I have a 95 C280, the air conditioning was blowing ice cold yesterday, today the heater is blowing even with the A/C on. I dont think it's the Duovalve because all 4 front vents blow hot. The A/C is fully charged! Does anyone know what it could be?

Many thanks in advance.

check and see if the EC button is on, if it is this will turn the compressor off

Mossimo,

When I had my AC re-done two years ago (on my '90 300E), I would experience "cutting off" of AC upon acceleration onto interstate. On occasion, after driving for a couple of miles, AC would kick back in; other times, it would not start cooling again until after stopping and re-starting car. Problem turned out to be that fan belt was loose & fan belt was loose because belt tensioner was shot. When I finally replaced tensioner, problem solved.

Check to see if fan belt tight; if you cannot tighten it as it should be, it is likely your tensioner is gone. There is some pretty good info re. tensioner replacement on this site - search belt tensioner.

It's your duovalve ,which defaults to fully open when it loses electrical power. Check your fuses and the connection at the duovalve plug.
Geo.

If it were the DuoValve, wouldn't it have 2 cold vents and 2 warm vents, All my vents blow hot hot air. I felt the AC line going into the firewall and it is very cold. I know the system is ok.

Thanks for your assistance.