High pressure on the low pressure side of the AC System.

This site may earn a commission from merchant affiliate
links, including eBay, Amazon, Skimlinks, and others.

BadgerManBEN

BadgerManBEN

10 Year 15 Year 20 Year
Joined
Dec 1, 2005
Threads
14
Messages
51
Location
Salt Lake City
My AC stopped working so I checked the compressor and it seemed to be working just fine. So I went and picked up some R134a with the gage on it thinking it must be time for a recharge. I plugged it in to the low pressure side, even made sure it was the low pressure side by tracing it out, and the gage read 130psi. If I am right that is 100 psi too high. Anybody heard of this and have an idea what might cause it?
 
Other details that may help. I saw the high pressure and did not try to discharge any freon into the system. It was high pressure with the engine running and while it was off. I let some of the pressure out down to about 100 psi and it went back up.
 
Was the compressor running? If the compressor isn't running the low and high side pressures will be the same, base system charge, about what your seeing.
 
Is the compressor engaged when you're checking it? Look at the front hub of the compressor, not the pulley, and see if it's spinning. If not, then the pressures will be even on both sides of the system. By the way, those hose gauges are notoriously inaccurate.
 
I had my AC converted to R134a in my FJ62. It wasnt until my AC went out a second time did we realize the fittings were flopped from the conversion (hi pressure fitting was actually the low pressure side and vice versa). I do believe the AC shop was able to insert freon into the hi pressure fitting side....
 
dixie_cragger said:
I had my AC converted to R134a in my FJ62. It wasnt until my AC went out a second time did we realize the fittings were flopped from the conversion (hi pressure fitting was actually the low pressure side and vice versa). I do believe the AC shop was able to insert freon into the hi pressure fitting side....
Click to expand...

Yep, you can fill on the high side. With the engine off, turn can upside down and fill as liquid.
 
Knowing how these compressors don't internally disintegrate, I'd recon the expansion valve is stuck open. 130psi is a bit much when the pressures are equalized with the system off, so this tells me the compressor is pumping. That is unless your ambient temperature is really high. Put a real set of gauges on it and holler back. The valves in the compressor could be shot, but not likely.
 
If this was the gauge that comes with a can for around $15-$25, its junk. I return about as many of these as I sell. I would not add or release anything untill you check it with a real set of gauges. Just me experience.
 
"Balancing" in A/C biz

The term "balancing" is a term sometimes used in the refrigeration business that referrs to adjusting the level of charge. It's a pretty arcane term, but it's more accurate than "charging" since sometimes the system is overcharged. A refrigeration system is properly charged by adjusting the referigerant level so that the evap is producing the correct amount of superheat for the particular referigerant and expansion valve. Superheat is the measure of how much heat is being transferred. The technical details aren't important here.

Your friend had no great insight I'm afraid. The best advise I can give is the same as that given by others here. Put a REAL gauge manifold on the system so you can see both suction and discharge pressures. If the suction side is, indeed, standing at 130psig with the compressor turning -- and the high side isn't off the charts -- then either the compressor valves are leaking badly (which isn't too likely) or there's a pressure relief valve in the compressor that's open.

Buy, beg, borrow or steal a set of gauges before you do anything else.
 
Does anyone know if places rent out real gauges? I completely just bought a $19.99 hose gauge from AutoZone. :frown: Havent used it yet, but they did have a Manifold Gauge for I believe $39.99 in there... would that be worth anything?
 
if you buy an A/C manifold and gauge set, be sure it has the QD connectors for 134. Those are not that easy to get separately and are expensive.
HF has a set for car systems that they have regularly on sale for about $40 with the QDs. Don't know how accurate.
Not all inexpensive gauges are bad, though. I have a pro Yellow Jacket manifold type set and it was pretty close to what my cheapo Kragen filler / gauge set was indicating.
 
I am a 40 year+ auto mechanic and I have run into this problem only twice in my time as a mechanic.

I have found that every once in a while the reed valve will have some of the fingers break off and the freon pressure will back up on the low side of the system.

This is more common on vehicles with an expansion block moreso than one with an orifice tube.
 
You must log in or register to reply here.

Share this page

Back
Top Bottom