We've had a heatwave in the N.E. recently. But while driving my wifes '87 300D the other day it was raining.With the windows up the windshield started to fog over.I pushed the defrost button.
Of course the fan blows full blast(normal) but the temp. dial was at full cold and it was cranking FULL HOT!My condenser is broken as of now but it did this when the A.C. was working fine too.
Also when allowing her to warm up in the morning i depress the
"0" (off) button.I hear a click and the fan continues to blow.
I know this climate control is the bane of MB's but there's got to be some way to T.S. this system before replacing these expensive parts.I have searched the previous posts but have not found a problem similar to this. TIA. JOE........

I was wondering about that. Even in Texas in the middle of August you have to blast heat from your defrost?
Odd setup wouldn't you say ?

There is a way to get defrosting and cool air and that is the Hi/Lo button or the one under the defrost button. I found that i get some split airconditioning that way. As for the fan running on. I noticed that mine would do the same thing for a short while after selecting off. I think it's similar to the system taking several seconds to start blowing depending on the outside/inside temperatur. I could be wrong, but I did notice the same thing but ignored it as long as the thing worked.

My 84 300D had a similar problem Friday on our camping trip. All of the sudden the vent started blowing hot.

Turns out I had blown a fuse that controlled both the horn and a heater control.
Replaced the fuse and the cool air was back.

I think I have a short in my horn somewhere.

__________________
84 300D 251K
87 190DT 281K - Sold
06 Ford Escape 172K
94 Ford Ranger 250K
99 Chevy Suburban 181K

Larry Bible, credit goes to him, gave me a tech bulletin that has great troubleshooting tips for ACC.

Post your fax number or send me a private message and I'll fax it to you.

JCD

My brother's 300SDL did the same thing -- low speed only on fan, hot air out the defrost vents only. Turned out to be the fuse had died of old age and corrosion.

This was in the winter, like to froze my feet!

Peter

__________________
1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!