I've had my issues with the climate control on my 280SE. It was working well for a time, but now is not quite right. Maybe the readers of this thread can help.

I replaced servo with George Murphy's aluminum unit, along with the amplifier and aux water pump. After the car sat for some time chasing other issues, I found the AC cold and fans working, but no heat. I checked the fuse that brings the servo back to 'park' position- that now works. As does the aux water pump. I've also tested the servo at pins 3 and 5 straight from the battery- I hear the valves open and close as they should.

Now here is the problem. When I measure voltage at the plug side that feeds pins 3 and 5 into the serov unit (ignition on, ACC set to 'DEF') I only get 8 or so volts.

I believe this is not enough to drive the servo, so of course no heat. What could be causing this? A bad amplifier? What feeds these pins- connections from the amplifier or a direct switch from the selector switch on the dash?

jk