I've been reading several forum posts on AC pressure issues. I've read at least two post that come close to the situation with my 98 expy:

1) My the Compressor come on (I hear the click and to load on the engine changes)
2) My LOW-SIDE pressure is Over 100 psi (in the RED) which cuts out the compressor, then the pressure drops and the the cycle start again about every 1-2 seconds.

From what I'm reading my Compressor is bad. I have the shade-tree version of a gague for checking if more refrigerant is needed and therfore only have low-side readings.

So my question is: With the condition above is it advisable to even bother getting a high-side gauge set since the compressor is gone or can it be something else?

Thanks for any light that is shed on my problem....

 

Typical on most auto a/c systems, it should cut out around 23psi on the low side, and the problem you descibe, it could be cutting out on the high side.You need more info, does the gauge move at all, is the pressure rising when it cuts on? To be perfectley honest, you need both gauges to evaluate the problem.Hope this helps.

 

Low side gauge does move. It climbs to RED zone when compressor on the over a second or so, to the GREEN zone drops, when compressor cuts out. When in the GREEN zone the compressor kicks on again. Let me know if this helps. I will be looking into a gauge set tomorrow. Thanks on any information you can provide with what I have so far.

 

When you get the gauge set (manifold) tomorrow, we'll have a better understanding of what's going on. Actual pressures make things a bit easier. With 134A, you can't cross up the connectors, and we need to know what the high side is doing. Has the A/C worked in the past? Is the vehicle new to you, there are plenty of shady dealers out there.Looking forward to hearing back from you.

 

By the way, if the gauge is moving, the compressor is pumping. Get the high side reading, because the pressure on the low side will climb a little once the cycle starts, then pulls down. If it doesn't stay running long enough due to the high side cutting out, it will be hard to determine a problem.

 

An initial low side pressure of 100 psi is not abnormal if the compressor is not running and the underhood temps are high enough. Once the compressor engages, the low side should drop and continue dropping down to around 20-25 psi. At this point, the cycling switch should open. The pressure should rise to around 45 psi, at which point the switch should close and the cycle should repeat.

It is impossible to accurately diagnose a failed compressor with only a low side guage unless the compressor is completely blown. That's why the high pressure is also needed. FWIW, I'd be suspicious of the accuracy of the cheap guage you're using and that you simply have a system with a low refrigerant charge and you're simply seeing inaccurate readings.

The cycling switch does not have a high pressure cutoff point. It should close at around 45 psi and remain closed (unless failed) until the pressure drops to the low pressure setpoint, around 20-25 psi. There is a high side cutout safety switch that should disengage the compressor and engage the high speed fan, but it has a very high cutout point, somwhere north of 400 psi, IIRC, don't have my manuals handy...

When you get the manifold guage set, make certain you follow the requisite setup procedures in the manual and that you properly adjust for ambient conditions.

Steve

 

Thank you, both. I'll be getting the gauge and manifold set this week. I post the findings.

 

We need to know what your ambient temps are when you are doing the test.Pressures go up with temps. With the ac off and 100 deg outside the static pressure hi and low side will be 100 or more if I remember correctly. When the compressor comes on the low side should do the 25 to 45 as said above. The high side will give you an indication of whats going on. If the compressor is short cycling on and off and the high side is low say close to static low side then you have a low charge. You need to charge until duct temps are near 40 and compressor suction at the compressor starts to get cold. At 60f high side should go up to 135-150 psi at 100f 175-190 or so

Dick

 

I had the same problem!! My R-134a was 2 lbs!!!! low. When the dealer charged the system the problem went away. I now have a fully functioning "Blend Door" that i replaced myself on a Saturday (8.5 hrs) and blowing cold with the A/C charge!!!

gets hot here in the ATL..need that A/C

 

as others have said, you need both a low and high side gauge,
when the compressor comes on , the low side should drop, and the high should increase, therefore indicating the compressor is pumping.

I work on commercial refrigeration, not automotive, and am not sure that automotive systems have a high side safety cut out, but if your suction comes up that fast, you could have bad valves in the comp.

one other word of advice, if you end up recharging the system due to low charge, first you need to find and repair the leak, then once repaired, get a vacuum pump and pull a good vacuum, then recharge with the reccomended weight of refrigerent as per mfg. specs.

it still cant figure why auto parts stores can sell refrigerent, as in the trade, we are subject to big fines for knowingly venting it into the atmosphere.

Bill

 

I never understood it either, I have my universal, and the automotive add on, and it seems anybody can purchase the refrigerant (134A) and not be bound by the restrictions we deal with.I would hope people don't vent, but the shade tree mechanic,as we know, probably are old school. What they don't see, they won't know.

 

R134a is supposed to be harmless to the atmosphere, but it's still not allowed to be vented under EPA regulations.

Doesn't make any sense to prohibit venting if it's supposedly harmeless.

R12, R22, etc, OTOH, are regulated.

See what happens when politicians get involved?

Steve

 

It drives the cost of doing business up, and ufortunantley, we have to pass the cost onto the customers. R-404A (HP62- Low Temp) is the same as 134A( HFC)and it's regulated as well. How is the Puron sales going in your area. I wont use it, the applications seem way to high (pressures). R 22 for residential is still avaliable till 2020.Are you using any other replacements for 22?

 

should the pressure on the low side be 100 psi when the car is off?

 

If the temp is near 90-100 yes. Or if you just shut the car off. The pressure of the freon is directly related to temperature.

http://www.csgnetwork.com/r134apresstempconv.html


Dick