The AC on my 2002 Honda Civic EX coupe (80k miles, auto)stopped working. When I jump the Compressor relay, the compressor kicks on. Otherwise, I can not get the compressor to come on. What parts are between the AC button and the compressor relay? Is there some other fuse or relay that has gone bad? Thanks.

 

Does the condenser fan start when you try to run the A/C (everything connected normally)?

Especially if the fan works, the most likely reason for this is all the refrigerant has leaked out and the compressor is shut down by the pressure switch to protect it. The first thing to do with such a case is to put pressure gauges on and check the refrigerant pressure. If you don't have gauges, locate the pressure switch on the receiver-drier tank near the left fender. Unplug it and check the switch for continuity with an ohmmeter. If the switch is open you have probably experienced a severe leak somewhere in the system.

Do not try using "stop leak"! That stuff never works, and will totally ruin your A/C system.

 

Thanks for the reply.
The pressure at the low port reads around 100 PSI. I do not have a gauge for the high port. I read in another thread that the pressure will tend to level out between the 2 ports when the system is not active, that would explain why the low port pressure is so high? Not sure if the condenser fan is starting, I will have to check tomorrow.

As far as the pressure switch goes, I did not check it for continuity, but I did use another suggestion from the forum and I jumped it with a wire and it did not cause the compressor to start. I was looking at the wiring schematic for the ac system and from what I can tell the pressure switch is in a different circuit than compressor relay (however i am not experienced at reading schematics at all, so this is only a guess. I am including scans of the diagrams in this post if someone with expertise can take a look). Anyways, that seems to suggest that the pressure switch is not the problem if the compressor kicks on fine when I jump the relay. Or it could be I have no idea what I'm talking about....


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The diagram is quite useful. It is different from the older models. Here is basically how it appears to work:

The heater control panel uses the blue wire to tell the rest of the system that it wants the compressor to run. Probably it pulls the blue wire to ground but it might also pull it positive instead. Anyway, the voltage on the blue wire should change when you press the A/C button.

This signal passes thru the pressure switch and the thermal protector. Your pressure is OK at 100 psi, the compressor should run. If those two sensors are closed indicating that it is safe for the compressor to run, the signal from the control panel eventually reaches the multiplex control unit. That unit converts the signal to a digital code and transmits it to the ECU via the yellow wire. The ECU then decides if it is ready to run the compressor. Finally the ECU drives the fan relays (both are connected in parallel, so both fans should always be either on or off in unison) and the compressor relay to start the A/C cooling.

So jumping the relay doesn't prove much because it is the last thing in the chain. If the engine idle speed increases when you press the A/C button, the ECU is wanting to engage the compressor and maybe just the compressor relay is bad. If not, I would try probing the voltage at the blue/white wire at the multiplex control unit, if it is responding to the A/C button it is going to be something with that unit or the ECU, if not it is the control panel or one of the sensors.

 

Ok thanks for the information, it makes more sense now. By your explanation, one of the first components in the system is the pressure switch. With the AC turned on, I checked both contacts on the pressure switch for voltage and got nothing. I looked for any loose or corroded wires, didnt see any. I guess I should start from the AC switch and work forward to the switch to see where the signal gets lost. I checked the fuses under the dash and they all look good. There looks like there are relays under there as well but they are not labeled or easily accessed. Anyone know of something before the pressure switch that I should check?

I also have a question about the electircal schematics. On the first diagram, why are there 2 more wires labeled Compressor Ctrls (BRN and LT GRN)? It looks like one of them goes to an AC Relay in the RECIRC-AC-DEFROGGER Swith Assembly, should I and can I check this relay?

 

It appears that the heater control panel contains a small computer which coordinates the control inside the car. It's going to require these conditions:

The interior fan is on
The driver has pressed the A/C button on the 3 button switch
(When these first two are true, the heater control panel responds by lighting the LED on the button.)
The evaporator temperature sensor reading is OK (evaporator not too cold).

Thus the temperature sensor and three-button switch are inputs into the main control panel. The output is the blue wire that goes to the other page. This will eventually lead to the compressor starting. Note that normally as you drive the control panel might cut the compressor on and off according to the temperature sensor, after the air from the vents is very cold.

You should test the blue wire at the pressure switch with the A/C off as well. It's quite possible that zero volts on the wire is compressor on and more than zero volts is compressor off. If you have no activity on the blue wire at all it could be the 3 button switch or the evaporator sensor or the heater control panel itself. Without knowing specific voltages, resistances, etc. to look for it could be hard to troubleshoot exactly. You may need to consult a factory manual or alldata, etc. for more specific information.

 

Thanks, I will try to testthis week. I appreciate all of your help with this.

 

I have the same problem withmy 03and just had a quick question. I have the manual and it gives you a bunch of things to test and one of them is to see if thatblue wire you mentioned has power to it. If it does, use a jumper wire to connect it to ground. If the compressor starts up, replace the heater control panel. My question is, is there any way of knowing for sure that it'sthe knobpanel and not the button panel? I can buy a used one for about $100, but if i return it, I can only get store credit, which kind of sucks. Also, can't I just connect a switch to that blue wire and connect that to ground, or does the control panel do something?

 

More likely it's going to be the control panel with its computer and all because the button panel is just a button. You should be able to unplug the button panel and jump the two wires that go to the A/C button together and see if it starts then, if it does then the button is bad.

If you were to ground the blue wire with a switch your evaporator may freeze sometimes because the temperature sensor (which feeds thru the control panel) will be bypassed. This doesn't hurt anything but the system will stop blowing cold air until you thaw it out manually (by lifting the ground so the compressor stops). If it were the middle of summer and you didn't have cash for a new panel, rigging something like that could keep you cool.

 

Hi,
I have a similar problem with my 2002 honda civic. The electrical shop diagnosed it and said that the compressor is always ON no matter what. The tech also said that the Heater Control panel has constant ground output and needs to be replaced.

I am confused as to replace the heater control panel ( the one with the *****) or the A/C switch(on the horizontal panel).

Thanks