I have a 99 SL with the dumbest climate control system I've ever seen. When I drive the car for 45 minutes or longer in either hot or cold outside temperatures all the vents close and no air comes out to heat/cool the inside of the car. I can hear the fan blowing and the system is smart enough to know to ratchet the fan higher, or I can manually increase the fan speed but to no avail for the vents are closed. Changing the air to defrost or floor also does no good. The only way to snap it out of this is to either shut off the car and restart or turn on the "EC" button, wait exactly 30 seconds and the vents open.

I've had the car to the dealer under warranty 8 times over the past 14 months. They have replaced the inside temp. sensor, blower motor, blower motor regulator, the climate control push button assembly (twice), the A/C Vacuum block, and for some reason the keyswitch. They tell me what I'm experiencing is "mechanically impossible", yet it happens almost every day.

Is something broken or is the 99 SL's climate control just really stupid?

 

if there's a signal that the top is down, the A/C got very limited function.

they might be looking at the wrong direction?

 

it may be the evaporator temp sensor if it reads wrong the ac evaporator freezes not allowing air to blow through it. check this by lifting the bonnet and checking the a/c pipes if there all frosted up that will be it

 

The climate controller has built-in diagnostics for retrieving actual values and stored fault codes and showing this information in its display window. If you send me an email I can give you the procedures.

 

I'm keeping an eye on the evaporator temp. sensor values on the diagnostics panel. It's showing values in the mid to upper 60's, which I'm guessing is normal. The problem happens intermittently so I'm waiting to see what it reads when the problem occurs. It fails more often when it's warm out, and it's been cold lately (as cold as San Diego gets that is).

Thanks to everyone for your help.

 

I have heard of this before; I would love to know the solution to this one