Test B: Insufficient, Erratic Or No Heat

PINPOINT TEST B: INSUFFICIENT, ERRATIC OR NO HEAT

B1-B3:

B3-B5:

B5-B7:

Normal Operation
Under normal operation, the function selector switch receives engine vacuum. When OFF or MAX A/C is selected, vacuum is applied to the recirculation vacuum control motor. When the temperature is in the full COOL position, the heater control valve vacuum switch applies vacuum to the heater control valve.

Possible Causes
- Function selector switch
- Heater control valve
- Stuck or bound linkage or door
- Leaking or plugged vacuum hose
- Temperature blend door actuator