If I'm doing city driving and stop and go it goes warm
Ac System has full 134a pressure
And the pump stays engaged even when it stops being cold
Any ideas?

Forgot to mention this is a 2001 E320

Pretty vague description without ambient temp, duct temp and pressures. But your saying its OK going down the high way, no mater how long you are going down the highway.

__________________
To see my 129 parts for sale visit:
http://stores.ebay.com/The-Mercedes-SL-Store
John Roncallo

Sounds like the fan isn't working. Start up, condenser hasn't really heated up yet, but once there it seems like the heat isn't being dissipated during stop and go traffic, unless you are moving to get air through the condenser. Also, could be that the compressor isn't properly compressing unless the rpm's are higher causing it to spin faster....unless it's a variable speed or you are low of refrigerant. In any case, the electrical is easy to rule out, either the fan is working or it's not. Then you'd just need to check the refrigerant in the system, and next move on to the mechanical. Since you have some cooling, it shouldn't be too hard to figure out.

__________________

1990 190E 3.0L

New to the forum and this question may have been asked previously but after searching I finally gave up and decided to ask. I own a 2011 C-350 (W204) with an A/C problem, I'm hoping somebody has run across the same problem and had a simple fix. The AC blows cold air sometimes and for no reason starts blows ambient temperature air. Could it be the Evaporator Temperature Sensor (Switch). Or does anyone have any additional information that would help me solve my problem. The local dealer said they thought is was the AC modem (the brain that talked to the AC system) and quoted a price of around 3,000k and didn't guarantee that would fix my problem. Everything works perfect when it works so cold you have to turn it down. Any suggestions or help would be greatly appreciated.

Thanks
Bill