System Operates Only At Max A/C

May be caused by vacuum or electrical problem.

1. With system operating, disconnect programmer electrical connector and observe programmer movement through slot at bottom of programmer cover.
2. If programmer remains in Max A/C position, remove multiple vacuum connector and check for supply vacuum at black hose.
3. If no or low vacuum, check for Teaks or disconnects in vacuum hose routings. Refer to appropriate vacuum diagram in separate articles in this section. 
4. If vacuum is okay, programmer is malfunctioning. Remove cover and inspect for obvious defects. If none are visible, use ATC Tester J-23678 to analyze and correct problem (complete programmer testing instructions are furnished with test unit).
5. If programmer moved to Max Heat position when electrical connection was removed, defect is external to programmer. Check the following items:
   • Shorted in-car sensor.
   • Shorted or miscalibrated temperature dial.
   • Short in sensor circuit of wiring harness.
   • Disconnect or open in ground circuit (black wire) between control head and programmer.
   • No electrical power to programmer (yellow wire).
   • Malfunction within programmer assembly.