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A/C Diagnostics - A Crash Course in Cooling Concepts
Alright guys, I promise I am writing this out of the kindness of my heart and not because I'm already tired of the annual "Why isn't my a/c cold" threads that seem to pop up at the same time as my seasonal allergies. I am hoping that with both a combination of common sense and a dash of using the darn service manual, we can all be a little bit happier. With that said,
How Does Air Conditioning Work?
The air conditioning system in your Civic uses a couple different parts, pieces, and phase changes to deliver magical, ice cold air to the comfort of our own vehicles. I'm going to start with a really scary looking parts diagram, just so everyone is on the same page.
Now, for those of you who are newer to cars, or to air conditioning systems, that might be a whole lot of gibberish. If you aren't acquainted with these pieces, I'll get into their function here. If you think you've got this part down, feel free to skip ahead. You won't hurt my feelings.
Refrigerant: I know, this one isn't on the diagram. Refrigerant, or R134 as you'll see fairly frequently, is a really neat chemical. A refrigerant is any chemical that can easily boil from a liquid into a gas, and then be condensed from a gas back to a liquid. Water is, in fact, a refrigerant - we can easily boil it and condense it, almost infinitely. But in regards to cars, we use R134a, which is a special breed of refrigerant. It's used in a/c systems because it is very, very good at getting cold quickly and can be used in a sealed system indefinitely to continue changing from a gas to a liquid and back again. When someone suggests you check your refrigerant, this is what they're referring to.
Oil: Again, not on the diagram. But important. A/C oil, or PAG oil, or any number of other names, is a special kind of oil used throughout your a/c system to ensure everything travels smoothly, doesn't dry out, and your a/c compressor's spinning pieces don't eat themselves up. You can often buy refrigerant with oil already added to the can at your local parts store.
High Pressure Service Valve: We're going to start here, because we have to start somewhere. The high pressure service valve is one you'll rarely touch, but is an excellent starting point for the "high pressure" side of your air conditioning system. The high pressure side of your system is, in simple terms, everywhere your refrigerant is a liquid instead of a gas.
A/C Compressor: This is where the high pressure system "begins", I reckon. The compressor does what it says on the tin - it compresses the refrigerant, which makes it more readily cooled. When you hit the a/c button in your car, you engage the a/c compressor by means of a clutch. Hit button, clutch engages, compressor comes to life.
A/C Condenser: Once the super compressed refrigerant has left the compressor, it's run via high pressure lines to the condenser. The condenser functions just like your radiator - it runs the refrigerant through very tiny tubes in between fins that pull air from outside through the fins and across the tubes. That process aggressively cools the refrigerant, like your radiator cools your coolant. This allows the compressed gas refrigerant to condense, becoming a liquid.
A/C Fan: This aids in pulling air through the condenser. If your fan isn't kicking on, you aren't going to be pulling the air through, and the refrigerant will not get cooled.
Receiver/Drier: This is a nifty little box full of stuff kinda like those silica packages that come in food, labeled "Do Not Eat". In short, it sucks all of the moisture out of the refrigerant. Wet refrigerant is unhappy refrigerant, and we can't have that. Once your refrigerant has been sufficiently cooled, it ends up here so it can be about 20% cooler.
Expansion Valve: This is where the magic really happens. See, in order for the refrigerant to stay a liquid, it has to be kept under very high pressure. The expansion valve is where it can kick back, relax, and expand slightly. Not enough to turn back into a gas, but enough for it to mellow out a bit. While it isn't labeled on this diagram, it's back by the evaporator.
Evaporator: Another tiny radiator! Surprise, you get an extra one! At this point, your refrigerant should be coming in at about 32F/0C. This radiator isn't supposed to cool down the refrigerant so much as absorb heat - I know that sounds like the same thing, but I promise it isn't. This part is why we've got a receiver/drier though - having water in there, you'd see it freeze and cause all sorts of problems. As the refrigerant comes into the evaporator, it's exposed to roughly cabin temperature - it's hanging out kinda back behind your glove box, after all - and that warmth from the cabin is enough to boil the refrigerant and turn it back into a gas.
Blower Motor: Again, not shown above, but this little fan guy is what pulls air through your evaporator and gives you that sweet, sweet cold air you so desperately crave.
Low Pressure Service Valve: This is your check point between the evaporator and the a/c compressor. From here, the refrigerant goes back to the a/c compressor and everything starts all over again. This is the port you'll use to add refrigerant you bought at a parts store, and the port you'll interact with the most in general.
Okay Sure, How Do I Fix It?
Yeah, I know. This is the part you care about. I have broken down the Factory Service Manual diagnostic tree here, so pretty please try and follow it? It's from the guys who made the cars, I just work here. I've added a few obvious branches as well, just to cover our bases.
Before you start in on any of this, check fuses 41 (80A), 39 (50A), 13 (7.5A), and 35 (20A).
Does your a/c system come on at all?
Yes? Skip ahead.
No? Check out my comment below.
Is your a/c fan running when you have a/c on?
Yes? Skip ahead.
No? Check out my comment below.
Does your compressor clunk on/visibly move when you hit the a/c button? (Get a friend to help)
Yes? Skip ahead.
No? See my comment below.
Is there refrigerant in the system?
Yes? At the correct pressure? Cool, keep going.
No? Top that off. Instructions for testing pressure are in my comment below.
It starts out cold, but doesn't stay that way.
Try replacing your expansion valve and receiver/drier. The receiver/drier should really be replaced any time you open up the a/c system on these cars, because moisture from the air is enough to damage it quite a bit, and it's something you can only do when you've vacuumed the system out anyways.
You didn't list my issue/I did everything right and it's still broken.
Re: A/C Diagnostics - A Crash Course in Cooling Concepts
Okay, I told you to check out my comment below. I know. I'm writing it right now. Hold on.
Your A/C System Isn't Coming On At All
1. Did you check those fuses? Did you really? Do it again.
2. Disconnect the 2p pressure switch connector on the LH/driver's side of the condenser. It should have a blue/red striped wire on one side.
A. Turn the car on - not running, just on.
B. Put your red multimeter probe on the terminal with the stripey wire, and your black multimeter cable on the battery ground (or any other ground).
C. Is there battery voltage? If so, skip down to Step #5. If no, keep going in order.
3. Disconnect the condenser fan relay connector. It's gonna be a really goofy relay, bolted somewhere off to the side. Kinda a nondescript box, about the size of a... I don't know, you'll know it when you see it.
A. The car should still be on, fyi.
B. The connector will have four wires: one that's black/yellow striped, one that's blue/red striped, one that's blue/black striped, and one that's plain white.
C. You want your red multimeter probe on the pin that's connected to the black/yellow stripey wire, and your black multimeter probe on battery ground (or another ground). Is there battery voltage? If no, you've got a broken wire between that pin and the under-dash fuse box. Good luck. If there is power, keep reading.
4. Time to test that condenser fan relay! Go shut your car off.
A. Alright, so if we're looking at the relay pins/terminals dead on, with the slot for the connector tab at the top, we're doing this right. Top left is #1, top right is #2, bottom left is #3, and bottom right is #4.
B. Break out your trusty dusty multimeter and test for continuity between terminals #1 and #3. If there's continuity, keep going. If not, replace it. **Author's note - the service manual only says to "check for continuity" - I am assuming that means it should be there.
C. If you put 12v of power to #2 and #4, there should still be continuity between #1 and #3. If not, replace it! If everything tested good, you've got a broken blue/red stripey wire between the relay and the a/c pressure switch. Get hunting!
5. Start here if you had battery voltage back in Step #2! Go turn your car off, we've got more electrical pixies to hunt down.
A. Test for continuity between the two terminals on the switch. If you have continuity, plug the switch back in and skip down to Step #6. If not, keep reading here.
B. Check and make sure you have refrigerant pressure. Slap those gauges on, make sure they give you a number that's about the same on the high and low pressure side. If there's no pressure, or low pressure, fill her up!
C. If there is pressure, replace your pressure switch. You should be good to go!
6. Go unplug the 2P connector from the thermo switch. It's back in the greater evaporator area, so you're gonna have to tear your dash apart quite a bit. You're looking for a connector that has a yellow/white striped wire and a blue/red striped wire.
A. Turn your car on, and put your red multimeter wire on the connector pin with the yellow/white wire, then ground your black multimeter probe on any convenient ground. If you have voltage, keep reading. If you don't, you have a broken wire between that connector and the a/c pressure switch. Go fix it.
7. If you did have battery voltage, turn your car off. We're going to test your thermo switch (or, if the following sounds awful, you can just replace it. Your call).
A. Yeet that switch into a pan with some ice water, and test for continuity between the two terminals. There shouldn't be continuity around ~33-35F, and there should be starting around 36-41F. If it's out of spec, replace it. **Author's note - these values are referred to as the "cut off" and "cut in" values. I am assuming that means when there is and is not continuity, given the context provided, but I can make no guarantees.
B. If your switch is good/you replaced it and you still have issues, keep reading. Otherwise, congratulations!
8. Go ahead and dismantle your dash a little bit more, so you can remove your HVAC control panel. Unplug it, we only care about the connector/harness side right now.
A. Test for continuity between pin 10 on that connector (with the blue/red stripey wire coming out of the back) and that blue/red striped wire at the a/c thermo switch on the evaporator. If you have continuity, keep reading. If you don't, the wire is broken somewhere between that connector and that switch. Good luck.
B. Now, unplug the little 6P connector on the backside of the HVAC controller if you haven't already. That's your heater fan switch connector. In the top right corner, there's a pin. The wire coming out the backside should be green. On that 14P connector, there should also be a pin with a green wire coming out of the backside. Test for continuity. Have it? Keep reading. Don't? Fix the broken wire between the two connectors.
C. Alright, now in the top left corner of that 6P connector should be a pin connected to a black wire. Test for continuity between that and body ground. If you don't have continuity, inspect the wire to see if it's broken anywhere. If it looks good, check grounds 201 and 401. (No, I don't know which grounds those are. Sorry.) If you do have continuity, replace your heater control panel.
Re: A/C Diagnostics - A Crash Course in Cooling Concepts
Your A/C Condenser Fan Doesn't Turn On
Alright, so the entire fan in front of your condenser doesn't work. It's probably just as old and tired as I am. Let's jump into fixing it.
1. Did you check those fuses I mentioned? Do me a favor and check them again, just to play it safe.
2. Locate and unplug the A/C Condenser Fan Relay. It's gonna be bolted up towards the front, and it'll have four wires: blue/yellow striped, blue/red striped, blue/black striped, and white.
A. Now it's time to build a jumper wire. Historically, I've used a paperclip. Then I put some really gnarly burns in my hand. Now I use insulated wire, with the ends stripped and twisted together. If you wanna play the danger game, I can't stop you, but don't blame me when it hurts.
B. Take your jumper wire and jam it into the connector, into the top right and bottom right slots on the connector (aka the blue/black stripey wire and the white one).
C. If the fan runs, continue to Step #3. If it doesn't, skip down to Step #5.
3. Turn your ignition switch on and pull out that jumper cable, then grab your multimeter.
A. Put your red multimeter lead into the slot on the connector that has a black/yellow stripey wire coming out of the back, and ground out your black multimeter lead wherever you'd like.
B. If you have battery voltage, hop along to Step #4. If you don't, you've got a break in the black/yellow wire somewhere between that connector and the under-dash fuse box. Good luck and godspeed, my friend.
4. Turn your car back off, and unplug the A/C Pressure Switch. Little 2P guy up front by the LH/driver's side of the condenser. Has a blue/red stripey wire.
A. You should still have that relay unplugged. You know the slot with the blue/red stripey wire coming out the back? Put one end of your multimeter in there, and the other end into the side of the A/C Pressure Switch connector with the same blue/red stripey wire in the back. Test for continuity.
B. If you have continuity, replace your condenser fan relay and enjoy a working fan. If you don't, you have a break in that blue/red stripey wire. Time to get searching!
5. Start here if you jumped your relay connector and it didn't do anything.
A. Stick the red multimeter probe in the relay connector, where the white wire is. Ground out your black probe wherever you want that's actually a ground. Test for voltage.
B. Have battery voltage? Go to Step #6. No voltage? You have a break in that white wire between the relay connector and the under-dash fuse box. Go fix that.
6. On the condenser fan proper should be a 2P connector, with a blue/black striped wire and a plain black one. Unplug that.
A. Stick one multimeter probe in the connector slot with the blue/black wire coming off the back, and stick your other multimeter probe in the relay connector slot with that same blue/black wire.
B. Test for continuity. If there isn't any, that wire is broken - go ahead and repair it. If you do have continuity, keep going.
7. Supply 12v of power to the blue/black wire terminal on the fan, and ground to the black wire terminal on the fan.
A. Does it run? If no, go replace your fan. You did it!
B. If it does run, the ground is bad. If the black wire looks okay from the connector to its end, check for poor ground at G751.
Re: A/C Diagnostics - A Crash Course in Cooling Concepts
A/C Compressor Clutch Not Engaging, or A/C Compressor Diagnosis 101
I'm sorry for the delays in getting this pieced together; I'm very overworked and even more underpaid, so my hobbies often have to take the backseat. But we're back and sleepier than ever, so let's see if I can make this coherent!
You might not be sure of how to know if your compressor is or isn't engaging - I don't blame you. It's kinda a pain to identify if you don't have somebody to help, and even then it can be hard. The easiest way to spot it is to get a friend and have them sit in the car. Get it running, and have them hit the A/C button. Watch the front pulley bit of the compressor - if it moves, you're probably okay. But that isn't hard and fast, so if you have your doubts, just follow these steps anyways.
1. Yada yada go check those fuses.
2. Disconnect the A/C thermostat 2P connector. I couldn't tell you what wires it has, but it's a little connector hanging out on the evaporator that plugs into a small box on the side.
A. Stick a jumper wire in the harness side. Author's note: I believe it's the harness side, although that isn't specified. Please read my above repair guidance for info on jumper wire safety.
B. Start your engine. If the A/C compressor now works, replace your A/C thermostat. If it doesn't, keep reading.
3. Turn your ignition off, plug the thermostat back in, and unplug the compressor clutch relay up front. Four pin relay, bolted up in the front somewhere, I've talked about it in previous comments.
A. Measure voltage between the upper right harness-side hole (the one with the white wire coming out of the back) by sticking your red multimeter probe in there and your black multimeter probe on a ground.
B. If there isn't battery voltage, that wire is broken somewhere between that connector and the under-hood relay. Go fix it.
C. If there is battery voltage, keep reading.
4. Go turn your car on real quick. Measure voltage by moving that red multimeter probe over to the left one, to where the black and yellow striped wire is poking out the back.
A. If there's not battery voltage, that wire is broken between there and the under-dash fuse box. Get fixing.
B. If there is battery voltage, keep reading.
5. Time to test that relay! Shut your car off again.
A. Please see above for details on how to do so. If it's bad, replace it. If it's good, keep reading.
6. Disconnect the little 1P connector at the A/C clutch. He's a little guy.
A. Now you're going to measure for continuity between the pin on the harness side of that connection and the harness side of the A/C compressor relay - specifically, the pin on the harness side of the connector that has a red wire coming out of it.
B. If there isn't continuity, the wire is broke somewhere between those two points. Fix it.
C. If there is continuity, keep reading.
7. Guys I'm too tired I'll finish this later. I have a job interview in the morning, wish me luck!
Re: A/C Diagnostics - A Crash Course in Cooling Concepts
Thank you for doing this - subscribed!
Looking forward to reading.
I am on the midst of replacing all my o-rings in my EG hatch, along with condensor, receiver/dryer. I already upgraded my evaporator to the newer version w/ cabin filter.
Re: A/C Diagnostics - A Crash Course in Cooling Concepts
Originally Posted by Shark Party
Now I understand why I had to replace all those parts. AC is working well now and the car drives now.
That's the goal! I know A/C stuff gets expensive and tedious very quickly, and I figure if people understand what they're doing and why, it can make everyone's life a little easier.
05-06-2021, 04:45 PM
A/C Diagnostics - A Crash Course in Cooling Concepts
