1994 z28 m6. Well my ac has not been turning on for awhile. I replaced the expansion valve, reciver/dryer, and low side pressure switch. I was hoping that would fix the problem, but no it didn't. So I go to diagnose itsome more and find that my a/c relay is not getting the ground signal from the ecu. I've ripped apart the wire loom to see if it was a frayed wire, but it isnt. Also I tested the pin out of the ecu to see if it was giving the ground for the relay, and it wasnt. If I bypass the signal for the relay and hook up a ground to trigger the relay everything works. So for the moment I have a manual switch on for engaging my relay. Thats probably a bad thing since I don't think the computer has any way of cycling the ac clutch.

So my question is, where else could be the problem? When I turn on the AC the 2nd fan turns on, so I know the hvac controls are throwing out some kind of signal. What other signals does the ecu need in order to turn on the AC clutch?

I have about 1.6 small cans of freon in there and don't want to run the risk of it over pressurizing and blowing my seals, or worse locking up my ac compressor and throwing my serpentine belt.

anything?

 

Reset your PCM.

 

ok let me reconnect the ecu wire and see if that works. I never really thought about that. I'll give it a whirl on monday.

 

To my knowledge, only 93s have low side pressure switches, the one you are thinking of is the HIgh side pressure switch which will tell the ECU not to send ground signal to the relay if there is too much pressure, you think maybe its overfilled already?

 

well I tried resetting the ecu. I let it sit for about 30 minutes while I checked out some sweet dvd that Lotus sent me. Hooked up the battery and bam, nothing.

Maybe it is the high side switch. I tested it to see if the 5v reference is going to it and it is. The ground is also good. The only thing I couldn't test for was the reference the ecu will see because I didn't have enough time to find out what pinout the reference was on the ecu.

After looking at a haynes manual wire schematic, it looks like there is a temp sensor bonded to the evaporator? Maybe a bad signal from that would make the clutch not engage?

 

Mine did that last year when I was messing with it. I could run a jumper wire across the common and NO terminals on the relay panel, and everything was good. I plugged in the relay, and the ecm wouldnt power it. I fixed it by plugging the relay in just a little bit, leaving the terminals exposed, and then jumping the common and NO terminals (was either that or I applied a ground to the coil, cant quite remember which). When I removed the jumper, the compressor stayed on, and cycled just fine. Everything worked good after that. I have no idea why the hell that worked, but it did. Try it

 

Does yours have a WOT disconnect?

 

No WOT disconnect. I just flip the switch off when I want to mess around. Usually I'm in traffic or cruising on the freeway when my AC is on.

I wonder what would happen if my system over pressurizes. What would go first? Probably a seal before the compressor right?