I put a brand new A/C system in my 98 Z28. While charging the system, the compressor would not kick on. I jumped the A/C compressor at the relay to take the charge. Pressures are dead on, good vacuum, no leaks, showing 41 degrees from the vents. The compressor will not kick on without jumping at the relay. Jumpering at the pressure sensor also did not turn on the compressor. I put a brand new relay... no good. I replaced the pressure sensor with a brand new AC Delco, no good. On the relay, we tested the 4 plugs for the relay. getting 12v to two plugs, a solid ground to one and not getting a solid ground to the other. I know the PCM sends the ground, my radio clock is working properly. I checked all of the wiring and pins on the PCM, all look good. I also checked and cleaned all grounds to block and body. Anyone got any ideas, please help.

 

Have you scanned the PCM for A/C related codes? In general, they do not turn on the SES light.

 

Yes. Getting high voltage to pressure sensor. At the same time, my fuel level sensor stopped working and my hs fans stay on. All started with a loose negative battery cable.

Yesterday I chased all of the wires from the pigtail to the PCM pins. All of the wiring is good. The system works when I manually supply a ground. I think I narrowed it down to the PCM. I'm gonna see if I can get my PCM repaired or reflashed, or just get another one. My car is a 98 so they are little harder to find. Ill post an update, thanks for replying.

 

If you have a code for the pressure sensor, it could be preventing the PCM from turning on the A/C. I have access to a 98 shop manual. I'll see if it explains the logic for the system.


[EDIT]
The following conditions will prevent the PCM from grounding the clutch relay:

-high coolant temp
-low A/C system pressure
-high A/C system pressure
-wide open throttle
-high engine RPM

The codes do not have to be active. Even a 'stored' code will prevent the PCM from supplying the ground. Clear the code.

 

I did a manual reset (pulled PCM Ign, PCM Batt) w/ key on, waited, etc. Did not help. And with the fuel level sensor going out at the same time, and what caused it to go out, we pretty much narrowed it down to a shorted pcm. I'll let u know when the new one gets in, thanks again.

 

hey injuneer, would those conditions apply to an 02 as well? i think its pretty cool that the A/C doesnt work when youre driving hard (in the case of high rpm or WOT)

 

PCM was the problem. I ordered a used PCM from that madtuner guy, he flashed in my VIN, I hooked her up, gas gauge works, A/C works, life is great!