I have an '08 Pathfinder SE with about 150K miles on it. Lately the AC does not cool much at all at low revs. At high revs it seems to work much better. Driving in stop and go traffic around town, the AC can't keep up with the summer heat. Get it on the highway and the AC works pretty well.

I took the truck and had the AC serviced. They said it was low and recharged it. However, they say it still doesn't cool properly. They are charging me $125 for the AC service and another $135 to further diagnose the issue.

Any ideas what could be the problem?

Thanks.

The compressor pump may be worn out, no longer able to reach or maintain high pressure. If the A/C clutch is constantly engaged and never disengages while the system is running or it disengages only for a few seconds intermittently, chances are your pump cannot compress enough gas to reach the high pressure limit shut off or it reaches the shut off limit but cannot maintain the high pressure as long as it should. Higher engine revs will make a worn out compressor seem like its working better than at low engine revs when the worn out compressor can't keep up with the pressure loses while the A/C system is running.

That being said, your '08 Pathfinder has a more complicated system than older vehicles. There is a self diagnostic feature of your A/C system that will put your A/C operation into a fail-safe mode when certain components and sensors are detected as faulty. This will limit the normal functioning of the system until the fault is corrected. Nissan service center's Consult diagnostic system is the only way I am aware of to determine what the onboard computer of your vehicle has flagged as a fault. It's might be best to let a Nissan service center or an authorized service provider, with a Consult diagnostic test system, figure out what has gone wrong. The problem might turn out to be a simple, relatively inexpensive, repair compared to replacing the compressor which may or may not resolve your issue.