I have a 2002 Civic ex coupe and have intermittent air conditioning.

I have a factory service manual (computer version) that I have been trying to follow to diagnose the problem.

My green light comes on but neither the compressor or either of the fans come on when it is not working. When it works all three come on and the air is cold.

There are no codes (blinking lights) when I run the cars self evaluation by pressing the recirc and ac button etc.

The FSM tells me that if no fans come on and the compressor doesn't kick in to troubleshoot the a/c pressure switch circuit.

My FSM states that it is for the 4-door and 5-door KE model but I have a 2-door coupe with trunk, I don't think they are different for the A/C troubleshooting (tell me if this is wrong).

I tested the A/C pressure switch 2P connector by turning on the ignition switch and placed a multimeter between the No. 2 connector (blue/Wht) and the negative battery terminal. It asks if I get batter voltage but the wiring picture shows a picture with the voltmeter and the symbol for continuity. This is where I'm a bit confused. I get 1.8 volts. I do not get the full battery voltage of 12.4 volts. Is it supposed to be the same voltage as the battery here?

I also went to the section that is if you answer no to the battery voltage and it says to check under-dash fuse/relay box connector F (12P) and body ground with the connector still connected. Here I get the full 12.4 volts of the battery. The wire I'm touching in the fuse/relay box looks to be the same blue/wht wire that connects to the pressure switch. Do the voltages need to be the same?

I then, assuming that the wire is bad, took a jumper wire to give the blue/wht wire at the pressure switch connector the full 12.4 volts by jumping it to the positive battery cable. I, at the same time, jumped the pressure switch to the other connector to see if the fans and compressor would kick in with the full 12.4 volts power. It did not. I wanted to try the full power before routing a new wire from the fuse box inside the car all the way to the pressure switch connector. I'm glad I did.

Now I'm confused though.

The other way I could have gone, according to the FSM, was to check the pressure switch for continuity after turning the ignition switch off. I checked and it had no continuity between the two prongs.

It then says to check for proper AC system pressure. I had earlier checked the pressure when the compressor was running to be around 35 I think on the low side. The refrigerant bottle said that it was in the good range.

It says if the pressure is good then replace the pressure switch.

Before I go through with that process, does anyone think that it the problem?

Could it be the thermal protector? That thing looks rusty.

I'm lost at this point since I'm not sure if the 1.8 volts is enough voltage to consider batter voltage.

Suggestions?

 

The different body versions all have the same A/C system.

Pressure switch should have continuity with the system charged (which obviously it is, since you sometimes get cold air). I suspect the switch may be bad. Refrigerant must be removed to replace the switch-- of course you already know that having the service manual.

The controls work on negative logic. A voltage near battery voltage in the pressure switch circuit corresponds to system off. The control panel pulls it near ground to signal the MCU / ECU to start the compressor and fans. Since the pressure switch is normally closed, you should measure the same voltage on both pins with everything plugged in. Having different voltages on the two pins confirms the switch is not closed.

If you're going to jump something (NOT recommended), jump it to ground, or jump across the switch, but only as a brief test. Realize that with the switch bypassed, there is no protection against over pressure, which can cause damage and/or personal injury.

 

When I jumper the connector (that attaches to the pressure switch) to act like the pressure switch has continuity the system should kick on. It doesn't.

Maybe the pressure switch is not working in addition to another problem with the wiring to the pressure switch?

Changing the pressure switch to one that has continuity across the leads would be the same as jumping the pressure switch connector right? It should still run. I can't figure out why it doesn't.

 

I didn't check the voltage of each pin with everything plugged in.

Is that something that I need to check? Would I do that with the ac on or off; with the key just on or running?

So would you say that with the ac turned on that the voltage at the pressure switch would be less than the battery voltage of 12.4? So that it might be normal to be at 1.8 volts with the ac trying to turn on?

I jumped the connector just for a short test like you said. I wouldn't leave it on that way. But the test should have the system run though right (fans on compressor on)?

 

I still have no Ac. I just don't know what to do next.

I'm thinking that since the Ac does not run with the pressure switch jumped that there is another problem, possibly the thermal regulator ( not sure of the name, the one that stops the system from working when the temp is too high, it's on top of the compressor and looks pretty crusty).

If the pressure switched is jumped, could the thermal regulator stop the system from working?

 

Do you have a 1 wire plug to the compressor or 3 wire? The 3 wire setup with small wires on the thermal switch has the thermal switch in series with the pressure switch. It should be closed in normal operation.

The 1 wire setup has the thermal switch in series with the compressor clutch. If it were open the condenser fans would start when you press the button but the compressor would not. Also you can unplug compressor and test for continuity. Resistance from the compressor wire to ground (through the switch and coil) should be 3 or 4 ohms.

 

Ok I replaced the thermal regulator. (I tested wrong and the pressure switch has continuity)

New problem.

The Ac works when the Ac is turned off but not when it's on.

It even runs both fans and compressor when the blower fan is off.

I unhooked the battery, hit the brakes several times, and waited 2 minutes before hooking the battery back up.

Same issue.

I disconnected the pressure switches 2 prong connector and that stops the Ac from running.

I also disconnected the connnector for the thermal regulator (the one on top of the compressor that I just replaced) and the Ac stops then too.

I checked the number 1 under the hood fuse and it was ok.

I'm guessing that since disconnecting the pressure switch and thermal regulator stopped it from running that I am protected from doing further damage to the Ac system.

Any ideas?

 

thanks for all the information guys