ACC heat /cool mode backards? - Page 2 - PeachParts Mercedes-Benz Forum

nomorehurry · #16 04-19-2011, 02:09 PM

Quote:

Originally Posted by tangofox007

"Now" is how I read it. The difference would be in how the air is distributed, not in the temperature of that air. I don't think the uncommanded heat problem is in any way related to the defrost air distribution..

With the defroster, what I found was that cool air was comming from the defroster vents to the in-car temperature sensor. The sensor read the cool air and sent an incorrect message to the CCU (car is cold - turn on heat). Result, heater came on until in-car sensor told CCU that car was too hot. Unfortunately the car had to be stopped to allow something to reset and go back to cooling mode.

Anyway, it did have to be fixed and only cost $10 (U-pick part) and some bad words to get it installed. However, experience from the u-pick place in taking the vent control out was of great help in putting the new (old but working) part in.

Now the system seems to be OK except that this morning the air conditioner stopped and sent slightly warm (not hot!) air to the cabin instead of the cooled air. After allowing the car to rest for a while, everything went back to normal and stayed that way until I god home, which was a longer trip. I'm thinking that might be the high temperature shut down for the compressor, which I think has already been replaced once.

If the d*** machine would be consistent, it would be a lot easier to trouble shoot. (the word "shoot" is starting to sound better the more I work on this thing.

)

PS: In case I didn't say it before, I appreciate your assistance.

tangofox007 · #17 04-19-2011, 02:27 PM

Quote:

Originally Posted by nomorehurry

With the defroster, what I found was that cool air was comming from the defroster vents to the in-car temperature sensor. The sensor read the cool air and sent an incorrect message to the CCU (car is cold - turn on heat). Result, heater came on until in-car sensor told CCU that car was too hot.

The temp sensor should not be a factor in the "defrost" mode. The ACC should engage the compressor and provide maximum heat, regardless of temp selected.

Quote:

Originally Posted by nomorehurry

Now the system seems to be OK except that this morning the air conditioner stopped and sent slightly warm (not hot!) air to the cabin instead of the cooled air. After allowing the car to rest for a while, everything went back to normal and stayed that way until I god home, which was a longer trip.

That sounds a lot like a faulty evaporator temp regulator.

Quote:

Originally Posted by nomorehurry

I'm thinking that might be the high temperature shut down for the compressor, which I think has already been replaced once.

The original configuration had no such feature.

nomorehurry · #18 04-19-2011, 04:33 PM

I agree that you should get full heat in the defrost mode.

However, I was in the regular central vent (button 3) mode and should not have had any flow through the defroster vents. But I was still getting cold air that would fog the inside of the windshield (given more than the 9% humidity in west texas). Thats why I think it was the air cooler flow from the defroster vents that led to incorrect information to the CCU.

I guess I didn't make the situation clear earlier.