quite often in our line of work. Rear brake pads, and more specifically, how to service them when there’s an electronic parking brake system on the vehicle.

The genesis of the idea for this article came from a Virtual Tech call I took on a 2018 Honda Accord. A sharp young tech wanted to do a rear pad slap on this vehicle and he wanted to know how to do it. The service manual was only of moderate help and he had additional questions. Turns out, so did I. So if you like hucking brake pads, have a seat and rub your brain against this whetstone.

 

Psst. There’s a free cheat sheet at the end of this article too

 

 

Quick Parking Brake Explanation

 

Electronic parking brakes have been around for quite a while now, and like skinning a cat, there are many different ways of accomplishing the same thing. Some manufacturers designed a cable that gets pulled on by a motor, but most companies put a small DC motor on the back of the brake caliper. As it’s the most common design, this is the style we’re covering today.

 

Electronic parking brake systems usually consists of 3 main components

 

  1. A control module of some sort. Sometimes this is the same unit that does the thinking or work for traction control and ABS, and sometimes it’s a bespoke unit just for the parking brake.
  2. A switch, to communicate the intent of the driver to engage or disengage the parking brake.
  3. Parking brake actuators. These are electronically-controlled calipers, and every system I’ve ever seen are on the rear of the vehicle. Sometimes they’re combined with the base brakes, sometimes they’re their own little sub caliper. Tesla comes to mind.

 

How Electronic Parking Brakes Operate

 

Now that we have an idea of the components, let’s talk about operation. Some manufacturers use the electronic parking brake every time the vehicle is shut off in park. Others use the parking brake only after a prescribed number of miles, to keep the caliper exercised. And still others use the parking brake as a hill-start assist, or as a brake-hold function every time the vehicle comes to a stop. Do a little research on the system you’re dealing with and try to get an idea about when you can expect the parking brake to be engaged.

My basic rule of thumb is to assume it’s always engaged unless you’re trucking down the road. We don’t know when the traction control module might want to turn on the parking brake, thus “always” seems as good a time as any.

Now let’s dive into the specifics.

 

2018 Honda Accord Electronic Parking Brake Components

 

The parking brake switch: pull up to apply, push down to release.

 

 

There are electric actuators mounted on the backs of both rear calipers—they have only 2 wires, one for power, one for ground. The Vehicle Stability Assist (VSA) module reverses polarity to engage or disengage the actuator. The VSA module judges the application based on how much amperage the actuator takes, very little amperage means the brakes are not applied, a lot of amperage means the pads are applied.

 

The Vehicle Stability Assist (VSA) Control Unit is in charge of the whole thing—the parking brake switch wires go right into it and the wires for the actuators come right out of it.

Now that I know the players, it’s time to get to know the game.

 

When does a 2018 Honda Accord engage the parking brake?

 

When the customer requests it, using the parking brake switch. Pull up to engage, push down to disengage.

Every 1,864 miles, if the parking brake has not been engaged, this is to exercise the calipers and compensate for brake pad wear.

Every time the ignition is turned off, depending on customer’s preference/settings.

When the Vehicle Stability Assist (VSA) system determines it requires increased braking effort in an emergency.

When the VSA system determines it’s unable to hydraulically apply pressure to the rear brakes during an ABS or traction event.

During automatic brake hold, if brake hold exceeds 10 minutes.

 

When does a 2018 Honda Accord disengage the parking brake?

 

Drive-away. Essentially, you start to drive with the parking brake engaged it will automatically disengage for you. How thoughtful.

Maintenance Mode. This is a service function you need to command with a scan tool, more on this later. The VSA module is supposed to retract the electric parking brake piston in this mode.

“Neutral Position Holding Mode.” This is a mode that allows the parking brake to be released for 15 minutes and is usually used for car washes, not pad slaps. Unless of course you’re the fastest slapper in the west!

“Temporary Cancel of Automatic Electric Parking Brake Mode.” Despite this mode saying “temporary” and the other one saying “holding” this mode releases the parking brake for much longer than the usual 15 minutes.

 

What does Honda have to say about servicing the rear brake pads?

 

Steps 1-3 are boilerplate nonsense: check the brake fluid, take off the tires, the standard steps. Step 4 is “enter maintenance mode.” This is huge. Supposedly, the scan tool is to retract the parking brake actuator piston, which it usually does. But when it’s time to exit maintenance mode you may run into a problem. It’s been my experience that the aftermarket scan tools can put the system into maintenance mode, but they seem to have a hard time taking it back out. Typically, you end up with limited throttle, all kinds of codes, and possibly limp-in transmission function. More often than not this ends up with a trip to the dealer on the back of a tow truck. My personal advice? Don’t let the system know you’re servicing brake pads.

In Step 4, Honda provides a note: you can manually remove the parking brake actuator and using a TORX socket, you can turn the actuator spindle clockwise until it stops. This will be a full retraction of the parking brake piston, but without using the actuator to do it. Before you do this, you’ll want to ensure the parking brake is not engaged—the manual says nothing about this. Put the system into “Temporary Cancellation Mode.” Put the vehicle in park with the ignition on, then turn the ignition off and within 2 seconds press the electric parking brake switch down. This should cancel the parking brake function until the next ignition cycle.

Here’s another look at the caliper with the actuator off. Note: both sides say to spin the spindle clockwise to disengage the piston.

Before you twist any spindles, get a clean sheet of paper and make some notes. How many turns does it take counterclockwise to fully engage the pads to the rotor? Just go until you feel some pressure and you can’t turn the rotor anymore. Count the turns and back it out to where it was originally. This is what I call “home position.” This is how far away the actuator prefers the piston is from engaging the pads. We’ll aim for this when we put new pads in. That way the actuator will be none the wiser.

Go ahead and back out the electronic parking brake piston fully, clockwise until it stops. Then service the rear brake pads as usual. Remove the caliper, press the hydraulic piston back in however you want—C-clamp, piston tool, by hand if you’re inclined. Clean up the slides and hardware, out with the old, in with the new pads, hang the caliper back on.

 

Now what?

 

We have a caliper with 2 pistons retracted! The service manual doesn’t provide insight and we’re in a pickle. My solution? Think backwards. We have our caliper installed, and before that? You pushed that hydraulic piston back in. Know of a good way to push it back out? Jam on the brake pedal until it’s nice and firm. Don’t turn on the ignition. You’ll ruin your time without the parking brake operating—remember that “Temporary Cancellation Mode”?

Now we have our calipers hydraulically seated again. Recall when you turned the parking brake spindle clockwise? Go ahead and turn it counterclockwise. Do it until you get pressure and the rotor is locked up, then back it off the number of turns to that “home position” you recorded earlier. Maybe it’s a full turn, half turn, two turns—it’s going to be a bit different on every car. Put the parking brake actuators back onto the calipers.

 

Wrapping Up and A Free Cheat Sheet

 

So the pads are installed, the pistons (both hydraulic and electronic) are where they were before you touched anything, and the parking brake actuators are on. Go ahead and ignition on, turn the parking brake on and off a couple times, see that the parking brake indicator is functioning, and you have no codes.

Congratulations! You’re free and clear. I’ve created a cheat sheet about electronic parking brake service, so please download it and hang it up on your box. If you run into anything strange while working with one of these systems, or one fails and that’s why you’re touching it, give us a call at the Hotline and we will help you get it squared away. Happy wrenching!

 

Download the Electronic Parking Brake Service Cheat Sheet

 

 


Meet L1 Master Technician Dan Larson

 

His Credentials

AAS Degree, ASE Master Technician, ASE Certified

 

Dan’s Start in Auto Repair

Dan’s professional journey started when he completed his Automotive Technician AAS Degree at St. Cloud Technical College, Saint Cloud MN in 2009.

 

Dan’s Career Before Identifix

After graduation, he started working at a local Minneapolis/St. Paul independent repair shop, JPT Services. Dan worked closely the shop owner, a longtime industry veteran who taught Dan most of the knowledge an skills that he carries with him today.

Dan eventually left that shop in search of new opportunities and landed at Certified Auto Repair. Originally hired as the Lead Technician, Dan also took on the role of Shop Foreman. During this time he also helped write content for automotive websites and helped create a custom vehicle inspection app for repair shops.

 

Joining Identifix

After 6 years with Certified, Auto Dan was ready for a new challenge. So he called it quits at the shop and joined the Virtual Tech team at Identifix in June of 2017. Since then, Dan has been helping countless techs across the country to repair their shop’s toughest vehicles.

 

When He’s Not Working

In his free time, Dan enjoys spending time with his family, traveling, biking, skateboarding, snowboarding, and just about any other outdoor sports or activity you can think of.

 


Fix of The Week 8/17/19

 

Fix of The Week

Every week we’re posting our favorite head-scratchers and interesting mechanical issues submitted by our Direct-Hit customers.

For a chance to have something you’ve worked on appear as a Fix of the Week, and win a cool little prize for your shop, all you have to do is post your unique fixes in Direct-Hit. Just look up the vehicle you’re working on, click on Post Fix at the top right, then tell us the problem and what you did to fix it.

 

This Week’s Winners

On this edition of Fix of The Week: A Subaru with a lack of power and two Hondas with cruise issues.

 

2006 Subaru Outback – Black Rock Auto

This Subaru had a lack of power and no fault codes. The engine oil level was low but still registered on the dipstick. I verified lack of power on the test drive, noted the low engine oil activity, and verified there were no codes. Data showed that the fuel trim was correct, but using a 5-gas analyzer at the tailpipe showed a lambda value of 1.185 and CO2 at 13.0% with O2 at 3%. I tested the fuel and found 10% alcohol content OK.

I solved the issue by topping up the motor oil and observing 5-gas at the tailpipe. I saw the CO2 climb to 15.4% and O2 drop to 0.1%. Power was restored—it was due to the cam phasers not filling up and affecting the valve position, which caused the engine breathing problems. The ECM doesn’t recognize this and doesn’t set codes so top off the oil and the problem solved.

 

2016 Honda Civic – Accountable Automotive

This vehicle had no cruise nor adaptive cruise, and the cruise main would turn on but wouldn’t set. The system stopped working for the customer suddenly, and they confirmed no debris ever hit the vehicle to knock out radar and they hadn’t recently replaced the windshield. The dealer had recommended replacing all cruise components, about $6,000-$8,000 worth of work—they had no idea.

The vehicle didn’t have any codes but did have some history of U, VSA, and steering history codes. All inputs were good: brake pedal, accelerator, radar, camera, yaw, main switch, set, decel, resume, PRNDL, VSA. Lane departure, collision avoidance, VSA features were all operating properly.

We cleared all codes—none returned, still inoperable. We didn’t find any wiring or connector faults. We just so happened to have a ’16 Civic to compare inputs with and view some identical data.

I disconnected the battery and jumpered across terminals for 20 minutes. On reconnect, the system went into an “initialization mode.” All driver integration modes were disabled and “tells” on the cluster (LKASS, VSA, collision avoidance, ACC) instruct you to drive carefully while initialization is in process. I drove until all the lights went out, about 3 minutes, and the cruise and adaptive cruise were back to operational.

 

2002 Honda Accord – Lester Gutierrez

This vehicle’s cruise control was inoperable and the main switch indicator light was off at all times. I checked fuse 6 driver’s under the dash fuse box. I resistance tested the cruise control main switch and found both bulbs in the circuit open. I replaced the blubs and conducted a cruise control unit input test. The cavity 2 gray wire had no power when the brake pedal was released. I test drove the vehicle and the cruise set above 25 MPH—the indicator lights on the cruise control main switch and cruise control light on the dash were working as required.

 

FIND THESE AND 2 MILLION OTHER CONFIRMED FIXES IN DIRECT-HIT. TRY IT FOR 14 DAYS FOR JUST $1.00!

 


Fix of The Week 8/9/19

 

Fix of The Week

Every week we’re posting our favorite head-scratchers and interesting mechanical issues submitted by our Direct-Hit customers.

For a chance to have something you’ve worked on appear as a Fix of the Week, and win a cool little prize for your shop, all you have to do is post your unique fixes in Direct-Hit. Just look up the vehicle you’re working on, click on Post Fix at the top right, then tell us the problem and what you did to fix it.

 

This Week’s Winners

On this edition of Fix of The Weektwo Cadillacs — one with a running board issue and another with cluster problems—and a Toyota with a bad shake.

 

2016 Cadillac Escalade ESV – Highland Transmissions

This vehicle’s driver side running board would not retract. I attempted to retract from ¾ open and found that if hand pressure was applied to the running board it would retract when the door was closed. I checked for any restrictions and found none. I cleaned the hinges, sprayed with worth film and it works fine. I sprayed the passenger side as well. 

 

2017 Toyota Corolla – Rogers Automotive

The customer came in complaining of shake on acceleration from the front passenger side. 

When I test drove it, it felt like a bad axle so I replaced it with the Toyota part and it was betterbut still had a constant shaking happening. I balanced the tires and found 2 bent rims. I replaced 2 rims and new set of good tires road forced balanced. The next day still noticed the shaking and couldn’t find anything. The front end was tight, the wheel bearing felt good and there was no noise. The customer was told by a tech at Toyota that a wheel bearing is common on this car so replaced the wheel bearing per customer request and the problem was gone.   

 

1998 Cadillac DeVille – ASAP Auto Repair

This vehicle’s digital part of the cluster would not light uponly the indicator lights worked. No codes present and powers and grounds were good at the cluster. I replaced with a used cluster and had to use resistors to find out which that used cluster was programmed with. Tried about 15 different combinations—try one, wait until 3-minute lockout and move on to the next resistor value until the car starts.

 

Find these and 2 million other confirmed fixes in Direct-Hit. Start Your 14-Day Trial

 

 


Fix of The Week 7/4/19

 

Fix of The Week

Every week we’re posting our favorite head-scratchers and interesting mechanical issues submitted by our Direct-Hit customers.

For a chance to have something you’ve worked on appear as a Fix of the Week, and win a cool little prize for your shop, all you have to do is post your unique fixes in Direct-Hit. Just look up the vehicle you’re working on, click on Post Fix at the top right, then tell us the problem and what you did to fix it.

 

This Week’s Winners

On this edition of Fix of The Weeka Kia with no acceleration, and separate battery and fueling problems in two Volvos.

 

2014 Kia Forte – AT Repair Inc.

The customer stated that the “engine” light would come on and the car wouldn’t accelerate. We performed a scan test and found service code P2138. We tested the pedal sensor and throttle body and found an intermittent erratic signal from the pedal sensor. We replaced the accelerator pedal which resolved the issue. 

 

2013 Volvo XC60 – Boulevard Autoworks

This vehicle’s rear hatch would go partway up and then stop—you had to manually open and close the door. We checked the scan tool data and watched for switch inputs and outputs. One PID in the data was the reason why the last operation was unsuccessful. The PID said low battery voltage. We did a starting and charging check, which the battery failed. We also noticed the rear gate would work fine with the vehicle running. We replaced the battery and everything worked properly.   

 

2010 Volvo S40 – Classic Automotive Repair

The customer complained that the vehicle pump would shut off when refueling. They had to go very slow to get refuel and it took a long time. We checked and no codes were set for evap issues, no hard restart and the leak detection pump passed the test. We visually inspected the filler pipe and those hoses passed.

We pulled the vent line from the tank to canister, the 3 piece hose, and the small section of the hose from tank to Y fitting was collapsed internally. We replaced the vent line assembly from the tank to the canister and that solved the issue.

 

Find these and 2 million other confirmed fixes in Direct-Hit. Get $40 off your first three months.

 

 


Defeating the Air Conditioning Bogeyman

 

A/C Pressure and Temperature

 

Automotive repair professionals have a lot of “Bogeymen” we have to deal with. There’s the Bogeyman who makes electrical circuits function. There’s the Bogeyman involved with CAN communication. We have a Bogeyman for A/C too. In nearly every system that works but you’re just not sure why it works, theres a Bogeyman involved. I like to try to shoo away the Bogeyman, or maybe shine a light on him so readers can see he’s not so scary after all. Then we can get back to work with some understanding and some peace from the monsters. 

Today, we are shining the flashlight at the A/C Bogeyman. Remember learning about A/C in tech school? Remember hearing big words like Thermodynamics? School is back in session.

 

Air Conditioning Components

 

We’re gonna start with some light lifting. All A/C systems have much in common. They all have very similar parts and they all have two sides where pressure and temperature work their magic together. Check out this diagram showing some basic components and also the state of the refrigerant pressure/temperature between the “high side” and “low side.  

Let’s talk components. They should change the phrase “there are a lot of ways to skin a cat” to “there are a lot of ways to compress a gaseous refrigerant, condense it to a high-pressure liquid, and throttle it to a low-pressure liquid to boil and remove heat from a heat sink. Were not going to get granular and talk about how each type of compressor works, just that they compress. We are also staying away from control devices, like sensors and switches.  

Compressor: This is usually a beltdriven pump; its job is to pull refrigerant in and compress it into a high-pressure vapor. It may have an electromagnetic clutch to engage or disengage it, or it may have a spill valve to control flow. On hybrid/EV vehicles this will likely be driven by an electric motor instead of a belt. 

Condenser: This is a big finned heat exchanger, usually mounted right in front of the radiator. This is where the high-pressure vapor goes right after the compressor. Air passes through the fins to cool and condense the high-pressure vapor and turn it into a high-pressure liquid. Air is either motivated by cooling fans, or by ram air as the vehicle is driving. 

Receiver/Dryer: This is a reservoir for the high-pressure liquid. It stores and filters the refrigerant and also has a desiccant to remove water from the refrigerant. This unit is typically mounted in the condenser.  

Thermal Expansion Valve or Fixed Orifice: This is where the refrigerant goes when it is compressed, filtered, and condensed. This is a small orifice that the high-pressure liquid is pushed through, turning it into a low-pressure liquid. Think of it like a can of spray paint. There is high-pressure liquid inside the can, the nozzle at the top is the TXVwhen you press down, the high-pressure liquid sprays out as a low-pressure liquid. If you’ve ever spray painted your hand you know the paint coming out is colder than the can. Thermal Expansion Valves (also called TXV, or just Expansion Valves) respond to the need for refrigerant by varying the size of the opening based on the temperature of the evaporator where the valve mounts.

 

See here a diagram of a TXV. The sensing bulb is full of a gas that expands when warm and presses down on the diaphragm in the valve. This pushes the valve open and allows more high-pressure liquid to spray into the evaporator as a low-pressure liquid, increasing the cooling capacity. Then as the evaporator cools, the gas from the sensing bulb contracts and the valve is allowed to close. Newer TXVs have all this integrated into a single block, you can’t see the sensing bulb anymore, but they function the same. 

A Fixed Orifice performs the same job as a TXV, but does not vary in size at all, the manufacturer simply decides what a good size would be for most situations and lets it ride. A Fixed Orifice can be anywhere in the line between the condenser and the evaporator (hunt for it in the service information). 

Evaporator Core: This is the heat sink inside the vehicle. The low-pressure liquid is sprayed from the TXV or Fixed Orifice into the evaporator. Here it evaporates! It turns into a low-pressure vapor again. Since the refrigerant is not under pressure it boils into a gas. It’s that pressure decrease that puts the “brrr!” in the A/C system. 

Lines and Hoses: These are the conduits that take refrigerant in its varying states to where it needs to bethese should offer no resistance to flow at all, they’re simply tubes that should flow freely. 

 

How the Components of an A/C System Function

 

Now that we understand what each component’s job is, let’s talk a bit about why theyre doing what theyre doing. This whole system is designed to take advantage of one thing: the pressure/temperature relationship of refrigerant. We are going to use R-134a refrigerant as our exampleits still the most commonly used refrigerant, and the new fangled R1234yf has a pretty similar pressure/temp profile.  

The refrigerant cycle can be described as having two parts, the high side and the low side. The highpressure side is the path of the refrigerant after the compressor. It includes the compressor, condenser, dryer, lines, and technically a part of the TXV. The high-pressure side is where all the hot stuff is. The low-pressure side is the other part of the TXV, the evaporator core, and the line going back into the compressor. The low-side is where all the cold stuff is. 

Download and print the pressure/temp chart at the bottom of this article for a reference. You can see that at 68°the refrigerant is essentially 68 PSI. This means on a 68°day you will see about 68 PSI of static pressure in the systemstatic pressure is when the refrigerant has equalized so both the high side and the low side are the same pressure.  

Now if you were to squeeze that 68 PSI until it gets to about 270 PSI (paging Dr. Compressor!) then you’ll see that the temperature raises to about 152°F. The compressor is literally jamming more molecules of refrigerant into a smaller areathey ping around and create heat. I don’t care what you’re squeezing, everything gets warmer when it is compressed. Things that are a gas at ambient temp/atmospheric pressure have a more useful range of pressures and temperatures that we can exploit. 

The Refrigerant Cycle

So we have some hot gas, time to pull some of that heat out via the condenser to turn it into a high-pressure liquid. Leaving the condenser you will have maybe 130° high-pressure liquid, putting us at about 200 PSI. This is our high side pressure. The 200 PSI liquid jams up against the TXVRemember that spray paint can? Here it is throttled down to about 30 PSIchecking the chart it looks like 30 PSI translates into about 34°F. That’s some chilly air! From here the low-pressure gas is pulled back into the compressor via the suction (low-side) line to start the process all over. 

A quick note about condensersthey should only drop about 15-35 degrees of temp across them. If you see 50 degrees drop it’s not because the condenser is doing a really good job removing heatmore likely the condenser is clogged. Either the clog is acting like another expansion valve or the refrigerant is spending way too long in the condenser. 

Congratulations, you just mastered thermodynamics! You understand the components of the A/C system and the refrigerant cycle!  

So, how do we use the pressure and temperatures to fix cars? Let’s keep going to find out.

 

A/C Pressure Diagnostics 

 

Static Pressure: This is always the first step in diagnosing an A/C cooling complaint. Check the ambient air temp, refer to the pressure/temp chart, check the pressure. If the pressure is low, you have low refrigerant chargeevacuate and recharge the system. If the pressure is high you have a non-condensable gas like nitrogen or oxygen in there or a drastic overchargeevacuate and recharge the system. Basically, if you are ever in question about how much refrigerant is in the system, or what is in the system, evacuate and recharge, start fresh. Refer to the service manual for refrigerant type and capacity. 

Normal Operation: High side is usually at least double of what static pressure was, plus 100 PSI if it’s humid. So at 68 PSI your rule-of-thumb pressure range would be 140-240 PSI. 

Low side is usually 30-40 PSI, unless it is very hotthen it might be higher until the evaporator can maintain a colder temp. Off idle on a TXVstyle vehicle, you will see the pressure drop and get as low as 10 PSI. A Fixed Orifice will usually keep the low side steady between 30-40 PSI regardless of RPM. 

High Side Too High, Low Side Normal: If the high side approaches 350-400 PSI then the condenser is unable to rid itself of enough heat to turn the high-pressure gas to a liquid. Make sure the fins are not obstructed. Make sure the cooling fans come on and blow towards the engine. Fans that blow backward will push heat from the radiator and the engine into the condenser, rather than cooling the condenser down. 

Low Side Too Low, High Side Normal: If the low side is too low then the compressor is pulling on the suction side but there is not enough refrigerant flow to feed it. There is either an obstruction in the evaporator, the suction line, or the TXV has failed. Before replacing anything put the system into a deep vacuum for several hours to try to boil off the water in the system, ice can form in the TXV and develop this type of complaint when there is moisture in the system. 

Low and High Side Low: If when the compressor engages the low side drops but the high side does not rise, or maybe the high side drops as well, then there is an obstruction between the compressor and the high side pressure port. All that refrigerant is backing up somewhere, but your gauge can’t see it. 

Low side High, High side Low: If the high side and low side do not change from static pressure when the compressor is engaged, then the compressor is not pumping and has failed. 

Pressures Normal, not cooling: Assuming the blend doors are working normally the system might be insulated from the inside. Something is keeping that cold low side refrigerant from making the evaporator fins cold. Stop-leak can do this, so can an excessive amount of refrigerant oil. 

 

Diagnosing A/C Issues

 

Once you have an idea what’s going on with your pressures, it’s time to start some hands-on diag. This is done with temperaturesensing equipment, either a temp gun, a probe, or with a thermal camera. You can also generically use your hands, they will tell you if something is hot or not, just without the fancy digital readout. If you are using a temp gun, note that measuring extruded aluminum lines can give you false readingscover the line in masking tape and measure the temp of the tape for better accuracy. I prefer to use a thermal probe, that will be the most accurate. A temp gun is useful if you remember to take it with a grain of salt and a bit of skepticism. 

 

Air Conditioning Temperature Readings

 

We know what the pressure and temperature should be normally. If you suspect an obstruction anywhere in the system, it’s time to check line/component temp. Here are some temps you should expect to see on a normal system at about 68°F. 

Discharge line from compressor: This is the hottest part of the systemit should be 15-30 degrees hotter than the liquid line coming from the condenser. At 68° expect anywhere from 130-175°F depending on humidity. 

Along the condenser: You should have a gradual drop in temp from the discharge line to the liquid line, you should not drop more than 50 degrees though, or the condenser may be plugged. Expect 15-30degree drop. 

Liquid line to the expansion valve: This is the “warm” lineyou will see about 15-30 degrees cooler here than the discharge line. At 68°F, expect that you will have 110-140°F. You should have an even temp all the way to the expansion valve. 

Expansion valve: The liquid line going in will be your 110-140° temp, the suction line coming out will be 32-42° almost regardless of the ambient air temp, once the evaporator has a chance to maintain its’ chill. 

 

Common A/C Problem Areas 

 

Check the temperature drop across the condenser50degree drop is a problem. 

Check the temp along all the linesyou should not have any drop at all in the middle of a line, unless that’s where the Fixed Orifice is of course. 

If the temperature of the lines is lower than suggested by the pressure on your gauge, then look for stop-leak or excessive refrigerant oil in the system. 

Make sure to download the temp/pressure chart and graph, hang them up on your box for quick reference. If you run into a weird one that you can’t seem to get your head around, then give us a call here at Identifix. Happy wrenching! 

 

 DOWNLOAD OUR A/C PRESSURE/TEMPERATURE CHART AND GRAPH

 


Find and Fix Faster in Direct-Hit with Super Charged Search

Super Charged Search Direct-Hit

 

When you need to find a location, diagnostic, test procedure, TSB, wiring diagrams, or anything else you may need, you can be sure that one thing you will definitely find is that every OEM likes to have their own unique naming conventions.

Thankfully the power of Super Charged Search in Direct-Hit slices right through that issue and helps you find what you need no matter which term you use and even lets you use common words to locate technical information.

 

An Example of Super Charged Search in Action

 

Let’s say you’re working on a Kia and need info about the coolant pump. Kia, unfortunately,  does not use the word “coolant pump” in their service manuals, but that’s ok cause you have Direct-Hit.

Just type in “coolant pump” in the search window and Super-Charged Search gets to work finding related keywords to get what you need. While you typed just “coolant pump” Direct-Hit also searched for “Water Pump”, “Waterpump”, “Water Pump Location”, “Electric Water Pump”, “Auxiliary Coolant Pump”, “Water Pumps”, “Auxiliary Water Pump” and a number of other similar terms.

 

More Examples? Sure…

 

This time let’s say you are looking at a GM vehicle and they use both “coolant pump” and “water pump” interchangeably, so we’ll show you both.

GM Coolant Naming Search

Another example is a sensor commonly called an O2 Sensor. When we look at VW they call it an HO2S sensor but Super Charged Search still found it when you searched “O2 Sensor” and got you to the right component.

O2 Sensor Search

Using just a few keywords Super Charged Search can make it easier and faster to find what you’re looking for.

 

What About Error Codes?

 

Super Charged Search also works for Error Codes. In fact, you can search up to 8 error codes at a time and all you need to do is put a comma or space between each code

It will also search for common codes associated with codes that you search. In the above example, Direct-Hit also searched for “16804”, “P0420a”, “P0420b”, “Code P0420”, “01056”, “DTC 16804”, “Code 16804” and similar terms.

 

Repair More Vehicles Faster

 

When it comes to finding what you need quickly – specs, codes, test procedures, TSBs, wiring diagrams, or anything else, Super Charged Search is your answer. It does all the hard searching for you so you can concentrate on what you do best, getting that vehicle repaired.

 

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Meet Eric Betts

 

 

Eric Betts’ Credentials

ASE Master Certification, L1 certification, Isuzu and Subaru factory-trained technician. 

 

Eric’s Start with Cars

Eric’s first experience working on cars was when he purchased his 1970 Dodge Charger. This car is what really kickstarted his passion for working on cars and after graduating, he decided to attend Texas State Technical College to earn a certificate in Automotive Technology.

Eric’s Professional Career

After earning his certificate, a shop called Waco Auto Imports then hired him full time to work on Isuzu, Mazda, Subaru, Suzuki, and Daihatsu vehicles. Eric later moved on to work at an Isuzu dealer in the city of Dallas Texas. Eventually, he grew a little tired of that big city lifestyle and moved back home to Tyler, Texas for 6 years to work at the local garage, Crown Auto. At Crown Auto, he continued his work on import vehicles and was their specialist for Isuzu, Subaru, VW, and Kia.

During his time at Crown Auto Eric also received his ASE Master Certification, his L1 certification, and became both an Isuzu and Subaru factory-trained technician. 

 

Joining Identifix

In 1999, Eric moved to Minnesota and began working at White Bear Acura, Isuzu and Subaru out in White Bear Lake, Minnesota. A month later, the family pulled up their Texas roots and everyone moved to Minnesota. Eric’s expertise caught the eye of Identifix and he was recruited to be a Virtual Tech for the Asian car team where he’s been crushing it since 2005.

 

When He’s Not Working

Outside of work, Eric enjoys exercising at the local Farrell’s gym and even instructs classes in the morning. He also loved riding his 4 wheelers and camping with his wife. 

 

Have a particularly tough Asian vehicle sitting in your shop? Eric and Virtual Tech Asian team are ready to help! They’re just a phone call away.