Blows hot air from A/C vents?

SUHAILKADER

MEMBER
1997 MERCEDES BENZ S320
3.0L
V6
4WD
AUTOMATIC
130,000 MILES

Blows hot air from driver side top A/C vent. All other vents blow cold air, but pressure is not up to the limit. Replaced heater core assembly with used one. And bypassed the duo valve by connecting the heater hose with water pump. Replaced Climate Control Vacuum Valve Block with used one but, now all vents blow hot air. Sometimes there is noise due to air leaking around the block (not all the time). Removed the battery and reconnected after 30 minutes then it's works fine sometimes. Looking forward to some solutions.
Thank you.

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1 Reply

KEN L

MASTER CERTIFIED MECHANIC
47,690 POSTS

It sounds like the HVAC controller has gone out, which is common. Also, the fact that you can reset it and it works for a while is another indication of the HVAC module going out, but I would run a scan on the HVAC system to see if any codes are stored, this guide can help. You can get a CAN scanner (Controller Area Network) which will work on most cars from Amazon.

Here is a video to show you how:

https://youtu.be/u-4syLc-ifQ

Here is how to change the HVAC module out in case a code is stored for it. I am not sure what part you have uploaded in the images. Can you please tell me where it came from? Check out the images (below). Please upload pictures or videos in your response to any problems so we can see what to help you with.

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