Correct pressures for a 1st gen R12 system

[Jason94sport]

I'm looking for the fully charged pressure readings I should be getting with a R12 system, for a 1st gen. Hi & low side. I'm not sure if it's low or not. I have gauges, correct R12 but need the pressure specs. My manual I have does not list them.
Thanks

 

[Jason94sport]

Anyone?
How does 1 check to see if they need freon? I'm not adding any until I can see what's in there & how much I need. I do not want to overcharge it & wind up killing my AC here in HOT FL.

 

[Maniak]

I don't think many of us have ever charged it with r-12.. I know when I charge with r-134, and I don't know how much is in there I more watch the low side and just make sure the high side doesn't go "too high".

for example, on our '92, I try to get it to run 30psi on the low side (and hold at 2000 rpms) and a high side of about 2.5 times the ambient temp (temp of the condenser actually). So, if its 100F outside then before I even start I want to see about 100psi in the system. Once I start charging etc I want the high pressure to be around 250 or so. Normally I end up closer to 275psi since the condenser temp goes up some while I'm charging the system.

Hopefully there is a rule of thumb someone can at least point out for r-12 pressures if no one knows the actual goal pressures are.

~Mark

 

[TOMANDPAT]

All pressures are temperature dependant. At the very minimum, an R12 system should show about 60 psi just to keep the system from freezing up. That's with an ambient temperature of 70 - 74 degrees farenhiet. As the ambient temp goes up, so should the low side and high side pressures. If you don't know a lot about air conditioning system, shoot for a low side pressure of about 70 psi at 80 degrees ambient. Invest in a pocket thermometer and check the ambient temp and the air temp coming out of the center A/C vents on your vehicle. Outlet air temp in the 40 degree range is optimum. By the way, a good thermometer is just as important as a gauge set when servicing the system. To accurately check ambient temp, hold the thermometer in front of the grill so you're measuring the actual air temp going through your condensor.

Tom

 

[TOMANDPAT]

Boy, do I feel stupid. I gave you the wrong info. The minimum pressure for an R12 system is around 30 psi, not 60. I was using my R22 specs. All the rest of the info I gave you is correct, although you want to shoot for around 40 psi at 70-74 degrees farenheit. Sorry for the mistake

Tom

 

[Jason94sport]

Unfortunately the air temp is the in 90's & is going to be for a while.

 

[ranger7ltr]

High side pressures are key...

If you have a high side that is 2.3-2.7x ambient temp on the high side on a properly working ac system should get you a range of 30-50 psi on the low side with a vent temp around 37-42 F...If your high side is higher than that you probably have a weak cooling system or a fan that is not working as well as it should be...

The low side pressures will cycle the compressor off when it drops to the low end setpoint to keep the evaporator from freezing up and when the pressure increases the system kicks the compressor back on to maintain the cooling effect...Generally the low side pressures are indicative of the temperature at the surface of the evaporator...And you want to make certain the humidity drain is open and clear so that any water generated will drain away from the evaporator and not stay in the area to help freeze it up...