A/C pressure question
05-23-2010, 02:33 PM
#1
Race Car
Thread Starter
A/C pressure question
Recently I resealed the A/C and added a new drier and expansion valves. I noticed after a 8 months or so the system lost the r134a. Now I added some but the gauges shows 0 pressure with the system running and jumps to 70 psi when I turn the car off. The compressor is working and I bypassed the freeze swtich. Maybe there is a clog somewhere in the system?
05-23-2010, 02:57 PM
#5
Chronic Tool Dropper
Lifetime Rennlist
Member
Lifetime Rennlist
Member
Gio--
Which side were you measuring?
Depending on ambient temps, the 'resting' pressure on the suction side can easily be 70 PSIG. If the systenm isn't charged adequately, it can also draw down to 0 PSIG or even less when running. If you have a drier with a sigh glass, look to see if there is flow when you run the compressor. In the drier, the flow should be liquid with a -few- bubbles at idle.
Now, if the system drained completely due to a leak, it's quite likely that it drew in some air as it changed temp even if it was just sitting. If that's the case, you'll want to get the air out before you recharge, since air robs a significant amount of system capacity. Of course you'll want to find and fix the leaks first. So find and fix the leak(s), evacuate with a good vacuum pump and leave the pump attached overnight if you can. Evacuate the charging manifold all the way to the charging cylinder using the pump if you can so no air is introduced. Then charge by weight to get it right.
Which side were you measuring?
Depending on ambient temps, the 'resting' pressure on the suction side can easily be 70 PSIG. If the systenm isn't charged adequately, it can also draw down to 0 PSIG or even less when running. If you have a drier with a sigh glass, look to see if there is flow when you run the compressor. In the drier, the flow should be liquid with a -few- bubbles at idle.
Now, if the system drained completely due to a leak, it's quite likely that it drew in some air as it changed temp even if it was just sitting. If that's the case, you'll want to get the air out before you recharge, since air robs a significant amount of system capacity. Of course you'll want to find and fix the leaks first. So find and fix the leak(s), evacuate with a good vacuum pump and leave the pump attached overnight if you can. Evacuate the charging manifold all the way to the charging cylinder using the pump if you can so no air is introduced. Then charge by weight to get it right.
05-23-2010, 04:05 PM
#6
Race Car
So you are saying that low/high when running is 0/150 and rest is 70/70? Sounds like it's undercharged and/or there is air in there. Like Dr. Bob said, you will need to vacuum the system out with a proper vacuum pump and I would also replace the receiver/drier. Then you want to put in the correct amount of refrigerant by weight if possible. An '89 with rear A/C should have 1030 grams of R134A, which is about 36.5 oz. If you are charging using small cans, you *must* make sure to purge the hoses after every can change otherwise you will put in a lot of air.
Dan
'91 928GT S/C
475hp/460lb.ft
Dan
'91 928GT S/C
475hp/460lb.ft
