Chart 1C-7 Improper Defogger or Heated Mirror Operation

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 Fuse 11 and CKT 39. When the rear defogger relay contacts close, voltage is applied from I/P Fuse Block Circuit Breaker 4 and CKT 1640 to CKT 293, and I/P Fuse Block Fuse 44 to the heated mirrors.

The solid state timer within 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 pushed 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 and G300 or G400 are clean and tight.
4. If both mirror defoggers are inoperative but rear defogger operates normally, check I/P Fuse 44. 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 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).
9. Check for proper installation of aftermarket electronic equipment which may affect the integrity of other systems.