Initial Inspection and Diagnostic Overview
Automatic Temperature Control (ATC)Due to the interactions of all heating, ventilation and air conditioning functions in an Automatic Temperature Control system, it is essential that the entire Climate Control system be checked to fully analyze the failure condition(s) and isolate the inoperative components(s) (Fig. 26). After a preliminary check to verity the concern, a check of the supporting Systems should be performed:
^ Heat to heater core
^ Air conditioning clutch operation
^ Air distribution for proper location and quantity The following is divided into two parts. The first part contains a general checkout procedure to be used when the fault is not fully defined or more than one concern exists. The second part contains a detailed checkout procedure to isolate the condition to a component.
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 fault is found, it must be corrected before proceeding to the ATC checkout.
2. Set function selector to VENT position. Check blower operation in low and high. If OK, move selector to AUTO. If blower does not operate properly in all positions, correct inoperative component and proceed. Refer to Blower Speed Controller Diagnosis.
3. Cycle temperature lever from 65°-85°F and observe blower speed change and discharge temperature change. The chart in Fig. 11 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 NORM A/C. The outside air/ recirc door should open and the A/C compressor clutch should engage to produce colder discharge temperatures.
6. Move the temperature lever to 72°-75°F Blower speed should reduce down to low or medium low and the discharge temperature rise to a more moderate level.
Fig. 27 ATC Performance Check At 75 Degrees +/- 5 Degrees - Interior Temperature:
Figure 11 ATC Performance Check At 75 Degrees +/- 5 Degrees Interior Temperature:
Insufficient or No Heat
Observe servo vacuum with temperature lever at 85°F. If 3 in-Hg or lower, check for hot heater hoses to and from heater core and that servo positions blend door in full heat position. If over 3 in-Hg., disconnect line from servo and note discharge temperature. If heat is available, check sensor cable adjustment. If OK, replace sensor. If no heat is available, correct fault in cooling system.
Discharge Temperature Rises on Acceleration
Observe servo vacuum under load. If it drops, an inoperative check valve or a vacuum leak exists. A severe leak will result in an air distribution shift to DEFROST.
Long Periods of Heat, Then Long Periods of Cool or, Long Periods of Cool, Then Long Periods of Heat
Aspirator hose blocked or disconnected. Sensor is not sampling interior air.
Refer to All Function Selector Valve Position Leak Diagnosis, and observe door movement with vacuum input change for attachments.
Thermal Blower Lock Out Switch
The three failures associated with the thermal blower lock out switch are:
^ Short across the two terminals of the harness connector
^ Vacuum leak
^ Coolant leaks
Refer to All Function Selector Valve Positions Leak Diagnosis for vacuum leaks.
Electrical functions can be checked as follows:
Blower Inoperative in FLOOR Position
Engine temperature must be over 43°C (110°F). Unplug electrical connector from thermal blower lock Out switch. Short across the two terminals of the harness connector. If blower comes on, replace thermal blower lock out switch. If blower does not come on, there is an open between the selector switch and the thermal blower lock out switch.
Blower On at All Times in FLOOR Position
If the blower is on with engine coolant under 43°C (110°F), disconnect harness connector from the thermal blower lock out switch. If blower turns off, replace the thermal blower lock out switch. If the blower continues to run, there is a short in the circuit between the selector switch and the thermal blower lock out switch.
Airflow
Refer to Fig. 4 to assist in performing airflow function and Vacuum Motor Application Tests.
Vacuum
Refer to Figs. 4 and 12 through 20 to assist in performing vacuum system and function selector valve tests.
Electrical
Refer to the Lincoln Town Car or Crown Victoria/Grand Marquis Electrical Vacuum Troubleshooting manual for a complete schematic and wire colors.
The wiring diagram and continuity test for Lincoln Town Car is shown in Fig. 21. The wiring diagram and continuity test for Crown Victoria/Grand Marquis is shown in Fig. 22.