Hi Jeff

I am not an expert nor am I familiar with your particular model.

Merc heating is normally controlled independently for each side.

The control wheel activate a potentiometer which in turn via the control circuit drives one element of the 'duo valve' which allows more or less water (at engine operating temp) through the heater matrix.

I drive an 'old' 230 TE and the driver side heater control is lazy and I often have to kick it into action by winding the control wheels on both sides from stop to stop until it eventually kicks in.

I have promised myself to strip out the control board and give the potentiometers a squirt of pot cleaner and lube - but you know how it is - there are just so many things to do and so little time;-)

I am sure an expert will pop up and do better for you.

Good luck - in the meantime wear really thick socks!!

NormanB

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NormanB
230 TE (W124) 1989 with 153,000 miles on the clock - hoping for at least another 100K