A/C pressures?

[iNomis]

I'm checking my 91 535 for R12. Is 100 PSI static and 25 PSI low side within range? Ambient temp was 90. Going to check the high side when it gets cooler out as my gauge only goes to 200 PSI. Should high side be 2.2 to 2.5 ambient temp?

Karl

[Tiger]

Forget about high side... will blow your gauge... 300+ PSI. You said R12? R12 requires about 70 PSI low side. Whereas R134 is around 45 PSI max. Static pressure means nothing unless you got something really wrong with system. The pressure reading is with the compressor running... not when it stop.

[Unregistered]

You need to get a high side guage, they can be found at parts stores for about $15. You are correct that the high side pressure should be about 2.2-2.5 times ambient temp with the compressor running. NEVER set freon or R-34 levels using a low side gauge; this is how compressors get ruined. If you do a search there are some A/C boards with lots of information.


Cary

[Bellicose Right Winger]

Here's a pressure temperature chart for R12 & R134.
http://www.delanet.com/~pparish/pt-table.htm

Your low side pressure of 25 psi corresponds to an evaporator temp of about 26F. This is on the low side of normal and "may" result in evaporator freezeup or frequent cycling of the compressor. Evaporator should be in low 30 psi range to operate as cold as possible without freezing. You may have a low refrigerant charge, a bad expansion valve or a bad gage on your manifold. As noted by others, don't attempt to recharge based on evaporator pressure. How does the AC perform and how does your sight glass look?

Paul Shovestul


I'm checking my 91 535 for R12. Is 100 PSI static and 25 PSI low side within range? Ambient temp was 90. Going to check the high side when it gets cooler out as my gauge only goes to 200 PSI. Should high side be 2.2 to 2.5 ambient temp?

Karl

[.Loke]

How do I know my AC is working as it should. Dumb question perhaps, but I seldom use my AC as I live in Norway. But those few days I do use it, it gets cold all right. But I have no idea when the system was recharged and if it is operation as it should. Any guidelines or checklist? And is it true that the compressor wont start if its too little R12 in the system?

[Tiger]

Compressor will not run if freon level is too low. If your A/C work fine during the hottest time... cold air all the time... no warm-cold-warm... then you are fine. R12 is very hard to get and if your mechanic has it... he is the only one who can put it in.

[Tiger]

I got the pressure rating wrong... I have to go verify it again later...

[iNomis]

Here's a pressure temperature chart for R12 & R134.
http://www.delanet.com/~pparish/pt-table.htm

Your low side pressure of 25 psi corresponds to an evaporator temp of about 26F. This is on the low side of normal and "may" result in evaporator freezeup or frequent cycling of the compressor. Evaporator should be in low 30 psi range to operate as cold as possible without freezing. You may have a low refrigerant charge, a bad expansion valve or a bad gage on your manifold. As noted by others, don't attempt to recharge based on evaporator pressure. How does the AC perform and how does your sight glass look?

Paul Shovestul
I was able to test the high side pressure and it barely moved over what the static pressure was (<100psi). I assume that means I have a low charge. A/C is blowing barely cool. Where is the sight glass?

I think I'm going to go ahead and order the r134 conversion parts and convert it. Anyone have any ideas on where to rent a vacuum pump?

Karl