jmartin0113

I have a 2006 CLK 500 hardtop coupe. I live in Texas. At first, when the AC was on medium fan speed blowing from the normal dash vents, it would suddenly slow down, then speed up, and then start blowing super fast from the DEFROST vents and the AC would change to HEAT. I'm not talking normal outside Texas temps, I mean HEAT. This would sometimes happen right after turning the car on or 10 miles into a trip. Sometimes the "Off" button & fan speed would respond, but mostly they wouldn't. The blower even continued sometimes after the AC was off and the key was out. Later on (hours or days later) the AC would work perfectly fine for days at a time. I drive 30 miles to and from work.


Then, about 5-10 days later, the AC started doing something different. When starting the car or in the middle of a trip, the AC fan would slow down, pick up speed, and then start blowing somewhere under the dash. The dash speaker cover was cold to the touch, but not much coming out anywhere else. And, sometimes it would still blow HEAT from the defrost vents.


So, I did the "Reset" of holding down the defrost & recirculate buttons. They cycled fine and the lights quit flashing. It seems the AC would be okay for a little while after that. I did this any time the AC started acting strange. "Little while" meaning 10 mins to 48 hours.


Now, there is NO FAN at all. When I do the "Reset", the lights keep flashing.


We did remove the AC control panel. Everything looked okay in the back, no obvious issues.


AC filters under the dash are CLEAN.


Coolant is GOOD. We checked it twice. When the AC works right, it is COLD.


Compressor IS RUNNING.


I am mechanically inclined & plan to do any necessary work myself, if I can.


I am open to any ideas y'all might have. Thanks in advance!

Rudeney

I suspect the ACC itslef (the control panel) is failing. You really need to get codes pulled from it to know for sure, and that requires a specialized tool like the dealer's SDS (Star Disgnosis) or iCarsoft i980/MB-II. Generic OBDII scanner won't do it.

JimVonBaden

Mine did the same thing. It was frustrating. I pulled the control panel and cleaned it with electrical cleaner. It worked for a week, then bad again. I replaced it with an E-bay one and so far so good.

jmartin0113

Thanks for the help. We did replace the main AC control unit, but that wasn't the issue. The issue was the sun sensor in the front below the windshield. It had corroded and I guess might have been shorting something out. We just removed it completely. So, I have COLD AC and life is GOOD in South Texas!

Rudeney

Dang! I'd never have figured that would cause no AC - maybe AC when you didn't want it, but not shutting it off.