This is my first post..But I'll try to be clear.

My 82 300 CD Turbo has been cooling just fine all summer here in Arizona.

However, now winter is here , yes even here in AZ. I set the heater for hot

air & it works just fine for about a half hr, goes to 120 Deg. I turn the

roller down a bit & the air goes full cold. I have reset the roller to hot a

couple of times & the warm air returns, but goes cold again.

The question of course is...Where's the fault? Control, Monovalve,?

Sensor,?

I've been following this forum for some time & I'm sure there are a good

number of you guys ,& Gals, who know this as just "Old stuff". This is

driving me nuts.. HELP!

The temp in the interior, right? I ask because 120°C is the overheat point for the engine on the gauge .

__________________
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1982 300SD -- 211k, Texas car, tranny issues ____ 1979 240D 4-speed 234k -- turbo and tuned IP, third world taxi hot rod

2 Samuel 12:13: "David said to Nathan, “I have sinned against the Lord.” And Nathan said to David, “The Lord also has put away your sin; you shall not die."

Check the coolant level with the engine running.

Replace the damaged Mono valve.

.

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Dynamometer.
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1985 300SD
1983 300D
1984 190D
2003 Volvo V70
2002 Honda Civic

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The 120 F is on a thermometer in the vent. Air temp coming into the cab.

Coolant is ok.

Thanks for the comeback & opinions. I'll check the Mono too. I had one

replaced about a year ago,...could be damaged. I disconnected the aux

pump when I read they could take out your control.