'07 Equinox A/C has gone kaput. How to diagnose?

[Scott2002SL2]

Some my '07 Equinox A/C has gone kaput. I's been working just fine all summer then suddenly the A/C button light started flashing slowly and the cold air went away.

It came on sporadically for a couple days and then would shut off and blow hot air.

I got out my gauges and hooked up to the low pressure port. The compressor was rapidly cycling and pressure was jumping high into the red and then into the blue as it cycled.

I turned of the system and checked all, I think all, the relays and fuses involved and all seem fine.

I released some pressure from the system and the lights, A/C and recirculate, stayed on and the compressor was engaging but not cooling and the pressure was showing very low.

With the system cranked up I added Freon to 55 lbs, it was 85F out, pressure gauge stayed steady at 55 lbs and the compressor stopped, lights wont come on, blower works and blows hot when set to hot and air temp when set to cool.

Now the pressure is at 55 lbs, car on or off, A/C requested or not. Fuses and relays all appear fine, compressor turns by hand but will not even try to engage when asked for cold air.

What the heck is going on? Compressor fried? Some mystery thing?

I saw somewhere I can't seem to find again there is a way to reset the system in cases like this.

Help anyone? Thanks in advance. Peace and Good Health.

[Blue Bowtie]

If you study the T/P curve for R134A, it may become apparent that the equalized pressure at 85°F should be much closer to 95 PSIG, not 55.