I have just noticed during my recent trip that my A/C is very cold at freeway speeds. It wasn't very good at cooling the car in normal city driving.
During a long toll stop I noticed the A/C was getting warm and my temp gauge shot-up closer to 120C. I of course turned off the A/C and cranked the heat (arrrgggh 90F out) and waited until I could get back to highway speeds. Which, of course, returned the temp to normal when I was at freeway speeds. I'm thinking maybe the aux fan switch is dead? To answer the A/C @ idle vs highway speed though, compressor going bad?

 

it's the cooling on condenser. not enough ventilation or aux fan not in good function.

 

I have this taking place on my 95 E420. it is definitely more cool when moving than idle. However, all of my fans are functioning? It also appears to be more of a startup difference. Once it is blowing cold, it will maintain cold at slow and idle traffic. However, to startup at work and immediately go out into slow or idle traffic can be miserable at times.

 

could you try crimping the hose on the hot water valve and test?

leaky duo valves cause this problem too.

 

I am going to pull out my CD manual and see if I can find this. I also read that the recurculation should come on above a certain temp. I have tried manually hitting this switch and the light does come on, but I do not notice a difference when it is on. In my other cars when I turn off outside air, there is a pronouced difference...in my chevy truck I actually hear it close up. I am questioning if this is occuring also..........this may be what you are referring to?

 

OK, finally had a chance to test the operation of the aux fan. It's dead froze in one direction, but works (albeit loudly) in the other when i jump the terminals and reverse them. Can this fan be dissassembled and dealt with?

I was tempted to leave the terminals reversed but it's too dern loud!! [sm=badidea.gif]