I finally have my car running, after being down more or less for the last 2 years. Now I’m working out the kinks and odds and ends. One I need some help with is the A/C.

When I turn it on, the compressor never engages. I have checked both fuses and the relay. It appears that the ECU never sends a signal to the relay by the ground to the coil side of the relay. I hooked up my laptop to the Datalogit and can see that when I turn on the A/C, the ECU doesn’t think that it has been turned on. I can remove the relay and manually jumper it to make the compressor engage. When I do that, everything sounds and looks right, and it is pumping air into the cabin at 52 F.

When I forced it to run, I checked the pressure on the low side of the compressor, and it was at 35 PSI. From everything I have been able to find searching, that is too high. My first thoughts were that it was the high pressure switch is keeping it from coming on, but from looking at the wiring diagram, it looks like that would disengage the clutch, but would not kill the signal to the relay.

So, is 35 PSI on the low side too high when it is running, and is that high enough to completely keep the compressor from ever coming on? If so, is there some mechanical problem that could be causing this, or did the last place that filled it up get carried away? If not, what would be preventing the ECU from signaling the relay to turn on?

 

does it work on other fan speeds? the ac button lights up correct? people have had problems with the voltages from the ac and fan switches working with the pfc. 35psi is in the neigborhood at idle. the pressure is ambient temp/humidity dependent

 

Okay, after ruling everything else out, I put my original ECU back in, and the A/C works perfectly. Obviously, the PFC is causing the problem. I read where others have had the same issue, but everything I read indicated that the problem only showed up with some fan settings. Mine doesn’t work at any fan speed. I read a couple different suggestions on how to work around this. Are there any that have worked out better in the long run or that were later found to be problems only to switch to another fix? Thanks…

 

From what I understand. the root of the problem is the fan switch itself. The stock ECU is more tolerant of resistance in the switch than the PFC. Some have had luck taking the switch apart and cleaning the contacts - might be worth giving it a whirl.

Dale

 

/\ worth a try. if not a new unit should do the trick

 

Anybody know what resistances should be read at each setting?

 

Very low to zero. I know there was a good thread on the PowerFC forum about it - I think one guy had over 10 ohms of resistance, cleaned the contacts, then had less than 1 ohm.

Ideally, you should have no resistance in the circuit, but whenever you bridge a physical connection you're gonna get some resistance.

Dale