Initial Inspection and Diagnostic Overview

Due to the interactions of all heating, ventilation, and air conditioning functions in an Automatic Temperature Control (ATC) system, it is essential that the entire climate control system be checked to fully analyze the proper failure condition(s) and isolate the inoperative components(s). After a preliminary check to verify the complaint, a check of the supporting systems should be performed:
^ Heat to heater core.
^ Refrigerant to evaporator core.
^ Air distribution for proper location and quantity.

SYSTEM CHECK
Test Conditions:
^ Engine warm and above 1200 rpm.
^ Vehicle interior 24° C ± 3° C (75° F ± 5° F).
1. Check air distribution for proper operation in each function. If a fault is found, it must be corrected before proceeding to the ATC checkout.
2. Set the function selector to the VENT position. Check the blower operation in low, medium, and high. If OK, move the selector to AUTO. If the blower does not operate properly in all the manual positions, correct the inoperative component and proceed. Refer to the Auto Blower Diagnosis Chart. Auto Blower Diagnostic Chart

ATC Performance Check At 75 Degrees F +/- 5 Degrees F:

3. Cycle the temperature lever from 65° F to 85° F and observe the blower speed change and discharge temperature change. The chart shows the relationship of these functions.
4. Move the temperature lever back to 65° F and observe the blower and temperature outputs.
5. With the temperature lever still at 65 ° F, move the function lever to A/C. The fresh air/recirculate door should open and the A/C compressor clutch should engage to produce colder discharge temperatures.
6. Move the temperature lever to the 22° to 24° C (72° F to 75)° F position. The blower speed should reduce down to low or medium-low and the discharge temperature should rise to a more moderate level.

COMPONENT CHECKS
This will identify the inoperative component based upon the complaint or system failure condition.

Component Identification
Vacuum controlled ATC malfunctions can be divided into three groups:
1. Improper discharge temperature control.
2. Improper blower speed control.
3. Improper system inlet control.
The most common causes of failures in the system are vacuum leaks (these leaks can be anywhere in the vehicle), cable adjustments, and aspirator hose connections. The following is a detailed checkout procedure to fully analyze the ATC system and isolate the inoperative component.

Test Equipment
^ Vacuum gauge, 0-30 in Hg, 0-30 in Hg, Rotunda model 059-00008 or equivalent.
^ Voltmeter, Rotunda model 007-00001 or equivalent.
^ Continuity tester.

Test Conditions
^ Engine Warm (run at least 10 minutes).
^ Engine above 1200 rpm.
^ Vehicle interior 24° C ± 3° C (75° F ± 5° F).

Perform the Vacuum/Blower/Temperature Response Test. Vacuum /Blower/Temperature Response Test