Anyone know what conditions must be met for the PCM to close the circuit to the A/C relay?

 

The pcm needs to see a/c request and at least 40psi refrigrant pressure to get started. Everything else shuts the ac clutch off after it is running (high pressure, <36 degree evap, high throttle position etc). I just recharged mine with an autozone kit so I went through all that.

 

It doesn't need to see cooling fans or anything? After I did the motor swap, I went to have my A/C evacuated (air) and recharged and the clutch wouldn't kick on. I ran the car with the A/C on and checked the voltage on the connector to the compressor. No voltage. The clutch wouldn't kick on when they were trying to recharge it, so there was pressure then. I need to get this thing working, its like 800* in FL.

 

Ok, now I see. I had the whole system pumped down and recharged when I reinstalled my motor. However, they should be using a machine that handles both the low and high side of the system and they don't require the compressor to be on. If you have leaks they will not charge. Did they get any charge in? With a scanner you could check the pcm readings for the a/c charge and you could check for code DTC 61 "low a/c pressure". If you must, jumper the red wire to the grey wire on the a/c pressure switch to trick the PCM to think you have enough pressure to turn on the clutch so you can add refrigerant.

 

Yea, they evacuated the system, and then started adding to the low side but the compressor wouldn't kick on. I don't have access to a scan tool, its a 94 LT1 in a 95 car, so it has the OBD II plug, but the system is OBD I. No one has an OBD I scan tool, they just try to jump pins and flash the code with the SES light and don't believe me that you can only do that with 93s. Maybe I need to add refrigerant up to 40psi and then reset the PCM?

 

Yes, once you get the pressure above 40 psi, the code will go away. You need to jumper the switch to turn on the compressor to get any coolant in. I doubt your system is still evacuated though. Maybe you could pump it down again and then jumper the pressure switch, turn the a/c on and the hvac fan on high to add coolant. Or, you could take it to a place that has the proper equipment to charge without turning on the compressor. I got my total recharge done at a quick lube place.

 

Well I got it working (sorta). I had the compressor resealed and a new clutch put on. It was cycling on and off on the way home and eventually wouldn't cycle on at all. It won't cycle on even with the sensor jumped. I had the pressure checked, with my first thought being that it was leaking. 120 psi on the low side. The shop that checked the pressure confirmed my first thought. The seals in the compressor are not sealing and its leaking from the high to the low. Anybody else have any input? I guess I'm just going to have to complain to the shop that resealed my compressor.

It's lovely weather for no A/C...