I just purchased an slk 230 98' I checked the air cond today, and found that the drivers side blows cold air but the passenger is hot air. I have both dials on cold setting. How do I fix this? thank you for your help

 

Is the air on the passenger side really hot like it's coming from the heater? If so, then it's probably the heater control valve (also called the dual-valve). It's an electrical servo-controlled valve in the engine compartment and it controls flow of coolant through the heater core. The driver's side and passenger side are indepenent and the passenger side is probably stuck on. This happened to me when I pressure-washed the engine bay. The pressure wash forced water inside the electic component of the valve and shorted it out.

 

Thank you for your help. I am not sure where sensor is located. Do you know where I can get a picture or diagram? thank you.

 

I figured it out, they are two little cylinders on the passenger side. I took them apart and cleaned the contacts ect. now it seems to work. Thanks for your help!

 

On my 2000 SLK230,when the motor is at 180C (normal operating temperature) and when I turn on the heater to maximum heat (red zone), maximum blower speed (5) for the driver and passenger sides, plus vents on the floor and dash are wide open and it is 32 F outside (night) I feel cold air coming out from all vents. If, however, I speed the engine up to 3,000 RPM's the air quickly gets hot from the vents and floor. When the engine returns to an RPM at or below 1200 RPMs for a few moments, the hot air slowly return to cold again. To stay warm, I have drive around in lower gears to keep the RPM's above 2,400 to heat the cabin and keep it warm. What is causing this? What must I do to fix this? I purchased an OEM dual electric regulator which regulates the passenger and driver side of the cab for heat control. I have not installed it yet. I took the current regulator apart and found no corruption in it and the valves worked up and down with gentle touch easily as they should. I replaced and checked the radiator, coolant and heater hoses. No bulges, lumps or leaks. I put on a new water pump... works fine for engine temperature regulation. I flushed the entire cooling system installed the correct coolant mixed 50.50 with distilled water for the SLK 230 (per specs). I replaced all of the hoses that deal with water deliver including the heater core hose. I purged air from all hoses by squeezing them b into a water container to see the bubbles of air purged form them (thus eliminating air bubbles in the cooling system). I bought a new radiator cap. I installed new pully belts. I replaced the cabin air filter. I checked the control cables on the dash were working properly (they are). Radiator fluid is filled to between the full and add marks on the overflow tank. I then I prayed! Still has the same problem. I have concluded that I have to back flush the heater core and install the new regulator. If that doesn't work... any other ideas? Please advise.

 

Wow, getting this notification was a blast from the past since I traded in my SLK230 in 2001.

When you "flushed the entire cooling system" how did you do it? Your vehicle is 20 years old and my best guess is that you've got a blockage somewhere and it probably needs to be removed by dissolving it with a chemical flush. I'm not sure what they use now, but I'm pretty sure MB used to recommend adding powdered citric acid to the coolant for a chemical flush.

 

Usually when you have to rev the engine to get hot air out of the heater it means you do not have enough coolant in the system or you have air trapped.

Remove the radiator cap when the engine cools down, then run the car with the cap off, if you can park on an incline with the radiator on the high side.

It should burp the air out if there is any air trapped.