450 SL heater problem..help please.

Heat is always on. Temp control wheel on dash seems to have no effect. Any advice on solving this problem would be greatly appreciated.

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You don't specify the year of this car. The '76 - '80 models have an "amplifier" (logic board) which controls the system. The board's solder joints crack with age and its logic becomes insanity.
These amplifiers can be bought remanufactured for about $100. You need to find this cigarette pack size unit with a black perforated metal cover and lots of wires plugged into its base - suggest you remove the glove box and look behind it - that's its location in the 116 and 123 sedans.
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