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I just bought a 2002 Civic EX to replace a 2001 Civic EX that was failing. The AC is not working. Here are all my observations/tests so far:
With the engine stopped and the key in the on position, when I press the AC button on the center controls, the green LED lights up but nothing else happens. There is no audible click from the relay and the radiator fans do not engage (like happens on the 2001).
I have swapped the center control units (for other reasons), still nothing on the 2002 and working on the 2001.
I have swapped the relay from the under-the-hood fuse box, still nothing on the 2002 and working on the 2001.
Using a gauge from an AC recharge kit, there is refrigerant in the system.
The AC compressor pulley and clutch spin freely.
There are no trouble codes in the computer.
As we are now out of the summer months, this is not as critical, but any help would be appreciated.
The wire harness on the switch on top of the dryer was connected. I disconnected it and reconnected it a couple of times and no change. I disconnected the wiring harness on my older 2001 test Civic (which this morning went to the salvage yard) and was able to recreate the same symptom there as here on the 2002. When I connected the AC recharge kit gauge to the low pressure side (with the car off) it read about 53 psi.
Is there a way to test the pressure switch? I have a multimeter but am a novice at using it.
Can it be replaced without evacuating the system?
Disconnect the pressure sensor connector. Use your meter to check continuity across it, is there continuity? If you have continuity the sensor is likely okay, but there could be an issue with the rest of the circuit. If the sensor is bad the system has to be evacuated in order to replace it. Also check the number 14 10 amp fuse in the under-dash fuse box.
You can find the service manual at the link below, it has complete troubleshooting steps for A/C issues. Page 21-78 is where the A/C pressure switch circuit troubleshooting begins. https://www.civicforums.com/forums/1...pdated-10.html
Hi again. Summer is back and so am I. A few weeks back I had to switch out the alternator and was able to verify that there is continuity at the pressure sensor (I think, I'm still pretty new with the multimeter). I currently have borrowed a set of manifold pressure gauges. The high and low side pressure are both basically 75psi, all the time: with the engine off, with the engine running and AC off, with engine running and AC on (meaning the light on the button is on).
I'll be working through the service manual stuff to the best of my ability in the near future. Does the info above indicate anything?
That enough pressure to turn the system on. Do both fans come on when the A/C button is pressed? Next would be to verify the compressor clutch. You could check the clutch relay and wiring down to the compressor.
No, to the fans. No, to anything. When I press the button, the only thing that happens is the green LED on the button illuminates. Any guidance you can give on how to check the compressor clutch and the clutch relay?
If the fans don't come on that points to the pressure sensor still. How did you check continuity across it? Set the meter to the Ohms (Ω) setting, if there are multiple settings go for the lowest usually around 200. Touch both probes together to test, the meter should read 0 or close to it. Unplug the pressure sensor (on top of the A/C drier). Put each probe on both terminals of the sensor, be sure not to let the probes touch each other while doing this. If the sensor is good the meter will read something close to 0.
Also check fuse 14 (10 A) in the under-dash fuse box. Since the A/C button indicator works I believe that means the fuse is good but go ahead and check it.
The pressure sensor sends a ground signal to the PCM pin E24. You can also verify continuity from the sensor to that pin.
Fuse 14 in the under-dash fuse box (labeled in my manual as Remote Control Mirrors) is confirmed good. When I took it out the fuse is fine and the A/C button indicator and the fan would not work. When I reinserted the fuse, both resumed working as normal.
I believe I did basically what you described for checking continuity or resistance on the pressure sensor, but I admit, I don't exactly remember. I can't get both my hands down in the space now to control both probes without moving the power steering pump again. I'll run out and get some alligator clip wires for my toolbox. As a different test, could I jump the opening in the connector / wiring harness, with the engine not running, and expect to hear the relay click and the fans to start up? Is that a safe / valid test?
As a different test, could I jump the opening in the connector / wiring harness, with the engine not running, and expect to hear the relay click and the fans to start up? Is that a safe / valid test?
Yes, except you likely won't hear the relays over the fans. Add a jumper between the terminals in the connector then turn the key to the second position (ON), the fans should start up.
Unfortunately, no change. When connecting the two silver contact in the harness with a small piece of small guage wire, nothing at all happened. I'll still do the ohms check on the dryer in the coming days. Any other ideas?
Shoot, I misread the service manual. The pressure sensor runs to the multiplex unit and then it talks to the PCM over a communication line. Do this though, with the A/C button and key on unplug the pressure sensor. Use your meter and check continuity to ground, the blue wire should have it. You can then use a paperclip and a jumper wire to apply ground to the other terminal (blue/white wire). This should engage the fans and compressor.
I didn't get to trying your last idea. I did get to testing the pressure switch and can confirm that there is continuity there. Also, I ran the self-diagnosis function described on 28-8 of the service manual and it reported no errors. I'm off work next week and will be available to try more things.
Do this though, with the A/C button and key on unplug the pressure sensor. Use your meter and check continuity to ground, the blue wire should have it. You can then use a paperclip and a jumper wire to apply ground to the other terminal (blue/white wire). This should engage the fans and compressor.
Give this a try when you get a chance. If you don't have ground on the blue wire with the A/C button on that points to a bad heater control panel or a broken wire between it and the pressure sensor. If you ground the blue/white wire and the A/C does not engage that points to a bad ECU, multiplex unit, or broken wire somewhere in between.
Originally Posted by HR Puffinblunts
Did you try tapping on the compressor clutch at idle to see if it's an air-gap issue between the compressor clutch and (magnetic) solenoid?
I don't think it's a clutch issue because the fans won't even turn on but at this point anything is worth a shot.
Shoot, I misread the service manual. The pressure sensor runs to the multiplex unit and then it talks to the PCM over a communication line. Do this though, with the A/C button and key on unplug the pressure sensor. Use your meter and check continuity to ground, the blue wire should have it. You can then use a paperclip and a jumper wire to apply ground to the other terminal (blue/white wire). This should engage the fans and compressor.
The wires to my pressure sensor are blue and red. When on the lowest Ohm setting, the multimeter read 7.2 when connecting the blue wire to ground. I was not able to get a reading when connecting the red wire to ground (with or without the blue wire connected to ground). It said OL all the time.
Last edited by thebigbarn; Jun 12, 2020 at 07:59 PM.
Next I would go to the multiplex pin F9 and check continuity to ground with the pressure sensor plugged in. Should be the same or very close to the 7.2 you read at the sensor. I honestly don't know where on the multiplex is connector F but here is what it looks like. You'll want pin 9 which should be blue/white according to the schematic but may be red like you saw.
So I'm back to working on the car. Over the past two days I've been testing, following the circuitry and troubleshooting in the manual. I think I've found something. On my car the compressor thermal protector and the pressure sensor are wired in series. I've validated power through most of the places but kept coming back to the pressure sensor. Today I was able to back probe with a paperclip into multiplex pin F9 and got 11.10V when the key is in the ON position and AC is on. There is a blue/white wire coming from that pin but no blue/white wire at my pressure sensor.
So I started tracing the wires back through the harness. Just to the right of the hood latch the harness splits and goes to the pressure sensor and the compressor. This is what I found:
The blue/white wire along with the blue/red go down to the compressor connector:
It would appear that the 11V coming from multiplex F9 is routing first to the thermal protector then back up the red wire which is going to pin 2 of the pressure sensor (where all the schematics indicate the blue/white wire should be).
Furthermore, I tested for continuity through the female connectors of the compressor (bottom section of the picture above) and got OL. There is not continuity, which according to the manual there should be when the temperature is below 241 to 219 degrees (F). It would appear I need to replace this piece. I have not yet been able to jump the blue/white pin to the red pin at the connector to see if everything else works as expected.
These Civics have two different types of A/C compressor connectors, a three wire connector and a single wire connector. The schematics appear to be for the single wire setup where the thermal protector is built onto the compressor and directly disengages the clutch when it's too hot. The three wire setup could be setup where the thermal protector is in series with the pressure sensor and shut the system down that way. It would be nice if this was noted in the service manual.
For the three wire setup the blue/red wire should be for the clutch coil, the other two for the thermal protector. So if you had OL on the correct two wires on the compressor side of the connector then either the thermal protection is bad or the wiring down to it is bad.
I was able to jump the blue/white pin to the red pin in the field coil connector and everything appears to be "working" - meaning, with the key in the ON position, the blower on, and pressing the AC button, I hear the click in the relay and the condenser fan turns on!!
The Compressor Thermal Protector Replacement diagram on page 21-51 does not show the supply line pipes but looking down into the engine compartment, it looks like this part could be replaced without having to evacuate the system and remove the lines (after removing the power steering pump and alternator). Do you have any tips about replacing it?
I have not had the pleasure of replacing one. The service manual I have shows the single wire connector type so it will be slightly different than what you see. You won't have to evacuate the system as long as you can get down to the bolt on top.
When I look up a part number it is also showing the single wire type. You may end up having to swap to this setup. You would then connect the blue/white and red wires together on the body side and swap the connector to accommodate.
Today, while I wait for the new thermal protector to arrive, I bypassed the thermal protector by splicing together the two wires between the connector and the compressor so that I could check the compressor/clutch. It's a good thing I did because all it did was make a grinding noise. I can spin the compressor clutch by hand and it feels like there is a "normal" amount of resistance. I was able to get the clutch center nut off and the clutch plate was very rusty. I have cleaned it and the pulley pretty well and am still working on it. The last time I tested, it began turning a little. There is a bit of a groove in the pulley that appears to line up with the pins. Is that supposed to be there or does that indicate significant wear and it should be replaced?
After quite a bit of work with sand paper and wire wheel I was able to get it back to working order. The compressor clutch engages and seems to be working well. I got manifold gauges from Autozone Loan-A-Tool and saw the pressures changes when the compressor engaged. I got some additional refrigerant and added it in and got it to blowing a cool 42 degrees. I'm looking forward to getting the faulty thermal protector replaced and getting it back on the road.
Yesterday I was able to get the part replaced. It required removing the power steering pump and alternator to get to it. Once exposed, the 8mm screw came out easily. The old thermal protector, not so much, of course. It required drilling out the majority of the old switch components and scraping the metal housing clean before I could get the new one in. I got the part from HondaPartsNow.com and it was the correct match for my existing three wire harness.
Everything worked very nicely while driving today. Thanks again to all who posted in the thread. I learned a lot and am back on the road in comfort.
AC system won't engage 
