Not sure, bought a rebuilt w/lifetime warranty. Would assume, and you know where that gets us, it was recently.

Went here... https://www.fs1inc.com/

Did the AC work before or right after the rebuilt PCM?

George

No. Has never worked correctly.

However, if I provide the ground to the A/C relay, it works fine. 40 Degrees at the vent.

Based on everything in this thread I think that you may have a PCM ground problem. Most PCM/ECM's have several ground lines coming out of them, I wonder of one of them has no continuity to ground?

George

Possible. Which ones are grounds?

As with your AC wiring I cant find the ground distribution for the 4 cyl engine only the 4.3L In the even that they are the same - there are either 2 or 3 grounds all black with white stripe on: pin18 or 60, 64, and 15 or 64.

George

George. All grounds are good.

I give up. Installed a toggle switch that puts a ground on the compressor relay. Works, drove it around yesterday. That little 2.2 sure works hard with the A/C on, can tell a lot of the power goes to the compressor. But, it doesn't take long for the cab to get nice and cool, can make it cold enough to need a jacket too.

Thanks for your help. Does bother me we couldn't fix it right but i'll take what we have and enjoy.

You sure have done a bunch to properly diagnose this problem. I have one thing left in mind for when you get a break from this and want to try again.

The only thing left that I can think of is the connection from the PCM input to the relay energizing coil, the spot you have connected your toggle switch to (I think). Since grounding that relay pin turns the compressor on, have we checked if the pin on the PCM goes low as it should? If so then that connection needs a new run or needs to be repaired.

George

Yes, that is where I tapped into the wirig harness to provide the ground for the relay. My meter showed 13.85 volts there, never got the ground potential.