a/c---Heater
 

I have problem with my temp. wheel, on the control unit, the heat starts when it should be a/c and it goes kinda back and forth--- please help. Thanks, Dennis :confused: P. S. My car is a 1979 450 SL Mercedes.

A few tests...
 

This could be a problem with your servo, the servo amplifier, or the sensor chain. This is an easy problem to troubleshoot. Do you have a voltmeter that can measure resistance? A DVM? If you don't you can get on from Radio Shack for $40 or so.

If your thumbwheel is bad that would be very easy and cheap to fix. We have a rebuild kit on our website for $40.

If the thumbwheel and sensor chain are OK then it's a problem with the servo or the servo amplifier. If either one are bad you'll probably have to replace both or better yet dump the servo and go with the upgrade.

i have up grade servo,so guess i need to trouble shoot a little, Thanks for the reply, Dennis

Not so fast...
 

It's very common for an intermittent open circuit to cause this kind of symptom. If you can get your hands on a voltmeter you might save $500 or so. Here's one for $3!

http://www.harborfreight.com/cpi/ctaf/displayitem.taf?Itemnumber=90899

Thanks alot,but i have one ,i will chack it out--Dennis