560 SL 1989

Heater does not come on. Blower works fine, (only cool air). If I turn off the engine and restart it, I get heat for about 1 minute. Position of tempurature wheel makes no difference. Turning it all the
way up does not cause heat to come on. Any ideas? Bad sensor somewhere?
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More likely bad heater selenoid valve that controls the flow of hot coolant to heater core.
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Replace the mono valve insert. In the heater water valve on the firewall, passenger side.

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Yes, it was the mono valve. I did not see any tears or wear in the old one. It looked brand new. Replaced it anyhow. Nice and warm now. Funny thing, the metal sleeve that you put back in last (after the washers) had some notches cut out of the top edge like it was supposed to mate with something. I saw nothing that seemed to line up with the notches, but it is not leaking so I guess that is not important? John
Karl wrote:

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