Troubleshooting Hints - HVAC System - Automatic

Temperature control problems can result from refrigerant faults, electrical wiring or vacuum faults, mechanical faults (i.e. sticking valves) and/or heater and A/C control assembly faults.

The automatic control air conditioning system can electronically identify several system faults. When the heater and A/C control assembly first detects a fault, the set or outside temperature displayed flashes for approximately two minutes during each ignition cycle until the fault code is corrected or cleared. If this occurs, the diagnostic mode can be entered and the display on the heater and A/C control assembly show a number which represents a particular fault or circuit.

For diagnosis of refrigerant, vacuum, and mechanical faults, Refer to System Diagnosis / Procedures / Functional Test. Testing and Inspection

For additional A/C clutch diagnosis, Refer to Powertrain Management / Computers and Control Systems / System Diagnosis / Procedures. Testing and Inspection

Often, a fault which is not identifiable by self-diagnostics can be located quickly by performing a thorough visual inspection of underhood components, electrical harnesses, and vacuum hose connections.

If the programmer must be tested, be sure to keep it vertical to enable gravity to close off all vacuum supply through the solenoids not activated by the heater and A/C control assembly.