Since I've owned the car it would blow only hot air when in the defrost mode.
Now, even with all switches off, it blows hot air from the dash vents.

Hot enough that the plastic vanes of the vents are too hot to touch for long.

This might be nice in the dead of winter, but a black car with no A/C in the summer? Not so much.

No amount of temperature wheel changes, fan settings, or mode switching changes anything.

Tips please.

__________________
Albany, NY Suburbs
'87 300D

my control unit (wheel/buttons) has been replaced 3 times. it would just blow very hot air at all times, any vents

the third one has worked for over 2 years now, hoping its my last. you may try pulling one from a junk yard

87 300D

duncwarw,

DeFrost is the DEEFAULT mode for ALL Mercedes HVAC systems. (SAFETY)

[If you're lucky the HOT AIR is a BAD Mono-Valve allowing HOT Coolant
to enter the HVAC.]

Chances are your CCU ($$$$$$.$$) @ a dealer is BAD.

OR

Your "Pods' are gone

ALONG with AIR CONDITIONING system Woes.

LOTS of Info @ the Advanced search Button:

http://www.peachparts.com/shopforum/search.php?searchid=5025762

__________________
'84 300SD sold
124.128

Thank you all. I'll let you know what I find.

"Compress", thanks for the link. It didn't work for me but I'll try once again to work with the search function.

__________________
Albany, NY Suburbs
'87 300D

yeah, C.I. that link isn't working...