HVAC System Compressor Clutch Controls Cadillac Catera I

A/C COMPRESSOR CLUTCH CONTROLS

When A/C button on A/C-heater control panel is pressed, an A/C request signal is sent through the refrigerant pressure switch and Engine Control Module (ECM) to the coil of A/C clutch relay (K60). The A/C clutch relay is located at left front of engine compartment, in ECM housing. This enables A/C clutch relay to energize, allowing ignition voltage to energize compressor clutch coil and fan control relay (K87).

When fan control relay energizes, battery voltage is supplied to auxiliary cooling fan No. 1 and through the normally open contacts of fan control relay (K52), to auxiliary cooling fan No. 2. If coolant temperature reaches 248°F (120°C), secondary temperature switch contacts will open and the compressor clutch coil is disengaged, causing A/C system to turn off. Secondary temperature switch will not allow A/C system to turn back on until coolant temperature has dropped to 239°F (115°C) or less.

Compressor clutch coil can also be turned off by refrigerant pressure switches (low pressure switch or high pressure switch). Low pressure switch will turn compressor clutch off as soon as refrigerant pressure falls to about 26 psi (1.8 kg/cm 2 ). This is done by opening the low pressure switch contacts and not allowing battery voltage to pass through A/C clutch relay (K60) to compressor clutch coil. Low pressure switch activates the compressor clutch when refrigerant pressure increases to about 36.3 psi (2.6 kg/cm 2 ).

High pressure switch will turn compressor clutch off as soon as refrigerant pressure exceeds about 435 psi (30.6 kg/cm 2 ). This is done by opening the high pressure switch contacts in refrigerant pressure switch and not allowing battery voltage to pass through A/C clutch relay (K60) to compressor clutch. High pressure switch activates compressor clutch when refrigerant pressure drops less than about 290 psi (19.3 kg/cm 2 ).

When refrigerant pressure exceeds about 159.4 psi (11.2 kg/cm 2 ),A/C control switch contacts will close and engine idle speed will increase to compensate for RPM drop that occurs when A/C system is switched on. A/C control switch is installed in high pressure line, between A/C compressor and condenser. When refrigerant pressure drops less than about 130. 5 psi (9.2 kg/cm 2 ), A/C control switch contacts will close and allow engine idle speed to return to normal.

A/C CLUTCH CIRCUIT DIAGNOSIS

To help save diagnostic time, ALWAYS check for blown fuses or fusible links before proceeding with any testing. If fuses are blown, locate and repair short circuit before replacing fuses.

Ensure all related relay and wire harness connections are clean and tight. Repair as necessary. See WIRING DIAGRAMS .

Note. Catera is equipped with an anti-theft system. ECM must be reprogrammed when replaced. See ANTI-THEFT SYSTEM article in ACCESSORIES & ELECTRICAL for reprogramming procedures.

Description

The following diagnostic procedure tests operation of A/C request circuit, A/C load signal circuit and compressor clutch control circuit. For proper A/C system operation, A/C request circuit monitors selected A/C mode, A/C system pressure and throttle position. When A/C mode is selected with A/C system pressure and throttle angle at a predetermined value, Engine Control Module (ECM) energizes A/C clutch relay through A/C clutch relay control circuit.

During A/C system operation with excessively high A/C system pressures, A/C load switch closes, sending a battery voltage signal to ECM on A/C load signal circuit. ECM will increase idle speed about 50 RPM to compensate for compressor load. ECM de-energizes A/C clutch relay during wide open throttle, when engine coolant temperature or A/C system pressure exceeds a predetermined threshold, or when a non-A/C mode is selected.

A/C Request Circuit Diagnosis

1. If On-Board Diagnostic (OBD) System Check has not been performed, see OBD SYSTEM CHECK in TESTS W/CODES article in ENGINE PERFORMANCE. If OBD SYSTEM CHECK has been performed, go to next step.
2. Start engine and let idle. While observing A/C REQUEST on scan tool display, turn A/C on and off. If A/C REQUEST toggles between YES and NO, A/C request circuit is okay at this time. See DIAGNOSTIC AIDS. If A/C REQUEST does not toggle between YES and NO, go to next step.
3. If A/C REQUEST is always YES, go to next step. If A/C REQUEST is always NO, go to step 5).
4. Disconnect A/C pressure switch harness connector. If A/C REQUEST changes to NO, diagnose A/C-heater system. See procedures in «A/C-HEATER SYSTEM»(/cadillac/catera/i-1996-2001/remont/automatic-hvac-system/#hvac-system) article. If A/C REQUEST remains as YES, go to step 6).
5. Turn ignition on, engine off. Disconnect A/C pressure switch harness connector. Using a fused jumper wire connected to battery voltage, probe terminal No. 1 (A/C request circuit) at A/C pressure switch harness connector. If A/C REQUEST changes to YES, diagnose A/C-heater system. See «A/C-HEATER SYSTEM»(/cadillac/catera/i-1996-2001/remont/automatic-hvac-system/#hvac-system) article. If A/C REQUEST remains as NO, go to next step.
6. Turn ignition off. Disconnect ECM harness connectors. Turn ignition on, engine off. Using a DVOM, check A/C request circuit (Black/White wire) between ECM and A/C pressure switch for an open, short to power or short to ground. Repair as necessary. Go to step 9). If no problem is found, go to next step.
7. Check for poor harness connections at ECM. Repair as necessary. Go to step 9). If no problem is found, go to next step.
8. Replace ECM. Go to next step.
9. Start engine and let idle. While observing A/C REQUEST on scan tool display, turn A/C on and off. If A/C REQUEST toggles between YES and NO, A/C request circuit is okay. If A/C REQUEST does not toggle between YES and NO, go to step 2).

A/C Load Signal Circuit Diagnosis

1. If On-Board Diagnostic (OBD) System Check has not been performed, see OBD SYSTEM CHECK in TESTS W/CODES article in ENGINE PERFORMANCE. If OBD SYSTEM CHECK has been performed, go to next step.
2. Start engine and let idle. With A/C off, observe A/C LOAD SIGNAL on scan tool display. If A/C LOAD SIGNAL indicates HEAVY, go to next step. If A/C LOAD SIGNAL does not indicate HEAVY, go to step 4).
3. Disconnect A/C load switch harness connector. If A/C LOAD SIGNAL changes to NORMAL, go to step 10). If A/C LOAD SIGNAL does not change to NORMAL, go to step 8).
4. Turn ignition on, engine off. Disconnect A/C load switch harness connector. Using a test light connected to ground, probe ignition feed circuit (Brown wire) in A/C load switch harness connector. If test light illuminates, go to next step. If test light does not illuminate, go to step 9).
5. Using a fused jumper wire, jumper A/C load switch harness connector terminals together. Observe scan tool. If A/C LOAD SIGNAL changes to HEAVY, go to next step. If A/C LOAD SIGNAL does not change to HEAVY, go to step 8).
6. Check for poor terminal connections at A/C load switch harness connector. Repair as necessary. Go to step 13). If no problem is found, go to next step.
7. Install A/C manifold gauge set. Start engine and turn A/C on. Increase engine speed to 2000 RPM. Observe A/C LOAD SIGNAL on scan tool and high-side pressure on gauge. If A/C LOAD SIGNAL changes to HEAVY when high-side pressure reaches 174 psi (12.2 kg/cm 2 ), A/C load signal circuit is okay at this time. See DIAGNOSTIC AIDS. If A/C LOAD SIGNAL does not change to HEAVY, go to step 10).
8. Turn ignition off. Disconnect ECM harness connectors. Turn ignition on, engine off. Using a DVOM, check A/C load signal circuit (Black/Blue wire) between ECM and A/C load switch for an open, short to ground or short to power. Repair as necessary. Go to step 13). If no problem is found, go to step 11).
9. Repair open or high resistance in ignition feed circuit (Brown wire) to A/C load switch. Go to step 13).
10. Replace A/C load switch. Go to step 13).
11. Check for poor terminal connections at ECM. Repair as necessary. Go to step 13). If no problem is found go to next step.
12. Replace ECM. Go to next step.
13. Start engine and let idle. Turn A/C off. Observe A/C LOAD SIGNAL on scan tool display. If A/C LOAD SIGNAL indicates HEAVY, go to step 2). If A/C LOAD SIGNAL does not indicate HEAVY, go to next step.
14. Disconnect A/C load switch harness connector. Observe scan tool display. If A/C LOAD SIGNAL changes to NORMAL, go to next step. If A/C LOAD SIGNAL does not change to NORMAL, go to step 2).
15. Using a fused jumper wire, jumper A/C load switch harness connector terminals together. Observe scan tool display. If A/C LOAD SIGNAL changes to HEAVY, A/C load signal circuit is okay. If A/C LOAD SIGNAL does not change to HEAVY, go to step 2).

A/C Compressor Control Circuit Diagnosis

1. If On-Board Diagnostic (OBD) System Check has not been performed, see OBD SYSTEM CHECK in TESTS W/CODES article in ENGINE PERFORMANCE. If OBD SYSTEM CHECK has been performed, go to next step.
2. Turn ignition on, engine off. Using scan tool, command A/C clutch relay on and off. If A/C clutch relay turns on and off "clicks", go to next step. If A/C clutch relay does not turn on and off, go to step 5).
3. Turn ignition off. Disconnect ECM harness connectors. Turn ignition on, engine off. Using a DVOM on 10-amp scale, measure current from A/C clutch relay control circuit (Brown/Purple wire) at ECM harness connector to ground for 2 minutes. If current draw is 0.1-0.75 amp, compressor control circuit is okay. See DIAGNOSTIC AIDS. If current draw is not as specified, go to next step.
4. Turn ignition off. Disconnect A/C clutch relay. Using a DVOM, measure resistance between ground and A/C clutch relay control circuit (Brown/Purple wire) at ECM harness connector. If resistance is infinite, go to step 11). If resistance is not as specified, go to step 9).
5. Turn ignition off. Disconnect A/C clutch relay. Connect a test light between Brown wire and Brown/Purple wire at A/C clutch relay harness connector. Turn ignition on. Using scan tool, command A/C clutch relay on and off. If test light flashes on and off, go to step 8). If test light does not flash on and off, go to next step.
6. Using a test light connected to ground, probe ignition feed circuit (Red wire) at A/C clutch relay harness connector. If test light illuminates, go to next step. If test light does not illuminate, go to step 10).
7. Turn ignition off. Reconnect A/C clutch relay. Disconnect ECM harness connectors. Turn ignition on, engine off. Using a fused jumper wire connected to ground, probe A/C clutch relay control circuit (Brown/Purple wire) at ECM harness connector. If A/C clutch relay operates "clicks", go to step 12). If A/C clutch relay does not operate, go to step 9).
8. Check for poor connections at A/C clutch relay. Repair as necessary. Go to step 14). If no problem is found, go to step 11).
9. Repair A/C clutch relay control circuit (Brown/Purple wire). Go to step 14).
10. Repair ignition feed circuit (Red wire) to A/C clutch relay. Go to step 14).
11. Replace A/C clutch relay. Go to step 14).
12. Check for poor ECM harness connections. Repair as necessary. go to step 14). If no problem is found, go to next step.
13. Replace ECM. Go to next step.
14. Turn ignition on, engine off. Using scan tool, command A/C clutch relay on and off. If A/C clutch relay turns on and off "clicks", compressor control circuit is okay. If A/C clutch relay does not turn on and off, go to step 2).

Diagnostic Aids

A/C pressure switch only closes when refrigerant high-side pressure reaches about 174 psi (12.2 kg/cm 2 ). Proper switch operation cannot be verified if ambient temperature will not allow proper system pressures to be achieved.

An intermittent condition may be caused by corrosion, misrouted wiring harness, rubbed through wire insulation or a wire broken inside insulation.

A/C Compressor Clutch Control Circuit Wiring Diagram. Scheme 1

See also:
• A/C-HEATER SYSTEM
• WIRING DIAGRAMS