The oil on the hood means the shaft seal is leaking. Some have posted that it leaches through and ruins the paint so you might want to use some Simple Green to clean it off.

Low pressure switch closes at 50 psi and the compressor comes on - depending on where it's set, it's going to open at 22.5 to 25 psi and the compressor will turn off. As the gas sits, the pressure will rise back to 50psi and the cycle repeats itself. To get an accurate reading, you need to keep it running which can be accomplished by jumpering the low pressure switch harness with a paper clip. Otherwise, until it's full, it going to continue to cycle on and off and the gage is going to be tough to read. At 85 degrees, full charge, I'd expect a low of 28, maybe 30 psi max, with no cycling, engine at 1200 to 1500 rpms, a/c on high, windows down, both radiator fans turning.

 

PS: Here's the site I used when I replaced my shaft seal:

http://www.pelicanparts.com/techarti...so_rebuild.htm

Since it's losing oil, the compressor is wearing faster and that puts more metal into the orifice. I was really anxious to see how well my new seal held, so I slapped the compressor back on, pulled a vacuum and dumped in 3 cans of R12. Cycled endlessly until I remembered that the orifice was probably plugged up - which it was - so I lost 45 Bucks worth of gas and started over.

 

OK,I understand now. I need to jump the low pressure switch. That makes sense. I didn't understand why the guage went so high. I'll give it a try again tomorrow and post the results. What orifice are you talking about that clogged after you installed the new seal? I didn't know the vette shared the same AC comp as the 911. My brother is a Porsche guy. This will give me good ammo the next time he rags on my vette! Thanks again!

 

Porsche, Lexus and few of the others use Nippondenso compressors - they're different models, but the internals are pretty much the same and the shaft seal replacement works as shown in the link I posted.

The orifice is a screened restriction at the inlet to the Evaporator. It meters the high pressure liquid refrigerant - making it a low pressure liquid refrigerant - that boils in the Evaporator absorbing heat. To access, you have to discharge and then undo the fitting at the bottom of the Evaporator. Grasp the end with some needle nose pliers and then gently work it out.

Once it's plugged up, not enough refrigerant enters the Evaporator. What does get in boils immediately and there's nothing left to absorb any heat. What gas gets to the outlet has very little pressure and the low pressure switch shuts it down. The high side then rises (it's backed up due to the restriction) and more gets in raising the static pressure (compressor is off) high enough to close the switch contacts (50 psi). It again boils off immediately, so you get the rapid cycling or on/off condition.

Your ECM monitors this cycling, overall pressure and a couple of other things (relay for example) and shuts it down when it senses the pressure is too low. On Electronic Air, you will get a Code 9 out of the Control Panel. You may also get the a/c codes (depending on year and function - 65 to 69 if I remember correctly) which you can pick up on a scanner.

 

OK, I love my car again. That worked and I've got AC for now. I think I'll order the parts for A/C comp seal and give that a shot next. Thanks again Suncr you were a huge help!