Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
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HOMESERVICE MANUALSJAGUAR1986VANDEN PLAS L6-4.2LREPAIR AND DIAGNOSISHEATING AND AIR CONDITIONINGTESTING AND INSPECTIONCOMPONENT TESTS AND GENERAL DIAGNOSTICSA/C SYSTEM FUNCTIONAL TESTCONTROL SYSTEM
1986 Jaguar Vanden Plas L6-4.2L
Control System
1986 Jaguar Vanden Plas L6-4.2LSECTION Control System
A/C System Functional Test - Control System
1. With engine cold, turn TEMPERATURE SELECTOR to 85 and MODE CONTROL to AUTO.
2. Start engine and run at 1.000 rpm. Servo motor should be heard.
3. Blowers should not operate until engine coolant temperature reaches 103° F (40° C).
4. At 103° F (40° C), blowers should come on at MED 1 (2nd) speed. Check for correct speed by selecting LO at MODE CONTROL. Fans should drop to low (1st) speed. Place control back to AUTO. Compressor clutch should be energized.
5. Air from outlets will gradually increase in temperature as engine coolant temperature increases.
6. With engine warm, and ambient air temperature at 75 - 80° F, turn TEMPERATURE SELECTOR to 65. Unit should go through the following sequence in about 20 seconds.
a. Blower speed drops to low.
b. Incoming temperature will decrease.
c. Center flap should open after about 10 seconds.
d. About 1 second later, blower speed shifts to MED 1 (2nd) speed.
e. Another second later, blower speed shifts to MED 2 (3rd) speed.
f. Another second later, blower speed shifts to HIGH (4th) speed, fresh air vents close and recirculation flaps open.
7. Turn MODE CONTROL to LO which should cause blower speed to drop. Return MODE CONTROL to AUTO.
NOTE: It may be hard to hear fan speed change.
8. Within ten minutes, depending upon ambient conditions, the unit should shift off recirculation and blowers will drop to one of the intermediate speeds. (This test should be carried out on a road test to get faster thermistor response).
9. Turn MODE CONTROL to DEFROST. Center dash flap should close and defrost vent open. Air to footwells should cut off.
10. Blowers should shift to HIGH and hot air should flow from defrost vents. Check for blowers for vibration.
11. Check operation of dash outer vents. Rotation of thumb wheel should cut off air flow from vent.
12. Set MODE CONTROL to AUTO. Set temperature selector to 75 and wait for unit to settle.
13. Blowers should now be on low speed, depending on ambient temperature.
14. Turn MODE CONTROL to HIGH. High speed should now engage.
1. With engine cold, turn TEMPERATURE SELECTOR to 85 and MODE CONTROL to AUTO.
2. Start engine and run at 1.000 rpm. Servo motor should be heard.
3. Blowers should not operate until engine coolant temperature reaches 103° F (40° C).
4. At 103° F (40° C), blowers should come on at MED 1 (2nd) speed. Check for correct speed by selecting LO at MODE CONTROL. Fans should drop to low (1st) speed. Place control back to AUTO. Compressor clutch should be energized.
5. Air from outlets will gradually increase in temperature as engine coolant temperature increases.
6. With engine warm, and ambient air temperature at 75 - 80° F, turn TEMPERATURE SELECTOR to 65. Unit should go through the following sequence in about 20 seconds.
a. Blower speed drops to low.
b. Incoming temperature will decrease.
c. Center flap should open after about 10 seconds.
d. About 1 second later, blower speed shifts to MED 1 (2nd) speed.
e. Another second later, blower speed shifts to MED 2 (3rd) speed.
f. Another second later, blower speed shifts to HIGH (4th) speed, fresh air vents close and recirculation flaps open.
7. Turn MODE CONTROL to LO which should cause blower speed to drop. Return MODE CONTROL to AUTO.
NOTE: It may be hard to hear fan speed change.
8. Within ten minutes, depending upon ambient conditions, the unit should shift off recirculation and blowers will drop to one of the intermediate speeds. (This test should be carried out on a road test to get faster thermistor response).
9. Turn MODE CONTROL to DEFROST. Center dash flap should close and defrost vent open. Air to footwells should cut off.
10. Blowers should shift to HIGH and hot air should flow from defrost vents. Check for blowers for vibration.
11. Check operation of dash outer vents. Rotation of thumb wheel should cut off air flow from vent.
12. Set MODE CONTROL to AUTO. Set temperature selector to 75 and wait for unit to settle.
13. Blowers should now be on low speed, depending on ambient temperature.
14. Turn MODE CONTROL to HIGH. High speed should now engage.
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When to See a Mechanic
Stop DIY work and contact a certified mechanic immediately if any of the following apply:
- • You smell fuel, burning insulation, or see smoke.
- • Brakes feel soft, pull hard to one side, or make grinding noises.
- • The engine overheats, stalls repeatedly, or misfires under load.
- • You are missing required tools, torque specs, or safe lifting equipment.
- • You are not confident in the next step or safety outcome.