Torn Mono-valve Diaphragm (Heater Control Unit)

If you own a 1981 to 1991 123, 107 or 126 chassis and have not heard about the mono-valve then this alert should be a real help. This little valve controls the amount of hot water going into your heater core. The seal for the valve is made of rubber. With age this rubber splits and will cause your heater to go wacky. It will generally get hot when you want it to be cold and in some cases it acts like it has a mind of its own. Failure of the mono-valve has often led to some big repair bills for the unknowing. This part is very inexpensive, can easily be replaced by yourself, and in 7 out of 10 cases will most likely solve you sporadic heat problems.

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