1999 B2500 w/ 5.2 L 318 Front + Rear AC
I have noticed the AC cooling is about ten degrees hotter when sitting still in traffic. Cools fine once I get moving . I also noticed that when still, the engine temp raised up to around 195 -- I replaced with a 180 thermostat and it normally stays around 180. The outside temp was around 90.

Could I have abad viscous clutch fan? I don't see any problems listed in archives. Iusually clean the condenserfins once/year and I will do that next.

Thanks,
Lee

 

That's typical behavior, there's nothing wrong. The reason it's not as cool when sitting is that the compressor is not spinning at as high an rpm as when you're driving. At idle you're spinning at only 700 or so rpm and 1500+ while driving. It stands to reason that you will get more cooling power out of the system as you're driving along.

Radiator fan: With the engine OFF spin the fan by hand. If there is resistance it's good, if it spins freely is needs to be replaced. Bear in mind that on a 90 degree day any engine will run hotter than normal, unless your cooling system is in tip top shape (ex. brand new radiator).This is especially true when sitting still due to the lack of air flow that a moving vehicles gets.