How do I check the climate control servo on w116?
 

I have a 1979 300SD that does not have heat in any mode. Every button works and does as it should though. I hot-wired the water pump that is on the servo, and the pump did spin. Do you guys know what else I need to check to see if it is the servo before I buy a new one. (probably used though).
Thanks
David

I believe if you operate the controls and listen to the servo, you should be able to hear the valve operating.
You probably don't want to buy a new one. Close to $1000. A rebuilt with a metal body is the best bet. Randy at European Parts Specialists had the best price last time I looked. Around $300. Do a search on this forum and his phone # should come up.
I'd shy away from a used one unless it is a metal bodied one. Those things are prone to cracking.

Will the whole unit split and leak coolant? Even if mine is cracked shouldn't it still work or is it something inside that cracks?
The little water pump is not getting electricity when trying to use the heat. When should it get electricity? Would the servo switch on the electricity to it or would the push-button unit do it?
A few weeks ago I pulled out a CD player to look at the CD wires. When I did that, I pulled out the push-button unit because it was party pushed into the dash. Could I have left something unplugged that might have let everything work but the heat? All the functions do work, such as when defrost is on it blows only at side vents and windshield, while at the same time the compressor is turning.
Sometimes when I switch the climate control off it will take maybe 4 or 5 seconds to stop blowing our air. Their was also one time during the summer that it wouldn't shut off. As in that it kept blowing out air at the vents.
Thanks
David

anybody?

It is starting to get very cold here in northern IN. I have NO heat at all.
David

Do a search on the topic and you will find posts describing how you can bypass the servo to get heat if you don't want to replace it.

When you set it to heat does the air from the center duct stop? If it does the servo is being controlled. It is possible to adjust the temp wheel and get the servo to move farther to open the valve. It is likely that its shot if you get this movement and no water flows.

The pump only works below some temp. Try putting power to it and see if you get heat. If you do put a toggle switch on it.