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Pressures for 1993 Cadillac STS - V8 Northstar

Bob B on Tue August 28, 2007 4:49 PM User is offline

Year: 1993
Make: Cadillac
Model: Seville STS
Engine Size: V8
Refrigerant Type: R12

Can anyone advise low and high side pressure for 1993 Caddy -STS Northstar 8 Engine?
System is R12.

Bob B

mhfd112 on Tue August 28, 2007 5:08 PM User is offline

Do you have a little more information? What is the ambient air temperature in front of the car, What kind of engine rpms, are the windows all rolled up?

Bob B on Tue August 28, 2007 5:29 PM User is offline

Air temp would be 100 F. RPM = 1500

Bob B

iceman2555 on Tue August 28, 2007 6:08 PM User is offlineView users profile

Pressures are a diagnostic that the system is fully pressures and let's see what happens. Pressures alone are not a true indication of a completely recharged system.

The strongest reason for the people to retain the right to keep and bear arms is, as a last resort, to protect themselves against tyranny in government.
Thomas Jefferson

Edited: Tue August 28, 2007 at 6:08 PM by iceman2555

NickD on Tue August 28, 2007 6:24 PM User is offline

Have to check my manual to see if they even post pressures, don't think they do, just say charge by weights, but will check. Are you getting a service AC soon light or is it kicking into Econ by itself?

Bob B on Tue August 28, 2007 6:39 PM User is offline

No indicator lights. Just air is not as cold as it used to be at idle rpm. At higher rpm, air is ok.

Bob B

NickD on Tue August 28, 2007 7:38 PM User is offline

Typical pressures for R-12 at 100*F are between 33-47 psi as the humidity increases from 20 to 90% and high side will vary between 275-325 psi

I topped off mine at 85*F at 1,500 rpm, but paying more attention to the evaporator outlet versus evaporator inlet differential temperatures, got around 27 psi low side and around 210 high side. Can also have blend door problems, but check your evaporator inlet and outlet temps first, should be about the same and cold. If output is warmer does show signs of a lower charge, but work that in conjunction with your pressure gauges in case you have other problems.

Course, the system has to be cleaned first, fins, fans working properly, that is the hard part.

Chick on Tue August 28, 2007 7:47 PM User is offlineView users profile

I know it's hard to get at, but with the engine off, try to spin the outer hub of the compressor with one finger..If it spins, your suction valves (reed valves) are on the way out..Will also show a higher than normal low side pressure..So get the pressures once you try the spinning of the hub..Hope this helps.

Email: Chick


Freedoms just another word for nothing left to lose

NickD on Tue August 28, 2007 8:05 PM User is offline

Ha, it's easy to get at, after you crawl under the car, didn't have that problem in a 50's - 70's Caddy. Caddies method of checking the charge is to use their charging station, just recover, add R-12 to the 2.42 pound mark and dump it back in.

Bob B on Wed August 29, 2007 11:18 AM User is offline

I believe that you have hit it with the suction valves being on their way out as the LP side is 45-50 PSIG at 1500 RPM.

Nick D:
What type of system do you use for recovering and reusing the R12?


NickD on Wed August 29, 2007 11:49 AM User is offline

45-50 PSIG at 1500 RPM can be considered near normal at higher humidities and at 100*F ambient temperatures. What really tells the story about compressor problems if you get a corresponding decrease in high side pressures. Have a feeling you are using one of those kit low side only gauges, is this feeling correct?

Been reading about GM charging stations for over 40 years now and thinking of ways to work around it, just a DIYer like you. If GMTech didn't live so far away, would borrow his, or heck, even pay him a couple of bucks to do the work. Even a couple of bucks more if I can ride one of his camels.

Just have the basic tools, thought about buying a recovery station, but haven't ran across an AC system yet that needed work that had anything left in it to recover. When I do, will buy one.

Bob B on Wed August 29, 2007 1:24 PM User is offline

Nick D
I do have the standard double gage set, in fact I have 2 sets. Been using them this type for 20 years or so.
I have not checked the high side of the Caddy yet but will do so.


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