Test I: Insufficient, Erratic Or No Heat

PINPOINT TEST I: INSUFFICIENT, ERRATIC OR NO HEAT

NOTE: Electronic automatic temperature control (EATC) systems only.

Normal Operation
Under normal operation, the automatic temperature control (ATC) solenoid and manifold receives a ground from the HVAC module - EATC through circuit RH226 (WH/VT). When the heater control valve vacuum solenoid is to be energized, the ATC solenoid and manifold receives voltage from the HVAC module - EATC through circuit CH224 (BU/OG).

NOTE: Manual climate control systems only.

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.

This pinpoint test is intended to diagnose the following:
- (EATC systems only) An open, short to voltage, ground in circuit CH224 (BU/OG)
- (EATC systems only) ATC solenoid and manifold
- (EATC systems only) HVAC module - EATC
- (Manual climate control systems only) Function selector switch
- Heater control valve
- Heater control valve vacuum switch (if equipped)
- Stuck or bound linkage or door
- Leaking or plugged vacuum hose
- Temperature blend door actuator

I1-I3:

I4-I7:

I7-I9: