HELP! My air conditioner blows HOT air!
No, I'm not just complaining because it is not "cold enough". It is not cold at all... It is not cool... It is not even warm!! IT IS HOT!!!!! I live in Georgia and we haven't even come close to what we consider "hot" down here. But with the temperature being in the high 80's (for now) it gets pretty damn hot inside a car that is blowing hot air. I've tried EVERYTHING! and the P.O.S. air conditioner will not even turn off, which makes me wonder where the problem really lies. My engin temp is normal, my car has never overheated, No signs of any real trouble untill now.
Please Help Me!?!?!? I'm pretty sure I could catch on fire and melt away any day now.

What model Benz do you own?

The symptoms that you listed suggest that the air system has switched into "default mode". Mercedes, always safety minded, sets the A/C to blow hot defrost air if a problem arises in the sir conditioning system (so you can at least see out of your scalding car).

You may need a new electronic a/c circuit board. Not a huge repair cost. It could be worse, your evaporator could be leaking - that's a $2,000 repair or worse.

Please let us know more about your car and symptoms (where is the air coming from?) and we'll help as best we can.

Troy
1995 E420 82k

Yes, for this one we need to know what year and model. I remember your picture and your cat, looks like mine, but I can't remember what year and model MB you have.

Good luck,

year and model of car in her profile

Her profile says 1990 300E.

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Jim

The aux pump can run like crazy and not flow unless the heater valve opens. The aux pump could, indirectly, easily be the cause of the whole thing.

As the aux pump gets old and cruds up, the current draw increases. When it gets too high it will blow the climate control pushbutton unit. This will cause loss of signal to the heater valve. Since the heater valve is normally open, you will get max heat with no mercy.

Start by blocking the flow to the heater valve and see if the heat goes away. If so check for any signal going to the heater valve. If there is none, the CCU likely needs replacing. If you replace it, check aux pump current draw so that it does not blow the new CCU. If the aux pump current draw exceeds 1.3 Amps, replace that aux pump at the same time.

Good luck,

Yall are just sooo helpfull!!!!
Now I just REALLY wish I understood your o-so appreciated advice. I'll eventually get it. I will certanly keep yall updated with the progress. Thanks so much! And if you think of anything else you want to tell me I will keep coming back to this post... or you can e-mail me!
Iminluv07@hotmail.com Keep being amazing and kind!!! Yall are great!

I've got a similar problem yesterday....

That is, I was sitting in the parking lot, key on, blower working at full speed with fresh air. Then, just after I started the engine, the windshield+side vents on the left side began to blow hot air (left temp wheel was set on minimum, as usual), while the right side kept on working properly.

Now, if this was a problem with the heater valve, it would pour heat from all vents, yet the right side worked properly. In cars with no A/C, temp can be set separately for right and left from the two wheels, that is, one can set the left on 22C and the right on 18C, and the system blows two separate flows of air, right and left.

That is, I've closed the left side vents... and I'd wish to know what to do

~Thank you

Nautilus

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1990 260E Sportline (that's 300E 2.6 for our American friends) -> sold
2001 E320 4Matic Elegance -> my Dad's daily drive
2005 Seat Leon FR 1.8T

If the blower is running at the correct speed (fast on high, slow on low), the monovalve is likely failed and staying open or the PBCU is fried (as Larry said, could be the aux pump drawing too much current).

If you don't have a blower at all, just blistering hot air, the fuse in the fuse box under the hood is bad and you have no climate control all. Replace all the fuses, they are getting corroded by now.

If a new fuse fixes the heat but not the blower, check the strip fuse for the blower, it's in a small snap top black box just in front of the fuse box, just a metal strip held down by two screws. Chances are, it will be cracked so that when you touch it, it will bend apart. Costs about $0.50.

Peter

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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!