Tech 1 Diagnosis - HVAC System - Automatic

This procedure provides an overall check of the Heating and Air Conditioning System.

Complete the test with the Engine idling and the temperature outside the vehicle at 60°F (16°C) or higher. Set English-Metric Switch to "ENGLISH."

When the Ignition is first turned "ON," the Heating and A/C System may run the Blower at low speed with air flow from the Floor Outlets. This operation will last for 15 seconds. This is done to purge the heater core of moist air to prevent the windshield from fogging. It will occur only when the Heating and A/C System program determines that the outside and inside temperature are low enough to require it.

If the Heating and A/C System detects a fault in one of the system components, it will be indicated by a flashing MODE Indicator when the Ignition Switch is first turned "ON." If indicator is flashing, refer to
A/C and Heating section.

A no blower operation condition will occur for 1-1/2 minutes while the Air Mix Valve Actuator recalibrates. Recalibration will occur whenever the Battery, Heater and A/C Programmer or Air Mix Valve Actuator has been disconnected.

^ If the Heater and A/C Control Head or Programmer appear completely inoperative, perform Chart #2 - Heater and A/C Control Head and/or Programmer Inoperative.

IMPORTANT: Disconnect the negative battery cable for 15 seconds before performing Chart #2 as this may correct the problem.

TECH 1 DIAGNOSIS

Vehicle Preparation
^ Connect a jumper wire from the Heater and A/C Control Head Connector, terminal "4" or terminal "5", to the ALDL Connector, terminal "J". Insert the jumper through the back (wire entry side) of each connector.
^ Install the Tech 1 using the Body Systems Cartridge. When the Tech 1 asks for the model year, key in 1990 (not 1992)).
^ Proceed with climate control diagnosis.

Important: To prevent future data line communication problems, remove the jumper wire after diagnosis.

A/C System Check - Electronic A/C:

A/C System Check - Electronic A/C: