Date registered: Sep 2004
Vehicle: 2014 E250 Bluetec 4-Matic, 1983 240D 4-Speed
Mentioned: 3 Post(s)
Quoted: 256 Post(s)
RE: E320 1999 W210 Air cooling differences
I have a similar problem. My driver's side vents will arbitrarily decide to go from cool air to hot air by themselves. I have to run the system in defrost mode for a few minutes and then the system clears and operates normally.
By the way, I think the "hissing" sound you hear is pretty normal. There is a valve that controls the flow of the refrigerant through the evaporator. When this valve cycles on you hear the noise because the liquid passing through the valve boils on the low pressure side.
If you have managed to fix your problem, please post the fix so we can all see what this is. Very odd, the passenger side is not affected. Jim