I have a problem we cannot diagnose.

Only on extended runs (45 minutes or more driving, typically on Highway) will the Heat or A/C stop blowing. I hear the fan running and responding to different blower selections but it is as if thevent doors have shut and airflow iseliminated. On local use the HVAC works fine.

Anyone have this problem?

 

Strangely my car w220 S320 starts to blow cold after about a 30 - 45 mins.

I don't like Auto Climate Control since this blows too much air to the screen and centre vent.

The problem however occurs on both Auto and Manual settings. I like my feet warm...rather HOT.

Never got round to trying to find out what is going on. Suspect the footwell flap shuts possibly because the top of the car is up to temp. Not sure.

Let us know what you find. The Air Con Cooling works fine. All we need is some HOT weather!!

Stuart

 

When my problem is occurring, the cabin temp. either cools or heats to an undesirable leveldue to air flow cut-off (as if the vents have closed but the system or rather fan isstill blowing).

From what I can tell, the HVAC is not changingtemps. on me, justturning off the circulation and the cabin temps responds since it is left to ambient airinfluence (the outdoor elements).

 

use a star diagnostic computer to find out the fault code, that is the only scientific way to approach the problem, start from there and inform us on the fault code, sometimes it may be the climate control module, but I would rather start with the fault codes before spending money on the expensive part. during the 1992 to 1996 they have been producing defective control modules and they have already revised it code 20

 

No valid fault code present!

MB Number 220 830 01 85 HW version 41.1998 SW version 40.1998 Diagnosis version 2/04 Pin 1
Code B1000 Control Unit N22 (AAC pushbutton control module) is defective.
Important Note: This fault can be ignored for control units with MB No. 220 830 09 85 and a SW version older tha 10/01

So what next! and why does this code NOT apply to early cars I wonder? What was the change made at 10/01 and why did this introduce the B1000 code problem. More to this than meets the eye!

System warms up, cools down absolutely fine but after an extended period the car starts getting too cool (in cold weather) necessitating that temp is increased. In my case it is the air to the footwell that is the problem since I prefer to select this manually. Passenger experiences the same problem as the driver.
Rear passengers seem OK but maybe they don't know any better!

To save referring to WIS what controls the footwell flap.
Electric or vac servo?
Where is the footwell temp sensor located please?
What does the signal look like and is it proportionatly controlled or just ON/OFF.



Stuart.

 

My dealer advised they were not getitng a fault code so could not proceed unless I duplicated thei problem on the raod and drove immediately to my delaer, which I am planningon doing the next time I take a highway or extended trip.

In the mean-time, any other ideas?

 

I get heat out of left vent with AC on. Any way to diagnose this problem?