Similar problem with my mom's a/c in her corrolla. After car is warmed up passenger side got warm and the furthest left vent (driver side) would be cool. Had can of refigerant with gauge and decided to check coolant level and it showed low. I refilled to optimal level and has been normal for 3 months now. I assume there is a coolant leak.

Thanks, I appreciate the input.

I had the exact same problem. The vents would all start out cool. Then slowly the passenger side vent to the driver side vent would get warm. But the vent next to the drivers side door would be cool. Not cold, but cool. My issue was caused by a failing compressor though. It could just be low refrigerant as well.

I recently had the compressor bearing go out, and after replacing the compressor. The warming issue started. When the compressor bearing failed, there was some debris that made it into the lines. The debris got stuck in the evaporator (the radiator inside your dash) or the expansion valve on the evaporator. This was causing an issue with the pressure inside the evaporator, making it get warm. I had to replace the evaporator, dryer, and the compressor again. Blew all the lines out, to insure all the lines were free of debris. Vacuumed the system down, refilled, and it was good. Hope this helps.

Thanks, I thought I was going crazy because of the temperature difference from the right to the left. I put a can of refrigerant in yesterday and it was cold all day today. I feel there is more to it though, the compressor doesn't seem to be cycling on and off like it used to. I am going to keep trying to figure it out, the leaked refrigerant had to go somewhere, and I could find no visible leaks in the engine bay. I really hope it is not the evaporator core. Thanks again.

Seeing a leak is usually slim to never seen, unless it is a larger hole. They make a florescent dye, Tracerline, that can be added to the system. It "highlights" the problem area for slow leak systems.

There is also a product, Super Seal, that is added to the system that plugs holes from the inside. This is a cheap quick fix, but I don't recommend it. It reacts when it contacts air, and hardens. I have heard some SERIOUS horror stories with people using it, and also some great things as well.