A/C Compressor Thermal Fuse - Failure
85jaguar01DATE . . . JANUARY, 1985
NUMBER . . . J85/03
MODEL: XJ6 & XJ-S
SUBJECT: COMPRESSOR THERMAL FUSE
KEY POINTS: Testing Procedure and modification of Ranco Micro Switch on Servo unit.
If problems are being encountered with the persistent failure of the air conditioning compressor thermal fuse, and the test procedures described in Technical Service Bulletin #J85/04 cannot identify any obvious fault, then the following procedure should be carried out.
STEP 1
Follow the directions of the charge station equipment and connect them to the vehicle high and low pressure connections.
CAUTION: Observe all safety precautions as detailed in the Service Manual and the charge station equipment.
Run the engine at normal operating temperature, and select AUTO, 75~, and allow the system to stabilize to ensure that the unit is neither on full cooling nor full heating mode.
Adjust the engine speed to 1000 rev/min and note the readings on the gauges. The readings should be as follows:
The High Pressure gauge should indicate a pressure between 150-225 psi.
The Low Pressure gauge should indicate a pressure not lower than 18 psi when the compressor clutch engages, and not lower than 38 psi when the compressor clutch disengages.
NOTE: Where higher ambient temperatures are encountered, the high pressure reading may be greater than the above.
Ambient temperature is the temperature of the air surrounding the condensor and is taken 2" in front of the condensor.
If the above is satisfactory, proceed to Step 2.
STEP 2
Increase the engine speed to 3000 rev/min and note the reading on the low pressure gauge. The reading should be approximately 10 psi at or just prior to the disengagement of the compressor clutch. If the clutch fails to disengage and the pressure continues to drop to 5 psi or below, then the expansion valve is faulty.
If the pressure remains at 10 psi, and the clutch cycle is correct, select low fan speed. Should the low pressure start to drop, carry out the modification detailed in Step 3.
STEP 3
1. Disconnect the battery.
2. Remove the center console righthand side trim panel to gain access to the air conditioning/heater unit.
3. Remove the plastic retaining plug from the black plastic cover surrounding the servo motor unit.
4. Carefully move aside the shield to gain access to the Ranco override micro switch, A.
5. Disconnect the green/brown (GN) lead and insulate.
6. Reverse procedure 1-4.
NOTE: A significantly high percentage of thermal fuse failures, occurring during high ambients, have been identified as a direct result of selecting low fan speed while the unit is in full cooling mode (65~). Prolonged operation of the system in this condition can result in a significant pressure drop in the low pressure side of the system. Should this be the preferred mode selection while driving, then Step 3 should be implemented immediately.
DATE . . . FEBRUARY, 1985
NUMBER . . . J85/20
MODEL: XJ6 & XJ-S
SUBJECT:
AIR CONDITIONING SERVO UNIT
KEY POINTS:
DELETION OF RANCO
OVERRIDE FUNCTION
Further to Service Bulletin J85/03, reference Step 3, to prevent excessively low pressure being generated in the air conditioning system under certain operating conditions, the servo motor unit Ranco override function has now been deleted. Units to the modified condition were introduced from VINSXJ6 - 411931
XJ-S - 120267