Chilly heater in 1983 300TD

My 1983 300TD passenger compartment heating system leaves something to be desired now that cool weather has arrived. I get warm air in the "EC" mode only for a short time, at which time the unit starts blowing cool air. If I turn the blower to the "low" setting, I get warm air again but only for a few minutes before it reverts to cool air. If I turn the temperature wheel to the highest setting (past the "click") I get continuous warm (not hot) air but only with the fan set at "low". This effect is particularly noticeable at highway speeds.

My ACC pushbutton assembly is relatively new (rebuilt) and I replaced the thermostat so the engine runs at a normal operating temperature (80+). What steps should I take to trouble shoot this problem before it gets REALLY cold outside? I am not the only one with this problem and we are both currently STUMPED!

Andrew
1983 300TD
252K miles
Andrew

[ctaylor738]

When we had this problem in our '82, it usually turned out to be the mono valves.

Chuck

Chuck: I was told by someone on the Diesel list (diesel@mbz.org) that a new monovalve repair kit will solve the problem of continuous heat, not what I described. Tell me more...

BTW - I tried Silver Star and was truly impressed by their friendly service and the quality of their work. Thanks for the tip!!

quote:

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Originally posted by ctaylor738:
When we had this problem in our '82, it usually turned out to be the mono valves.

Chuck

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1983 300 TD (his)
1969 280SE 3.5 coupe (his)
1985 300 CD (hers)

My money is on the monovalve at almost any odds.

You can get a repair kit for a little over $30 and it takes only about five or ten minutes to replace.

Good luck,

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Larry Bible
'01 C Class, Six Speed
'84 Euro 240D, manual, 533K miles
'88 300E 5 Speed
'81 300D Daughter's Car
Over 800,000 miles in
Mercedes automobiles

OK, at that price I'll purchase the kit. Now the $64 followup question is --- where is the monovalve located?

Andrew

quote:

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Originally posted by LarryBible:
My money is on the monovalve at almost any odds.

You can get a repair kit for a little over $30 and it takes only about five or ten minutes to replace.

Good luck,

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