My 1991 300D heater only blows warm air , not hot like it used to do. The engine temperature reads normal.
The fan has to run a long time and fast to warm up the car. When it does get warm it does regulate the temperature in the car.

Any ideas?????

Low coolant level - what the heck, this is easy to check, even if no caution light is on

Malfunctions in controls:
- monovalve internal problem not allowing enough flow
- cabin heat sensor not asking for enough heat
- heater sensor sensing more heat that delivered

I'm all out of ideas at this point.

Most of the time this is low coolant, as Jim
pointed out, or air in the coolant.

Besides problems with the cabin controls,
could be a bad thermostat.

Also could be the aux coolant pump. That is
an electric pump that assists circulation of
coolant at low engine speeds such as when
in town traffic. Check whether the problem
occurs if you are on the freeway when
warming up.

Had the same problem in an 85 500 SEL. Was told by trustworthy indy mech. these are pretty complicated sytems. Do not think settings are cable driven like older cars. Could be all or none of the problems listed in 2nd post. Costly to find. In my case, at least the seat warmers worked well enough to bake"buns"! Good luck if it is cold where ever you are.

I would check the aux pump. You can put your hand on it and feel if it is running. When my aux pump decided to stop working due to a bad climate control unit the heater never got hot like it used to. Even when on the highway. I jumpered mine to force it on but I will not tell you how as I got reamed already once last week for suggesting some one pierce a wire to test it. On mine it seems the ground side is controlled by the HVAC unit in the dash and mine was no longer grounding that line to activate the pump.

__________________
~Jamie
_________________
2003 Pewter C230K SC C1, C4, C5, C7, heated seats, CD Changer, and 6 Speed. ContiExtremes on the C7's.

1986 190E 2.3 Black, Auto, Mods to come soon.....