heater blows sometime

1992 CADILLAC DEVILLE
231,205 MILES • 4.9L • V8 • FWD • AUTOMATIC
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REARDRIVE
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  • 93 POSTS
Sometime I start the car turn the heater on it will blow fine but when I turn the switch off, when I restart the car the heater blower will not blow. A day or two it may start back blowing. I put on a new thermostat and a new T tube
Jan 7, 2017 at 4:07 PM
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CARADIODOC
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That is the classic symptom of worn brushes inside the fan motor. A clue is it will often start working when you bang on the heater box. Once it starts running, it will not fail to continue running until you turn it off.

It is possible for an overheated connector terminal or fan speed switch to cause intermittent operation too. but those do not take long before they become a permanent failure.
Jan 8, 2017 at 3:02 PM