Thread: Any A/C experts out there?

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Those pressures are ok, depending on what your ambient is and engine rpm. I don't know if you did it but a person should always spin the compressor over by hand MANY rev's once the system is assembled.

The noises that you describe can be due to unstable/loose mounting and/or loose drive belt. Check this first and then check your pressures again with engine at 2000-2500 rpm, high fan, max a/c, and the condensor fan running. Also, let us know the ambient air temp where the car is.

Stu Cool,

I agree with DennyW. Your high side is too high. I would make sure the system is not overcharged. I am no expert but I am fortunate to be friends with one. I also own a telecommunications company and one of our clients in Dallas is the Sanden manufacturing plant located in Wylie. So I am lucky to be able to ask some of the engineers about the 508 unit in my sedan.

And like the issues you are describing, I too am having similar issues which occured just after I put my engine back together and had the system recharged.

When I called one of my buddies, he told me it sounded like overcharging was the culprit. He stated one of the most common mistakes with aftermarket systems is overcharging. He continued to say that overcharging is usually caused by filling the system by watching the gauges instead of simply filling by the correct measured amount of freon. For example, my Vintage Air system only takes 1.8 pounds of 134a refrigerant. He said any more than that will cause the low/high pressures to be high. He stated the low side should be around 6-12. This may seem extremely low, but he said these systems are very different than stock systems and run a much smaller low side pressure. And the high side should be no more than 2*ambient temp + 20%. So in texas with the current temp around 100, the high side should be no more than 220. Make sense?

When I had the system charged by the local shop (I know...I know what your thinking...but I was in a hurry to make a rod run and took the easy way out instead of doing it myself...another lesson learned!), I noticed a loud "screeching" sound when the engine was revved up. This turned out to be the high pressure switch cutting off the compressor and then allowing it to cycle back on as soon as the pressure lowered. This continued to happen until we drained the system of refrigerant.

It now works, but not as well as it did before when it was charged correctly. So this weekend I plan to vacuum the system down and start over. This time I will charge only the correct amount and I expect the problems to be solved.

Again, I am no expert, but I trust my friend and he knows his stuff! I will let you know how it turns out.

Denny's right on the money, I would suspect it's a stuck expansion valve, It does concern me that you said you did not add oil as most compressors are shipped with out oil in them. Your low side is positiveley too low, but the high side doesn't seem outa reason as with R134a with temps in the 90's I usually see about 40 on the low side and around 250 on the high side as an average at idle speed. rule of thumb on the oil is 2oz for evap. 2 oz for condensor,1 oz for hoses, and then the compressor will need whatever the compressor manufaturer calls for. Either way I would first put a new expansion valve on it, I say expansion valve instead of orfice tube because all of those units I've seen use an xvalve....

troy-cryer makes a lot of sense also,maybe try letting some gas out of it and see what happens,because if it's putting out 38 degrees at the vents there can't be a hole lot wrong as most oem stuff I work on will only put out about 45-55 degrees at the vents.....

Not a auto ac tech, but the metering device sounds like the problem. High head usually gives you high back pressure. A restriction will drop your low side pressure and the more refrigerant you add the lower it will go, hence slugging the compressor with liquid, not good. Is the suctions line sweating?
Is the metering device rated for 134A? 36 to 38 degrees to cold, kinda also sounds like improper size condensor. Wish I could help more, just thought I add my 2 cents. Stu Cool.