kev2182

Hi all,
I'm looking for advice on what might be wrong with my 2004 civic. The A/C won't get cold. The pressure in the system is fine (checked on both high and low sides). The blower seems to works fine - just no cold air comes out. The switch on the dash lights up when the AC button is pushed (indicating to me the switch is getting power). All fuses are fine and when I switched relays in the under-the hood fuse box with others of the same size in the box nothing changed (so I assume those are all fine too).

When I ground the A/C compressor I am able to activate it and I can see it kicks on. It seems like the circuit is activated by grounding the system? If this is the case is there a relay in the system that grounds the A/C compressor to activate it?

Any suggestions on what might be broken or other things I might be missing?

Thanks!
-Kevin

It Wasn't Me

I suggest you buy a Helm's manual. The A/C has a number of components that may prevent the system from working properly.

Pressure switch, thermal protector, loose wire / bad ground, etc. would be places to start looking since you've checked fuses and relays already.


Edit: Here's a link for the manual. http://www.helminc.com/helm/product2...C01&itemtype=N

eviee1973

Try another multiplex box, mine takes fits once in a while with intermittent erratic operation. Problem disapeared for nine months, then came back. Everything seemed to check out with shop manual specs, and this is the master control for the ac system.

kev2182

I've been continuing to try to diagnose this problem with the A/C. I thought it might be a problem with the a/c pressure sensor. I pulled the harness on the sensor and tried to measure 12v across the wires - nothing.

This makes me think that the problem is before the pressure sensor. I'm not sure where though. Does anyone know what is in the circuit before the pressure sensor that could be causing this problem? Could this be a problem with the thermal protector on the compressor?

kev2182

Quoting:

"Try another multiplex box, mine takes fits once in a while with intermittent erratic operation. Problem disapeared for nine months, then came back. Everything seemed to check out with shop manual specs, and this is the master control for the ac system."

I thought this might be causing the issue - but from what I've read online when this goes I would expect to see other problems (e.g. wipers, lights, etc). I only see A/C problems and when I ground the relay I get the compressor to work which makes me think the problem is in the circuit somewhere - a bad ground perhaps... any more advice you can provide will certainly be appreciated!

kev2182

Finally figured out what the problem is - a bad thermal protector. I used this protocol I found elsewhere online to figure it out -

On this system the A/C compressor request circuit is somewhat complicated. The A/C request signal is sent to the PCM via CAN communication from the instrument cluster. The instrument cluster receives an A/C request signal from the under dash fuse relay box multiplex control unit. The under dash fuse relay panel multiplex control unit receives its request signal from the A/C control panel but that signal has to pass through the thermal protector on the compressor. Hint: the A/C control panel will not give a compressor request signal when the blower motor is inoperative.

Unplug the three pin connector on the A/C compressor and check continuity across the thermal protector wires. If the circuit shows to be open and there is no continuity, the thermal protector is bad. The wires for the thermal protector are Blue/White and Red. Jump those wires together to bypass the thermal protector and then verify the A/C compressor comes on. The thermal protector is available separately. If there is proper signals, powers, grounds to the compressor and the compressor still does not activate, the compressor clutch is faulty.

Test the voltage on the BLU/WHT wire at the thermal protector to determine if it has a 12 volt reference, if not, check for an open wire between the under dash fuse box and the A/C compressor. If there is a reference voltage, ground the wire with the engine running and the blower fan turned on and see if the compressor turns on. If the compressor turns on this would indicate that the A/C request circuit to the Powertrain Control Module (PCM) is good and the problem would be with the A/C request signal coming the from A/C control panel.

The A/C control panel should apply a ground to the Red/Black wire at the thermal protector, when the A/C switch is turned on. If the control panel is not grounding the wire at the thermal protector, check for an open wire between the thermal protector and the A/C control panel. there may be a bad input to the control panel if the Red/Black wire tests good.

Raju

hi there i have the similar problem but my car AC stops working during hot time only. morning and evening its all fine works good i have cheked pressure switch condenser fan and relay so fan, freon, heater controle panel switch i did not get any issue with those things is there any thing that i can check please help... thank you

imadigitalgod

mine is doing the exact same thing. i measured voltage to the thermal switch the whole time that the compressor didnt kick on. What I am doing is getting a new thermal protector switch, i will let you know if that fixes the problem for me, maybe its the same thing for you.

Albertx22

Hey guys, sorry to try to start up a old thread. Just really puzzled with my AC right now. I have a 03 Civic EX, compressor only seems to run when cold out, so I jumped the thermal protection, nothing, I've check voltage at the relay, replaced relay, replaced pressure switch, replace receiver, & charge. I start the car in the morning, compressor started, made very nice/cold air for about 15 minutes, then shuts off & won't come back on. PLEASE HELP ME.

John Duffield

.
^^ Mate im in the same boat as you.
I feel your pain. I have given up and gone to a mechanic who is quoting $950 for the compressor not including labour.
I know its not the compressor because discharge and suction pressures were fine.

NDNV

FWIW and I am no A/C expert, but this was my symptom and easy solution:

The A/C would fade out after a few minutes of driving. The A/C light would stay on as if the A/C was working properly but cold air would fade out to warm (this was in the summer). The solution was to remove the clutch and take out one of the small shims so that the coil would stay engaged. Over time the spacing must have become too far that the coil could not keep the clutch engaged, hence no A/C. $40 labour and all is fixed. Just in case this can be of help to anyone. $40 is a lot cheaper than the dealer's recommendation of replacing coil and clutch for $$$.