MikeS

Anybody know what kind of pressure either side of a car A/C system are?

rezinn

I want to say 110 psi on the high side from what I remember when doing my a/c this summer. For the low side probably a little less than half of that if filled completely.

82camaro

High side can vary from car to car. I usually fill them to 40-45 psi on the low side(compressor running).

MikeS

I'm wondering since the high side gauge on manifold gauge sets goes up past 400psi. I want to check the pressures in my system, but don't quite want to buy a gauge set. Just wondering if i've got anything that I could use already.

RB83L69

It depends on how much Freon is in the system, what the outside air temp & humidity is, how fast the blower is blowing, engine RPM, car speed, and a number of other factors; but it's tpically anywhere from 225 to 375 psi in normal operation. At 90° outside air temp, 60% RH, sitting still, 2000 RPM, Max A/C function & max blower with the doors open, expect about 325. It is so variable that on a working A/C I don't even usually bother to hook the gauge to it, because it isn't very informative, and because a bunch of liquid Freon usually escapes when removing the gauge.

Like the other post said, the low side should be 40ish.

rezinn

Okay I'll concur with about 300. I was wanting to say that but I remember seeing 110 on my car earlier. I guess that is inaccurate since my freon leaks out anyhow.

Vader

High side pressure can go higher under heavy loads on hot days. The high pressure cutout is set to open at 375 or 425 PSIG IIRC. R134a replacement refrigerant will run at a higher pressure than R12, and that should also be a consideration in selecting a replacement refrigerant.

cp87GTA

WHAT are you guys working on?? Refrigerant 12 at 90 degrees, standing pressure is 99.7. Providing liquid is pressent. High side pressures shouldn't be more than 180 psig at 95 degrees. Refrigeration pressures are varible, they will change as the ambient temps change. If you charge at say 75 degrees ambient air temp, high side should be about 135 psig, low side should be 37 psig. Those figures are with a CLEAN evaparator and a CLEAN condenser. 134a will run a few more lbs. psig. The #s on a manifold set will tell you every thing. You should NEVER charge a refrigeration system without the high side hooked up. They put those TWO gauges on there for a reason. The high side will tell you if you have a faulty compressor, condenser, tev, or evpansion valve

MikeS

Basically I'm just trying to diagnose a few problems. Vader suggested taking my high and low side pressure readings with a manifold gauge set. I don't own one, can't think of anybody who does, can't quite make myself buy one, and want to know if any other gauge I've already got will do the job. Yeah, I know, I know... I need to just swallow the cost and buy the gauges.

82camaro

Sure hooking up the high side can tell you some stuff if you need to diagnose. Back in the old days of R12, when you get it in a small can all you needed was the can tapper to put in the freon--no guages at all. Just put in enough so the air is cold and the compressor kicks in and out at a slow rate or not at all.

cp87GTA

Pretty hard to dianose a refrigeration system WITHOUT a manifold set. You have to see what both sides are doing, to find out where the problem lies. One problem may be moisture in the system. That could form ICE and plug up the expanion valve. If the car in question has been sitting with no refrigerant in it, that's a good chance. If it hasn't had the drier changed, and evacuated properly.