98 E320, heater only works in defrost or HI after new waterpump

Group, See if any of you could 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, who recently Aquired my services after
another Foreign car specialist miss diagnosed a weird high rev engine noise. The waterpump bearing was gone and caused an unbalanced vibration, the other shop didn't even missed this but 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 poor heat. He came back a day later, I found that there was no heat,unless 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 was getting a pulse while 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?. Martin. Autobahn Auto
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Martin,
You drained some of the coolant to change the WP.
Could the heater be air bound?
My 2 cent contribution.
Tom
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Motorsforum.com is a website by car enthusiasts for car enthusiasts. It is not affiliated with any of the car or spare part manufacturers or car dealers discussed here. All logos and trade names are the property of their respective owners.