Jon Petersen

95 Civic EX, EJ1. Recently replaced my condenser and charged the AC. It blows cold intermittently, sometimes working on startup, sometimes working 5 minutes after, sometimes not at all for the entire drive. The intermittence makes me pretty certain it's an electric problem. Anyone have experience with AC electrical systems? Thanks friends, any help is appreciated.

mk378

First thing to do is when it is not cooling, pull over leaving the engine and the A/C button on. Look under the hood to see if the condenser fan is running and if the compressor clutch plate (not just the pulley) is turning.

Intermittent engagement of the compressor with the fan running all the time is usually because the clutch gap is too wide or the compressor relay is bad. The compressor and the fan run on the same fuse. The

Jon Petersen

The last part of your text got cut off. So, when I've pulled over and checked it, what goes on is that the condenser fan and the compressor clutch both disengage at the same time. That makes me think it's the condenser thermostat, but I'm not sure.

mk378

Evaporator thermostat you mean. There is no condenser thermostat.

Since the condenser fan also stops, it probably is a problem with the controls inside the car.

The controls consist of the fan switch, A/C button, and evaporator thermostat all wired in series. When the driver wants A/C and the evaporator is not too cold (over 35F), the wire to the pressure switch is grounded which should start the condenser fan and compressor.

Jon Petersen

Yes, I meant evaporator thermostat. Would a problem with the controls have the effect of turning on or off the AC after the car has been running for a while? Also, when I've tried pressing the button on and off, that doesn't work to switch it on, but it could be something other than the button.

mk378

You'll need to check through the circuit with a voltmeter. If you remove the glove box you can reach the wires on the evaporator thermostat.

Jon Petersen

I'm not very experienced with electrical. It's been suggested to me that I jump the two non-ground prongs with a paper clip. For checking the circuit, do I just measure the voltage between the two non-grounds on the male connector?

mk378

One of the wires is a live from one of the fuses under the dash, don't mess with that. It powers the circuit inside the thermostat box. The two other ones are the control circuit. It goes to ground to turn the compressor on. This is called negative logic. Measuring from a wire to ground, battery voltage would mean the system is OFF and near zero volts would mean that it is ON.

If you jump those two together or ground the one that goes to the pressure switch, the compressor should start.

Jon Petersen

So is it a diagnostic to jump the wires? What would the permanent solution be if I found that the thermostat was the culprit?

mk378

The remedy for bad thermostat would be to replace thermostat. Driving with it jumped, you will get freeze-ups.

Or find someone familiar with electrical work to re-solder the circuit board inside.

Note that R&R thermostat would require removing the evaporator box from the car, which requires recovering and recharging the refrigerant.

Jon Petersen

Okay, so, next time the AC turns off, I keep the car on and the AC on, and jump the thermostat? And if it works, I know the thermostat is the culprit, and I replace it, correct? If it's not the thermostat, could it be the temperature sensor in the engine bay, or the compressor or condenser relays? If so, how could I tell?