I've done a few searches on this one and I thought I was getting close. I just don't have the time to sit down and filter through all those posts. I am watching my 3 year old son and working odd shifts in the meantime.

Anyway, 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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'85 300SD (formerly california emissions)
'08 Chevy Tahoe
'93 Ducati 900 SS
'79 Kawasaki KZ 650
'86 Kawasaki KX 250
'88 Kawasaki KDX200
'71 Hodaka Ace 100
'72 Triumph T100R

bump....it is cold here

__________________
'85 300SD (formerly california emissions)
'08 Chevy Tahoe
'93 Ducati 900 SS
'79 Kawasaki KZ 650
'86 Kawasaki KX 250
'88 Kawasaki KDX200
'71 Hodaka Ace 100
'72 Triumph T100R

What happens if you pull the connector on the monovalve and turn on defrost? You should get full heat, full speed blower behind the windshield.

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'82 300SD - 361K mi - "Blue"

"Good judgement comes from experience. Experience comes from bad judgement."

listen, look, .........and duck.

I can get full heat, full blower at the defrost now without pulling the monovalve plug.

__________________
'85 300SD (formerly california emissions)
'08 Chevy Tahoe
'93 Ducati 900 SS
'79 Kawasaki KZ 650
'86 Kawasaki KX 250
'88 Kawasaki KDX200
'71 Hodaka Ace 100
'72 Triumph T100R

I had a monovalve failure years ago where I wouldn't get heat unless I shut the engine off, put the heat wheel at max and then restarted. It would heat until I moved the heat wheel. Do you get full heat in economy with the monovalve disconnected?

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'82 300SD - 361K mi - "Blue"

"Good judgement comes from experience. Experience comes from bad judgement."

listen, look, .........and duck.

If you hear the clunk in the dash which corresponds to your heat loss, the problem might stem from either the climate control unit itself, or one of the thermostat switches improperly reporting you've reached cabin temperature. The fact that it works fine on defrost more or less eliminates the monovalve and pump, which you've checked anyway. Different models have different thermostats that help control the whole thing. Check the manuals.
Ben

If the temp wheel is at full heat and I hit Econonmy the fan will start slowly and then you will hear it start to gradually blow faster and faster. At this time only lukewarm air will blow from the left center vent. All the other dash vents will blow cold air. If I then hit Defrost button it will switch to blowing at the defrosters and the air will be hot. If I then switch back to full heat (button with solid up/down arrows) I will get cold air from all dash vents.
This is driving me crazy.

__________________
'85 300SD (formerly california emissions)
'08 Chevy Tahoe
'93 Ducati 900 SS
'79 Kawasaki KZ 650
'86 Kawasaki KX 250
'88 Kawasaki KDX200
'71 Hodaka Ace 100
'72 Triumph T100R