This is very frustrating during the summer! The A/C will sometimes work and blow ice cold and then sometimes it only blows hot. I have taken it to the dealer twice and both times it of course worked fine while they had it. But like today it blew warm for 3 hours and then all of a sudden ice cold again. The dealer says everything checks out and they have no idea what could do that. Anybody have any ideas?

Thanks,

Mike

 

good luck on this issue.......btw be sure the the "EC" button on the climate control isn't selected

 

Hi Reddots,

This is going to sound dumb, and it may not be the problem, but I had a similar problem which was the result of my own dumbness.

This summer temps here have been near and over 100F, with 80-90% humidity. I had my ac set on 80, which feels great when its 100 outside.

Cold air would blow from the vents, but in the morning hot air was coming from the vents. I finally realized that hot air was blowing because the outside temp(75) was lower than the temp setting on my ac control (80). So it was actually trying to heat the car to 80.

I hope its somthing simple like that, and not a compressor or valve problem.

Sorry not much help.

Charles

 

Blue Silver, thanks for the reply. I wish it was that simple. One day it can be 100 degrees and you can set the system for 70 degrees on automatic and it cools like a champ. The next day same thing and it blows nothing but hot air. There is no consistancy at all. Dealer replaced temperature sensor but that had no effect. Both times I've taken to dealer it worked while they had it. My wife wants me to sell the car (2002 CLK-430 Convertible) which was her dream car because she's so frustrated with it. She said she'd take a Ford Focus as ling as the AC blows cold! I might be able to save some money out of this deal! Any other ideas would be greatly appreciated!

 

its been a while since ive messed around with a/c stuff...

i believe mercedes use an h-block setup to cause the pressure drop in the refrigerant needed to cool. if i remember correctly, there is a valve that limits the amount of refrigerant flow, which is what will allow different pressure drops based on temperature. if the valve seizes sometimes, be it from moisture, or even freezing, then it wouldnt allow the needed pressure drop which in turn could cause the thing to blow hot air. i dont know if youre familiar with a basic a/c system, but you could feel each line to tell if the base system is working.

line coming out of the compressor and into the condensor should be hot to touch
the line coming out of the condensor and going into the h-block (should be near the bulkhead?) should be warm
on h-block systems there is no line going from it to the evaporator, they are pretty much one assembly...so the line coming out of the evaporator and going into the compressor should be cool to the touch.

if you dont have time to mess around like this, i would say to take it to a dealer, tell them to hook up a box where you can take the vehicle home, and whenever it blows the hot air, you hit a button and it will record whats going on in the car at the time...then you can take it back to them and have the review it. i know it sounds peculiar, but the computer actually sees a lot of whats going on in the a/c system...so it could point them in the right direction.