High Pressure issue R4 Compressor Chevrolet Tahoe

[1slos10]

I recently swapped a 5.3 LS Motor in my 94 Tahoe, and at first I had a line kinked and the compressor wouldn't stay engaged. I fixed the kink and recharged the system and now when you start it up after it has sit for a little bit the high side pressure will go up to 450 and disengage the clutch until the pressure drops back down then it re-engages and goes back up to 450 and disengages. It'll do this for a few minutes and once I drive a little ways it starts acting normal low side around 45 and high around 245. And it does fine the rest of the time, idling, parked or driving. Only does this at startup. Compressor is 6 months old, along with condenser, accumulator and orifice tube. Any ideas? Could it be air in the system?

Thanks,
Ronnie

[bohica2xo]

Condenser airflow issue.

Fan type?

[1slos10]

It has twin electric fans

[1slos10]

The fans don't turn on until 185 degrees, and the pressure stabilizes before it gets over 120 degrees, usually a couple minutes after it starts. Could it be the orifice tube stopping up possibly?

[71403]

Fans should be controlled by the high side pressure and/or state of a/c request not just engine temp.

Is the LS engine PCM controlling the fans?

[1slos10]

That is correct, the LS pcm turns the fans on, and the wiring for the a/c is from the 94 harness and does not cut the fans on with a/c signal. Even if the truck is warmed up and the fans come on when starting, it still doesn't keep the clutch locked in. It goes through the engage disengage back and forth for a few minutes regardless of fans running or not.

[1slos10]

One of the guys at the shop said he had to go through the evacuation, vacuum and recharge process a couple times to get air out of one he was working on. It was a Robinair unit but I'm not sure of the model number. Could this be air in the system or not likely?

[71403]

Multiple passes "to get the air out" doesn't sound right. Overcharge, high side restriction, air, all good candidates.

Had a '96 GMC doing very similar to yours and it was an overcharge. (3.5lbs recovered from a system spec'd at 2lbs)

[bohica2xo]

If the fans don't run with the compressor it is not right. You can let it ride the HPCO until they do, but eventually that will cost money.

The 1994 trucks all had mechanical clutch fans. Fix the electrical error that is keeping the fans from starting with the A/C compressor command as GM intended.

Any shop that needs 3 tries with an automated charging station should be avoided in the future.

[GM Tech]

ditto on the fan issue- you MUST have fans on immediately when a/c is on.....case closed.