1997 Burb - Charging A/C and Cooked Something

[1972RedNeck]

I was helping my brother fix the A/C on his '97 Burb (2500 4X4 7.4L). The A/C hasn't ever worked since he got it as the compressor seal was leaking and the PO never bothered to fix it.

Anyways, we flushed the system, put a new accumulator and compressor on it and vacuumed it out for a couple hours to see if it would hold (which it did) and then proceeded to charge the system.

Since the system was empty, we had to jump the low pressure switch with a piece of wire to get the compressor to run to get some refrigerant sucked in. This worked well (always does) for about 45 seconds and then the compressor kicked out. Turns out we were no longer getting power to the low pressure switch even though the A/C light was still on as was the blower. Slightly befuddled, we took a jumper wire from the positive battery terminal to the black/white wire at the pressure switch to see if we could make the clutch engage this way or if something else was wrong.

As soon as the hot jumper touched the black/white wire, the engine died just like you shut the key off. Cranked on it and it wouldn't start. Fuel pump is running. unhooked the battery cables for 5 minutes and tried again. Still won;t start. Swapped ECM's with Dad's '96 Burb. The '96 runs just fine on the '97's ECM but the '97 still won't start. With the '97 ECM on the '96, the A/C won;t work. Swap the '96 ECM back onto the '96 and the A/C works fine. The '97 still won't start.

All the lights and gauges on the dash of the '97 work fine but the high beam and turn signal indicators are constantly on when the key is on.

We're at a loss of what we did and what we need to do to fix it.

Thoughts?