I have my dad's 1978 camaro LT, been sitting 7 years almost done with brakes and interior. Mechanically its about good now runs well. I just replaced A/C compressor, accumulator and all lines. I completely vacuumed it out and stayed at about -30 psi for 30 minutes so no leaks. I converted to R134a and charged it uptook a while because the reto fit adapters only fit the low side so i had to put all in as gas. It took about 2lbs. at idle I have 40 psi and air seems pretty cold about 65 degree. but when I increase rpm's the pressure goes way up and compressor kicks off. Can someone maybe point me in the right direction on what I did wrong?

 

It sound like you know what you are talking about. Please do not take offence if I write this to a less technical person. I am taking into account many other may read this .

You are saying when you rev the motor the low side pressure goes up? I assume you can not see high side pressures? This would give us a better idea what was going on inside the system. Did you check the orifice tube? Kind of sounds like your high side is getting to high and kicking the safety regulator which releases pressure back into the lowside at the compressor. If the system continues to build pressure then a high side switch will shut the compressor down. Since its a 78 I am assuming the fan is working? An over heating system can cause all kinds of issues. If you are missing a shroud or have after markets setups add the biggest house fan you can borrow to front of the car while you work on it. Also look to make sure the condenser looks like its getting flow and does not have to many bent fins, dirt or bugs blocking it. When the AC is working make sure you can feel a big drop in temp on the outlet compared to the inlet of the condenser. The inlet being the side coming from the compressor.

It is possible that this is a manufactures defect or the safety regulator inside the compressor, It could also be there too much coolant in the system or you have a partially plugged system. I am going on memory from the 80's. You want to look up the amount of R134 the system should take and what is the normal high pressure kick out switch. There is not great way to test the compressor that I know of. It more prove everything else is working as it should and all that is left is the compressor. High side pressures vary depending on a lot of factors. Outside temps, humidity, efficacy of the system and the charge volume. But after say that if the system is flowing and you have the correct oil/coolant volume then the compressor should not be able to hit its max high pressure without the low falling to well below 25 PSI. (to add pressure you need coolant it needs to come from somewhere) There is simple not enough coolant in the system in the system to build pressure on both sides of the compressor. The only way a plugged system can cause what you described is if you blockage changes the flow of the system and now your low side port is on the wrong side of the blockage.

The easiest thing to do as a DIY guy would be to start dropping the volume of the R134 in the system. The pressures should drop so in theory no matter what is wrong the system should work better.

FYI what ever is going on it is not common. I have not seen this exact situation In 5 years in the 80's every spring I did AC repair. I even had a second bay that was just for recovery and charging system after they where fix, In fact I can only remember one time this even reminds me of. When I was in AC class one of the students brought is his 70 Chevelle that had the AC deleted for al lease a decade. With the teachers direction he bought a new compressor, dryer receiver and all the o-rings but just about everything else came from a local junk yard. After putting it all together and sorting out the leaks with some brazing we charged it up. We could not get the pressures where they should be (I do not remember what they were.) Teacher had us pull the lines and the evaporator core and we benched flushed them. Sure enough there was the black silicate from a broken dryer receiver hard as a rock inside the evaporator. It took a couple of hours with soap and water to get it clean, I have no idea how I would have done it in the car. I would have most likely just replaced it.