Some of the older systems did have a bouncing needle on the gauge. I used a set of gauges that had glycinerin in them to cut down on that.

First thing is to verify correct refrigerant charge.

You're asking me to remember a 50 yr old system? If I remember, going backwards from the compressor there is a temp control switch probably controlled by vacuum. Sorry, this is too old for my mind.

It means there is probably no 12 volts getting to the clutch

and do not rule out old leaky hoses.

need to know ambient temp. if it is hot enough, the compressor will not cycle due to heat load. low airflow may cause evap to freeze. tape manifold to windshield and indicate pressures. without checking system, you may have a defective cap tube switch in the evap or it may not be in proper location.

I have a complete of service manuals for a 1998 Astro van. I believe they are the same for a 1999.
I will sell them for $30.00 plus $40.00 shipping. They are complete and heavy

You still need to mist the condenser with a hose. Passages may be plugged internally. Air may flow thru the outside of the condenser but not thru all the passages. I probably did not explain that. Sorry

This is an R12 system. You can try putting a shower cap on the compressor and let it sit. Then after a few hours, put a leak detector inside the shower cap. This system also uses an EPR valve so it is handy to have another low side gauge. I do have gaskets for that system. I would also advise you to...

I personally think you're wasting your time trying to flush that condenser. Corvettes were know for having lousy AC systems to start with. To bring the high side down, mist the condenser with a water hose. If the high side drops like a rock, you have possibly an air flow problem and you're not rejec...