Ac Freon Too High

JsHwrdul · June 1, 2011

I recently purchased a 2002 Yukon Denali, and am new to this board. I have just recently started using the AC on the car and noticed that at idle the AC doesn't blow very cold. So I checked the AC pressure with a gauge I picked up from autozone and it was sitting between 80-100 PSI. Obviously this is much too high (or seems to be from every other vehicle I have owned/serviced before.) Did the previous owner fill the system too much, or is there something else going on here. Any information is greatly appreciated.

tyhuck · June 1, 2011

If the system is over charged, it will cause the dryer canister to form ice on the outside.

From what it sounds like, your compressor may be on the way out.

Not sure what to tell you about the guage readings, but you never can tell about those cheap gauge sets. Ide check it again with a professional grade set of gauges.

AirForceAngler · June 1, 2011

Are you checking the high or the low side? If that is the pressure on the high side, that's probably too low. It takes more than one guage to determine the proper service of the A/C system and it is also dependent on the outside air temp.

Doug_Scott · June 1, 2011

Assuming the a/c was off or the engine not running, normal pressure at 80 degrees F will be about 88psi for R-134a. If the engine was running and the a/c running, the high side pressure should be 2.5 times the ambient temp, with the low side being about 30psi. There is a lot more to a/c than just the pressures though, and how you interpret the pressures is not just simple logic.

oldmann · June 1, 2011

Make sure you take a suction side reading with the AC comp actually working. Put it on as cold as it will go and on high to make sure. Ariound 100 should be good. Then see how high the pressure is. Is it turning on and off rapidly? If so, it is too low.

Doug_Scott · June 1, 2011

Make sure you take a suction side reading with the AC comp actually working. Put it on as cold as it will go and on high to make sure. Ariound 100 should be good. Then see how high the pressure is. Is it turning on and off rapidly? If so, it is too low.

If I am reading this correctly, you think 100psi is a good reading on the low side (suction side)? Unless they have changed the a/c systems completely recently I don't think 100psi is a good reading for either low or high side (unless it is about 45 degrees outside and you are measuring the high side). I may be wrong here, the last I worked on a/c was in the R-12 days, but I can't see how it would be that different with R-134a.

Spurshot · June 1, 2011

I buy my components and tools from these guys. I've spoken to them on the phone to troubleshoot as well as within their forum. If you're gonna learn a/c diagnosis and repair, I recommend you get on their forum and learn before you get too deep.

This is a link to their site with a pressure chart and it has a link to their forum.

http://www.ackits.com/aacf/ptchart.cfm

the pressures are when the engine is running with a high idle (1500 rpm -ish). Static pressures are not how a system is checked as the low and high will equalize when not running the compressor.

When filling with freon, generally, the clutch circuit is jumped to continuously run the compressor. Pressures are checked when the compressor engages during normal operation as pressures will go up and down as the compressor engages and disengages.

Freon is recommended to be added by weight by GM. Then pressures should be checked and freon added as needed to get pressures right. Caution should be used in adding above the specified weight requirement as you can "hydraulic" the compressor. I'd limit adding above the spec weight to no more than about half a can.

pm26 · June 1, 2011

As correctly stated, proper pressures are only a part of the equation as far as proper A/C system operation goes. I have seen problems where the pressure were good, but the system performed poorly, It turned out that there was a serious blockage in the orifice tube ahead of the evaporator. There are basically two types of automotive A/C systems. One uses an expansion valve and receiver/dryer, the other uses a fixed orifice tube and accumulator tank. The expansion valve or orifice tube can get clogged easily with sediment and debris, especially if the A/C compressor fails internally and the system is not flushed.