I have a '93 Aero with rear ac/heat. I just got this last winter and until last week the air didn't work but the compressor did cycle in short intervals. I added one can of R12 I still had lying around and the cycles got longer and the vents felt a little cooler. This week I bought a good gauge and a friend at work gave me 2 more cans of R12 he had lying around. I put the gauge on the low side and started to add more R12. Low side was going up and down good. Before I had a half can more in, the low side quit going down and the compressor quit cycling of course. Now when the engine is hot, air temp 85, ac off, the pressure is around 110 both sides. When I turn on the ac (front only) the high side starts cycling around 150 - 200, then slowly climbs in its cycles. After a minute the cycles are starting at 300 and climbing to 350+ and I shut the ac off for fear of damage. The low side is still in range but never drops low enough to cycle the comp. The vents are still barely cool when this is happening. I get the same results when I turn both front and rear ac on except then the rear vents feel a little cooler and the fronts stay warm. Seems like something clogged but any help on where to start would be great.
Your compressor may be bad or you have a blocked oriface tube.You should check the oriface tube first but you will need to recover the R12 first, don't vent it to the air. Remove the oriface tube all let me know what it looks like.
you can tell if it's the orifice tube without draining the system. Look at the thin a/c tube under the accumulator, the tube that goes into the firewall. If the orifice is plugged you will see condensation up to the spring connector but none on the tube going into the firewall.
If its going into the 300's then the compressor is obviously good. If the orfice tube is blocked, you will see a low side pressure drop in most cases. Check the condesor coil (near radiator) make sure its not dirty. A high pressure on the liquid side could mean several things. One, a dirty cond. coil, too much freon in system, a block orfice (or if equipped) a sticking TXV, or even outside temps too high.
Can you give more info? How hot outside, how hot inside, how much freon you actually put into the system, how much charge the vehicle calls for, etc.
one thing that will always cause high discharge pressure is air and non condensables in your system. those can only be removed with a vacuum pump, being an automotive ac has a very small capacity, it dosn't take very much to cause this. if your suction pressure is low, it is likely a plugged orafice.
in a small refrigeration system, one cant over stress making sure the system is free of non condensables, and also be sure to weigh in the correct amount of refrigerent as the vehicle specs.
I see condensation on the tube going into the firewall. the tube is hot before the connector, and cold after. I think I will have it evacuated and flush and check the orafices. The condensor looks clear if I shine a flashlight through it, nothing looks to be blocking it.
Thanks for the help.