See if you give me a hand with this one, I got a clue myself but I like to hear
it from someone else.
I have a customer with a 1998 W210 E320, he recently stopped going to the
dealer because a weird engine noise was mis diagnosed, the waterpump bearing
was gone and caused a unbalanced vibration, the dealer did find this and
changed the boot that seals the steering column to the chassis.
Anyway I grabed the fan blade and found 2 inches of play back and forth.
I changed the waterpump last week, problem went away, but the customer called
back complaining about no heat.
He came back a day later, I found the same no heat, but if you select "HI" or
"defrost" the heat works fine, so I checked for a unwanted pulse at the mono
valve, sure enough, there is a voltage signal when there shouldn't be one, and
off course you unplug the monovale and heat workes great.
I did at first think that the problem could have been a thermostat that just so
happened to go bad after the waterpump change, so I replaced it before I knew
the monovalve getting a pulse whilke heat is aquired.
Question, I think the push button assemply has gone bad, but it is a bit of a
coincidence that this happened right after I changed the waterpump, I mean the
customer said he never did have heat after he picked up his car.
Any other clues, something stupid I'm missing here?.