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Weak AC at Idle

My 2005 Subaru Outback 2.5XT’s AC is weak at idle. It is better at highway speeds but never as good as my wife’s 2005 Toyota Camry. I had the system evacuated and recharged (with dye) by the dealer. The mechanic let it sit overnight and found no leak. He said the evaporator is the only part of the system that he could not see and, therefore, it might have a slow leak. He said I could replace the evaporator or I could wait until it gets worse. He said the system is generating good pressure 250/28 psi. The cooling fan behind the condenser runs while the car is at idle. Question: What should I do? Should I replace the evaporator? Will this fix it? Is there any other testing that can be done before replacing the evaporator?

After the mechanic recharged the system did it cool properly for a while?

No. I just left the mechanic today. Barely cool at idle, and 75% as cool as my wife’s Camry (while idling) at 60 mph.

First get a small thermometer and measure the outlet air temp. Let us know the temp and the humidity for the day you measured and I will look on the chart and see if you are in spec.

When they switched to R-134a, A/C performance at idle suffers for most cars. Some makes and models of cars put a little more effort into their A/C systems than others.

28 PSI suction with full weighed in charge, and not very cold air could be a indication of a expansion valve not functioning properly. Find a better shop that specializes in A/C repair, and have them check the expansion valve performance.