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21 Aug 2020

Heater blower replacement part two

Guy White's guide to replacing the heater blower motor part two

Last month I detailed how I replaced the heater blower motor in my 1974 Carrera 2.7 restoration project. Heree is part two. Originally the motor had not been turning at all and, despite trying to free it off with some WD40, I was not able to get it working satisfactorily. Changing the motor got it going again successfully, but I then found that the fan was operating at full speed on both the medium and high settings. (There are three speeds that can be selected.) The power to the motor is routed directly to the motor on the high setting and through two coiled resistors to limit the speed on the low and medium settings respectively. However, I also discovered that the two resistors each have a bi-metallic strip contact connected in parallel with them. The function of the bi-metallic strip is to close a contact if the resistor gets too hot diverting the current through this and turning the fan to the high setting to cool the resistor. I therefore cleaned the contact with a piece of fine emery cloth and bent the bi-metallic strip to ensure a small gap across the contact and everything now works perfectly.

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