We have a 2.5S Altima, 2002 model. The heater does fine at highway speed. Around town, it blows much cooler air unless you rev up the engine, and then you can feel the air getting warmer. Could this be caused by air trapped within the cooling system? It started last year after radiator service, and I would like to fix it before January cold arrives. Any suggestions?

 

Yes that could very well be your problem....make sure your coolant is full to ... have had quite a few altimas come in with the same problem and it was just their coolant being low.