System Check - Air Delivery & Temperature Controls

PERFORM BEFORE BEGINNING SYSTEM DIAGNOSIS
1. Air flow out of the Defroster Duct only is an indication of no vacuum present at the Heater/Vent/Air Conditioning (HVAC) Programmer.
2. If the Air Mix Door is disturbed for any reason, you must disconnect the Battery or the HVAC Programmer momentarily to start the calibration sequence. During the calibration process the Blower Motor will not operate for approximately 1 1/2 minutes.
3. After an Outside Temperature Sensor has been changed or is open, the external temperature will read -50°F and Diagnostic Trouble Code (DTC) 03 will be set until the vehicle has been driven over 25 mph for 3 minutes.
4. The Outside Air Temperature Display will not increase until vehicle is driven over 25 mph for 3 minutes.
5. If a low Freon DTC 09 is set, the A/C Compressor will not operate. To reset this DTC, disconnect Battery or pull the A/C PROG Fuse, then reconnect.

(Engine warm and running in idle)
6. Check manifold vacuum at the Black hose from the Engine on the Vacuum Tank.
^ If vacuum is not present, check the hose back to the Engine Vacuum Source.
^ If vacuum is present, check for vacuum at the Black hose at the HVAC Control Head. If there is no vacuum at the HVAC Control Head, replace the Vacuum Tank.
7. Check that the vacuum hoses from the HVAC Programmer to the Vacuum Actuators are connected and in good condition.
^ Refer to the A/C System Check for a guide to normal operation and diagnostic references. Testing and Inspection
^ 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).
^ Check for proper installation of aftermarket electronic equipment which may affect the integrity of other systems (Refer to General Troubleshooting Procedures). Diagnostic Aids
^ Refer to System Diagnosis. Controls System - HVAC System - Electronic