W202 Heater temperature unstable.

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Active Member
Aug 19, 2011
Belfast, N. Ireland
ML320 and CLK200K Cabrio
Had the car a few weeks now. Got the A/C recharged, it needed it badly.

Now I can't get the heater to sit at a stable temperature. A nanometre change in the temperature control seems to go from fantastically hot to fantastically cold or vice-versa. Even looking at the temperature control sternly causes this disconcerting effect.

It's the manual control version with the two temperature controls. Any ideas?
check the control valves two of them under the bonnet
Will do.

The thing is. If I leave the temp dials in one place one day I get cold air out and the next I get warm out, next day it might be warm, it might be cold. Completely random.

So I would think the valves are working but whatever controls them is a tad confused.
Last edited:
the valves near the brake servo drivers side have electrical solenoids check the wires but these valves are the most common fault

other then that get the codes read fastest way
Righty ho.

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