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1985 300SD
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831 Posts
Discussion Starter · #1 ·
I did the citric acid flush this past weekend and installed the new thermostat. I checked the monovalve (recent rebuild) and also checked the aux water pump. All working good. I started the car on the way home from work this morning (25F) and it warmed up quickly. I turned the thumbwheel to max heat and hit economy. I got good heat from all the dash vents. Less than a minute later I hear a click, clunk from inside the dash. Now I get cold air from all the vents. I toggle a few buttons and hit the button for the vents and floor. Now I get lukewarm air from the LEFT CENTER vent only and all others are cold. A few minutes later they are all cold again.
I noticed this yesterday when it was warmer. Of the 2 center vents above the radio only the left one would blow warm air.

Thanks in advance and sorry if this was covered previously.
 

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1991 300 SE
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18,534 Posts
When you refilled the system with coolant, did you turn on the heat with the t stat open and add more coolant if needed? Sounds like the heater core took a big gulp of air.
 

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1985 300SD
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831 Posts
Discussion Starter · #3 ·
I thought about that too. For the entire process of flush and fill I left the heat on full blast.
 
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