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R172 CDI 2013 - Interior cooling temperature issues

HairyRichard69

New Member
Joined
Feb 15, 2025
Messages
1
Location
Kent
Car
SLK 250 CDI
Hello everyone!

I have an issue with my SLK 250 CDI R172 2013 in which the temperature of the interior heating cycles from hot to cold without any change/input of the dials.

I can leave the car temp at 24c to heat the cabin etc and it is nice and hot, and the heating will suddenly go cold and stay that way for a few mins, before then going back up to hot.

It cycles the temperature periodically without any input from me, and it seems to resolve itself by just leaving it cycling air in the cabin to then go back to hot.

Changing the dials does nothing, nor does turning AC on/off.

Anyone had this issue before. Any ideas what it might be?
 
There is a heater control valve that can fail. It's usually on the bulkhead with two pipes going in and out of the valve.
 

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