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pressure cut-off switch located on the expansion valve. If voltage is not detected, refer to:

²Group 8W, Wiring Diagrams.

²The appropriate Powertrain Diagnostic Procedures Manual for diagnostic information.

If voltage is detected at the cut-off switch, reconnect switch. Then check for battery voltage between the compressor clutch connector terminals.

If voltage is detected, perform A/C Clutch Coil Tests.

CLUTCH COIL TESTS

(1)Verify battery state of charge. (Test indicator in battery should be green).

(2)Connect an ammeter (0-10 ampere scale) in series with the clutch coil terminal. Use a volt meter (0-20 volt scale) with clip leads measuring voltage across the battery and A/C clutch.

(3)With A/C control in A/C mode and blower at low speed, start the engine and run at normal idle.

(4)The A/C clutch should engage immediately and the clutch voltage should be within two volts of the battery voltage. If the A/C clutch does not engage, test the fusible link.

(5)The A/C clutch coil is acceptable if the current draw is 2.0 to 3.7 amperes at 11.5-12.5 volts at clutch coil. This is with the work area temperature at 21°C (70°F). If voltage is more than 12.5 volts, add electrical loads by turning on electrical accessories until voltage reads below 12.5 volts.

If coil current reads zero, the coil is open and should be replaced. If the ammeter reading is 4 amperes or more, the coil is shorted and should be replaced. If the coil voltage is not within two volts of the battery voltage, test clutch coil feed circuit for excessive voltage drop.

LOW-PRESSURE CUT-OFF SWITCH DIAGNOSIS

The Low Pressure Cut-Off (LPCO) Switch (Fig. 3) monitors the refrigerant gas pressure on the suction side of the system. The LPCO is located on the expansion valve, and the expansion valve is silver in color when a fixed displacement compressor is used. The LPCO turns off voltage to the compressor clutch coil when refrigerant gas pressure drops to levels that could damage the compressor. The LPCO is a sealed factory calibrated unit. It must be replaced if defective.

LPCO SWITCH TEST

The work area must not be below 10°C (50°F) to test the compressor clutch circuit.

(1)With gear selector in park or neutral and park brake set, start engine and allow to idle.

(2)Raise hood and disconnect LPCO switch connector boot.

(3)Using a suitable jumper wire, jump across the terminals inside wire connector boot.

Fig. 3 Low Pressure Cut-Off Switch

(4)If the compressor clutch does not engage, the cycling clutch switch, wiring, relay, or fuse can be defective. Refer to Group 8W, Wiring Diagrams.

(5)If clutch engages, connect manifold gauge set. Read low pressure gauge. At pressure above 97 kPa (14 psi) and above, LPCO switch will complete the clutch circuit. If the low pressure gauge reads below 172 kPa (25 psi), the system is low on refrigerant charge or empty due to a leak. Refer to Testing For Refrigerant Leaks in the Refrigerant Service Procedures section.

(6)Install connector boot on switch and repeat step number 3. If the clutch does not engage, replace the LPCO switch.

THERMAL LIMITER SWITCHÐMODEL TR105 COMPRESSOR

The Thermal Limiter Switch (Fig. 4) is bolted to the side of the compressor case. It measures compressor surface temperature and is used as a safety device to cut battery voltage to the compressor clutch coil. This is performed if compressor case temperature is excessive.

This switch isNOT USED to cycle the clutch coil. After the compressor has cooled to normal operating temperature, the switch will reset.

TESTING THERMAL LIMITER SWITCH

The switch can remain bolted to the compressor for testing.

(1)Disconnect the wiring connectors from the thermal limiter switch.

(2)Using an ohmmeter, check for continuity between the two wiring leads. If continuity is not detected, replace switch. Also check for possible compressor overheating.

²Switch cut-out (no continuity) occurs at 125°C 63°C (255°F 637°F).

²Switch cuts back in (continuity) at 110°C 66°C (230°F 642°F).

Fig. 4 Thermal Limiter Switch

To replace switch, refer to Thermal Limiter Switch.

FIN-SENSING CYCLING CLUTCH SWITCH DIAGNOSIS

The Fin-Sensing Cycling Clutch Switch (FCCS) (Fig. 5) is located in the heater-A/C unit housing near the blower motor and placed in the evaporator fins. The FCCS prevents evaporator condensate freeze-up. This is done by cycling the compressor clutch OFF when evaporator temperature drops below freeze point. It cycles ON when the evaporator temperature rises above freeze point. The FCCS uses a thermistor probe in a capillary tube inserted between the evaporator fins in the heater-A/C unit housing. If the compressor clutch does not cycle, and all other clutch circuit components test correct, test the switch. Refer to Fin-Sensing Cycling Clutch Switch Tests.

Fig. 5 Fin-sensing Cycling Clutch Switch

Fig. 6 Fin-sensing Cycling Clutch Switch Harness

Connector

(3) If compressor clutch engages, test for continuity from terminal pin #1 to pin #3 of the switch lead connector. Continuity should be detected. If not, replace the Fin-sensing Cycling Clutch Switch.

FIXED DISPLACEMENT COMPRESSOR REFRIGERANT SYSTEM

Refer to the Refrigerant System Diagnosis chart in this section.

SILVER EXPANSION VALVE TEST

Expansion valve tests should be performed after compressor tests.

Review Safety Precautions and Warnings in the General Information section of this Group. The work area and vehicle must be 21°C to 27°C (70°F to 85°F) when testing expansion valve. To test the expansion valve:

(1)Connect a charging station or manifold gauge set to the refrigerant system service ports. Verify the refrigerant charge level using the sight glass method.

(2)Disconnect and plug the vacuum line at the water control valve.

Fig. 7 Low Pressure Cut-Off Switch

(4)Close all doors, windows and vents to the passenger compartment.

(5)Set heater-A/C control to A/C, full heat, FLOOR, and high blower.

(6)Start the engine and hold the idle speed (1000 rpm). After the engine has reached running temperature, allow the passenger compartment to heat up. This will create the need for maximum refrigerant flow into the evaporator.

(7)If the refrigerant charge is sufficient, discharge (high pressure) gauge should read 965 to 1655 kPa (140 to 240 psi). Suction (low pressure) gauge should read 140 kPa to 207 kpa (20 psi to 30 psi). If system cannot achieve proper pressure readings, replace the expansion valve. If pressure is correct, proceed with test.

WARNING: PROTECT SKIN AND EYES FROM CONTACTING CO2 PERSONAL INJURY CAN RESULT.

(8)If suction side low pressure is within specified range, freeze the expansion valve control head (Fig. 8) for 30 seconds. Use a super cold substance (liquid

CO2). Do not spray R-12 Refrigerant on the expansion valve for this test. Suction side low pressure should drop to -50 kPa (-15 in. Hg) If not, replace expansion valve.

(9)Allow expansion valve to thaw. The low pressure gauge reading should stabilize at 140 kPa to 240 kPa (20 psi to 30 psi). If not, replace expansion valve.

Fig. 8 Expansion Valve

When expansion valve test is complete, test A/C overall performance. Refer to the Heater and A/C Performance Test in this section. Remove all test equipment before returning vehicle to use.

HIGH PRESSURE RELIEF VALVE (HPR) DIAGNOSIS

The HPR valve prevents damage to the air-condi- tioning system if excessive pressure develops. Excessive pressure may be caused by condenser air flow blockage, refrigerant overcharge, or air and moisture in the system.

(HPR) VALVE LOCATION

The HPR Valve is located on the discharge line at the A/C compressor (Fig. 9).

Fig. 9 High Pressure Relief ValveÐ Typical

The high pressure relief valve vents only a small amount of refrigerant necessary to reduce system pressure and then reseats itself. The majority of the refrigerant is conserved in the system. The valve is calibrated to vent at a pressure of 3100 to 4140 Kpa (450 to 600 psi). If a valve has vented a small amount of refrigerant, it does not necessarily mean the valve is defective.

For (HPR) valve replacement, refer to Fixed Displacement Compressor Service Procedures section.