Chart 1C-7 Improper Defogger or Heated Mirror Operation

Diagnostic Chart:

Wiring Diagram:

CIRCUIT DESCRIPTION

When the ignition switch is turned to "RUN," voltage is applied from I/P Fuse Block Fuses 33 (C68) and 20 to the H-A/C control. When the rear defogger switch is pressed to "ON," voltage is momentarily applied to the defog request input of the solid state timer. Once requested, the timer will close the internal contacts from terminal "D15" to terminal "C1" (C68) or terminal "A1" to terminal "A8" (C67) of the H-A/C control, lighting the "ON" indicator and energizing the coil of the rear defogger relay with voltage applied from I/P Fuse Block Circuit Breaker 4 and CKT 1640 to CKT 293, and I/P Fuse Block Fuse 1 to the heated mirrors.

The solid state timer with the H-A/C control will control the time the internal contacts are closed. When the ignition switch is turned to "RUN" and the rear defogger switch is turned to "ON" for the first time, the defog cycle lasts 10 minutes. Further operation will result in 5 minute defog cycles. The defog cycle is reset to 10 minutes when the ignition switch is turned to "OFF" and back to "RUN."

DIAGNOSTIC AIDS

1. Check I/P Circuit Breaker 4. If open, check for short to ground in CKT 1640.

2. Check the rear defogger grid for opens.

3. Check that grounds G201, G202. or G300 and G400 are clean and tight.

4. If both mirror defoggers are inoperative but rear defogger operates normally, check I/P fuse. If open, check for a short to ground in CKT 676.

5. Check I/P fuse 11. If open, check for a short to ground in CKT 39.

6. Check I/P fuse 33 (C68). If open, check for a short to ground in CKT 40.

7. Check I/P fuse 20. If open, check for a short to ground in CKT 241.

8. Check for a broken or partially broken wire inside of the insulation which could cause system failure but prove "GOOD" in a continuity voltage check. Refer to Diagrams / Diagnostic Aids. Diagnostic Aids

9. Check for proper installation of after market electronic equipment which may affect the integrity of other systems.