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Blower Control Circuit Diagnosis: Notes

The blower control can be divided into two categories: blower turn-on and blower speed control. Blower turn-on is accomplished when a ground path is completed. Relay coil grounds are completed by (a) the heater turn-on switch which provides delay for heater water warm-up in winter operation, (b) the in-car switch which provides immediate turn-on in summer operation, or (c) manual override in the "DEF" position.

Blower speed control is accomplished by circuit board lever connections in the "Off" and "Lo" blower positions, by selective use of the resistors on blower circuit board when in "ECONOMY", "AUTO", and "BI-LEVEL", or by high blower override circuit in "HI" and "DEF".

It should be noted that system air doors are always positioned to allow delivery of air into passenger compartment. Problem descriptions and probable causes are listed:

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