samneric Posted June 9, 2008 Share Posted June 9, 2008 Hi all running older cars with retrofited A/C systems... I have just upgraded the A/C in my 4WD Brat to R134a (after a few teething troubles) and wanted to confirm the operating pressures that people are running theirs at... The Haynes book says Low: 28, High: 250 Mine is running about Low: 35, High 250. The sticker on the back of the compressor mentioned a high of 425 PSI - maybe that was just for testing.. Anyways, with the switch to R134, was wondering what people are running with... Steve Quote Link to comment Share on other sites More sharing options...
presslab Posted June 10, 2008 Share Posted June 10, 2008 In my ea82 I run ~20 lbs low side, fast idle, at 80F ambient. Much more than that and the compressor cycles too much. In a retrofit, R134a should be run at a slightly lower pressure. It's been in the 90s here lately and the AC is working great. You can't really use the sight glass anymore.. The old oil will make it look milky even at the correct charge. Quote Link to comment Share on other sites More sharing options...
samneric Posted June 10, 2008 Author Share Posted June 10, 2008 In my ea82 I run ~20 lbs low side, fast idle, at 80F ambient. Much more than that and the compressor cycles too much. In a retrofit, R134a should be run at a slightly lower pressure. It's been in the 90s here lately and the AC is working great. You can't really use the sight glass anymore.. The old oil will make it look milky even at the correct charge. Yeah, was wondering why my sightglass was milky - was gonna read up on that today... One question - can you buy dryers with the pressure switch holes already included or do they have to be tapped? Every dryer I have found online just has the inlet and outlet connectors - no ports for the pressure switches. I've just been running with the switches jumped and will check the system periodically (or when it starts blowing warm!). Steve Quote Link to comment Share on other sites More sharing options...
presslab Posted June 11, 2008 Share Posted June 11, 2008 I don't know about the dryer. I didn't replace anything when I did mine. Quote Link to comment Share on other sites More sharing options...
scrounge Posted June 12, 2008 Share Posted June 12, 2008 One question - can you buy dryers with the pressure switch holes already included or do they have to be tapped? Every dryer I have found online just has the inlet and outlet connectors - no ports for the pressure switches. I've just been running with the switches jumped and will check the system periodically (or when it starts blowing warm!). GM cars from the `80s use a low pressure switch that screws onto an extra schrader valve on the evaporator. If nothing else, you may be able to adapt a GM pressure switch to the harness and screw it on to your low pressure port. They're adjustable by a screw located between the spade connectors: I've adjusted at least 3 down to the correct R134a pressure on my old Oldsmobiles. Ask for a low pressure switch for a 1987 Oldsmobile Cutlass Supreme (RWD) with the 3.8 V6....Or just about any other GM car between 1978-1987 or so. Quote Link to comment Share on other sites More sharing options...
ShawnW Posted June 12, 2008 Share Posted June 12, 2008 I drove my Turbo Brat today and was pleased that the AC (134A) actually works, and WELL, even with the T-top glass letting a lot more sun into the cabin it kept me very comfortable. Sorry I dont know what pressures they charged it to though. Quote Link to comment Share on other sites More sharing options...
Hondasucks Posted June 12, 2008 Share Posted June 12, 2008 That 425 psi is probably the pressure at which the overpressure valve blows. Quote Link to comment Share on other sites More sharing options...
Durania Posted June 12, 2008 Share Posted June 12, 2008 I drove my Turbo Brat today and was pleased that the AC (134A) actually works, and WELL, even with the T-top glass letting a lot more sun into the cabin it kept me very comfortable. Sorry I dont know what pressures they charged it to though. The t-tops make me into a baked chicken when I get out of my Brat everyday. Quote Link to comment Share on other sites More sharing options...
samneric Posted June 12, 2008 Author Share Posted June 12, 2008 The t-tops make me into a baked chicken when I get out of my Brat everyday. Finger Lickin Good? I'm about to put my glass covers back in place. Bought some black tape to fix them up properly. Will post pics when done if you want.... Steve Quote Link to comment Share on other sites More sharing options...
samneric Posted June 12, 2008 Author Share Posted June 12, 2008 I drove my Turbo Brat today and was pleased that the AC (134A) actually works, and WELL, even with the T-top glass letting a lot more sun into the cabin it kept me very comfortable. Sorry I dont know what pressures they charged it to though. Tis ok, I'll go off the 20 PSI low side recommended earlier when I get my new compressor / dryer and expansion valve installed. I am driving around with the glove box out and I'm impressed by the vacuum actuator that operates the interior/exterior air flap. My gf suggested I fit a piece of clear plastic over the glovebox with some hints of neon lighting inside and really "pimp out my ride" Steve Quote Link to comment Share on other sites More sharing options...
samneric Posted June 12, 2008 Author Share Posted June 12, 2008 GM cars from the `80s use a low pressure switch that screws onto an extra schrader valve on the evaporator. If nothing else, you may be able to adapt a GM pressure switch to the harness and screw it on to your low pressure port. They're adjustable by a screw located between the spade connectors: I've adjusted at least 3 down to the correct R134a pressure on my old Oldsmobiles. Ask for a low pressure switch for a 1987 Oldsmobile Cutlass Supreme (RWD) with the 3.8 V6....Or just about any other GM car between 1978-1987 or so. Thanks for the advice.....Will look out for one.. As for fitting, I have just ordered a new dryer with a 1/4" service port. I was thinkin of getting some kind of tee-fitting but with 3 extra ports (kinda like a cross) so I can hook up the high/low shut offs and the main fan control switch. Recon that will work? The main fan control is currently welded into a copper tube from the cond to the dryer (obviously some kind of custom job). Steve Quote Link to comment Share on other sites More sharing options...
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