Help With Heater on '95 E320?
 

The heater on my e-class started acting erratically and making weird "glass tinkling" and groaning noises. I checked the supplemental pump and it is drawing 960 millivolts, so based on previous posts here by Larry Bible I assume it is ok. However, I noticed that the shorter metal vertical canister in back of this little pump (a servo valve?) was getting extremely hot and I could feel the coolant flow thru the connecting heater hose surging like the a valve was shutting off and going on suddenly and repetedly. I unplugged the connector from this (valve?) unit. Is this a valve? Do they go bad in such a way? Is this my problem and if I replace it will my heater problems be solved, or is there a decent chance that this has also screwed up the electronics behind the dash? Thanks for any help!

The valve regulates the amount of coolant that flows through the heater core in order to regulate the temperature. Either the valve is faulty or it is recieving the incorrect signal. The fact that it keeps shutting off and on would lead me to believe that it is recieving an incorrect signal for some reason, but I do not have a great deal of experience with this. Hopefully someone else here can give you advice on how to further diagnose your problem.