My AC is driving me nuts. Blows warm at idle, blows cool at driving speeds, but not cold. New Compressor, accumulator, orifice, and evaporator 3 years ago,worked great til last month. Static Pressure is 150 psi (ac off), ac on at idle (90 degree outside air) low side 100 psi, high side 200 psi. Pulled and replaced orifice tube with no change to results. Thinking compressor is going. Any thoughts or help greatly appreciated.

 

Low side is way high. High side looks good. When you changed the orifice tube you had to open the system... Did you pull a vacuum before charging? If you didnt, you most likely have air in the system.

In some cases it could be that you have a high charge or air in the system... Could also be compressor but I wouldnt use that one first...

 

I pulled vac for 1 hour before charging.

 

Were you able to get an accurate measure of refrigerant in the system? Could be high charge. Otherwise it could very well be compressor.

 

Added 3 12 oz. cans, factory charge is 33 oz.

 

Yeah that would not be enough over to cause problems.

 

Clogged condenser fins causing high pressures possibly?

 

Usually when the condenser is blocked the high pressure side also goes way up... The condenser is on the high side.

 

it sounds to me like the compressor is starting to fail, and bypassing from high side to low side.

 

your compressor valves are fine, if the compressor valves were bad you would have a low discharge pressure witha high suction pressure. You have one of 2 problems ir a combination of both of them.
Air and non condensible gases or an over charge. Both will cause high suction and high discharge pressures at the same time. For R-134a your suction pressure should should be between 25-35 psi. Your discharge pressure will vary because it is an air cooled system. 200 psi is on the high side for an R134a system.
For discharge pressure take ambiant temp plus 20 degrees(for a newer system with clean condenser) and ambiant temp plus 30 degrees (for a dirty system) and cross thet over on a PTR chart to get your discharge pressure.(Refrigerant Pressure and Temperature Chart For R-22, R-410A, R-407C, R-134A, R-404A) If your condenser is dirty then it really needs to be cleaned or replaced.
Your static pressure is high, also indicating air and non condensable gases or an over charge. 150psi static crosses over to about 111 dgerees ambiant temp. To get an accurate static pressure let the truck sit over night so the engine compartment is cool and double check the pressure and convert that directly to temperature, it should match, for example 75 degree outside temp you should have 78 psi charge.

How long did you hold the vacuum for to check for leaks? If you are sure you pulled adequate vacuum and there are noo leaks allowing air in the system then you have an over charge.

Me personally i would recover the refrigerant, pull another vacuum and recharge.

Matt

 

Thanks Matt for the info. Tested again this morning on a cold truck and here are the results. 80* ambient temp, 80 psi static, 60 psi low side at idle, 115 psi high side. According to the chart from the link, 80* ambient should yield 86.7 psi. Think I will evac, pull vac and see if it holds.

 

While you are pulling the vacuum on again get some good cleaner/degreaser and soak the condenser then hose it down to get it clean. Good luck with it. If you have any questions let me know

matt

 

Excellent information in this thread!

 

As others have stated great info, but I take those universal charts with a grain of salt. Always consult the manufacturer's specifications before taking those values as gospel.

I agree in this case the OP has something else going on. What was used to pull the vacuum, did the vacuum hold, etc.? One thing that will kill A/C performance is the oil charge. Too much is as bad as too little. I am not certain what it will do for pressures, but vent temperatures will suffer accordingly in my experience.

 

Well been doing this in industrial settings for about 25 years and PTR charts have always been accurate.

The OP needs to make sure it holds vacuum for at least 30 minutes before charging. If there is any appreciable loss of vacuum then he needs to find the leak.

matt