Troubleshooting Hints - Heater - Without A/C

FRONT
1. CHECK the condition of the HTR-A/C Fuse 12 and the HVAC Fuse. If either fuse is open, LOCATE and REPAIR the cause of the overload and REPLACE the fuse(s).
2. CHECK that Ground G103 is clean and tight.
3. If the Front Blower Motor operates only in HI speed, then REPLACE the Blower Motor Resistor/Relay.
4. If the Front Blower Motor operates only for a short period of time in LO, Medium I, or Medium 2 speeds, stops, then starts again, the thermal fuses are opening and resetting automatically. REPLACE the Blower Motor.

REAR AUXILIARY
1. CHECK condition of RR HVAC Fuse 24 , HVAC Fuse and the RR BLOWER Fuse. If any fuse is open, LOCATE and REPAIR cause of overload and REPLACE Fuse(s).
2. CHECK that Ground G400 is clean and tight.
3. CHECK that the three Auxiliary Blower Motor Relays are properly mounted in their connectors.

GENERAL
1. See Lighting and Horns for diagnosis of the Instrument Panel Dimming illumination lamp circuits. Lighting and Horns
^ CHECK for a broken (or partially broken) wire inside the insulation which could cause system malfunction but prove GOOD in a Continuity/Voltage check with a system disconnected. These Circuits may be intermittent or resistive when loaded, and if possible, should be checked by monitoring for a Voltage drop with the system operational (under load).
^ CHECK for proper installation of aftermarket electronic equipment which may affect the integrity of other system (Refer Troubleshooting Procedures). Diagnostic Aids