sb001

Driving home this afternoon in my 99 Maxima, actual temp outside was around 92-93 degrees. My car has had an issue ever since I got the AC fixed a couple months back where it just doesn't blow as cold air as it used to, even set on lowest setting (65 degrees) unless I am driving continuously... in stop and go traffic it blows cool but not cold. So when i got home I put the auto climate control system in diagnostic mode to check and see if the "trimmed" temperature setting had been moved up any when the AC was worked on. The trim setting for temp was set to 0 so that was OK-- HOWEVER, when i ran the diagnostic the ambient temp sensor read 112 degrees, and the in-car temp sensor read 107!! I can understand the sensors being a little bit off from actual temp, but 15 degrees?? What is wrong?? Is this somehow related to (or could this be affecting) the AC blowing cool but not cold air in stop and go traffic (which I was in?) Or am I looking at a multitude of problems?

The Wizard

iTrader: (43)

I don't see the nexus between your AC not being cold enough and the ambient/inside temperature readings. Totally two different issues. Try topping off your AC to see if you can get your AC to blow any colder.
Also, put a temperature thermometer inside your center AC vent and report back the temperature. Have your fan speed set to low or medium at the most when doing this. Rev the engine to 2500 rpm as well.

The outside temp sensor is in a bad location, and probably gets heat soaked pretty quickly, thus throwing off the readings. When you're cruising down the highway and the sensor is receiving cool air, what does the outside temp display when you hit the AMB button? Is it close to real life temps?

sb001

Well TBH I don't really check the ambient temp that often, but from what I can recall, the ambient temp reading was always fairly accurate both cruising and in stop and go traffic until today (now I was backed up in EXTREME stop and go traffic due to an accident, so maybe it has to be that bad for the ambient temp to get thrown off.) Still I do not deem a 15-degree inaccuracy acceptable under ANY circumstance. And it wasn't just the ambient temp- the in-car temp was also way off ( no way it was 107 degrees in my car even with the AC not blowing as cold air as it used to!) Yet the diagnostic mode showed nothing wrong with either of those sensors, so what's up??
As for the AC not blowing cold enough, when you say "top off the AC" I assume you mean the refrigerant, but that is something I am not inclined to mess with as to do it properly requires vacuum pumps, gauges etc. It's not as simple as just opening a cap and blowing refrigerant in. Any anyway I had the AC professionally repaired by an ASE mechanic so I have no problem taking it back to him. Since you recommended placing a thermostat in the CENTER vent, I'll also mention that the center vent does not seem to blow as strongly as before either. Hmm.

The Wizard

iTrader: (43)

Topping off the ac is actually quit easy, I've done it several times. See link.

DennisMik

iTrader: (2)

Checking the charge of the compressor is a good idea. Thinking about the sensors, perhaps the air tube between the air grill in the dash and the sensor itself on the duct work is plugged. Relatively easy enough to check.