Except Catera
To provide improved idle quality, improved Wide Open Throttle (WOT) performance and A/C system protection, the compressor clutch is controlled by PCM.
For proper control of cooling fans, compressor clutch, and Idle Air Control (IAC) valve, a refrigerant pressure sensor is used. The PCM uses signals provided by sensor to monitor high and low side refrigerant pressures. If PCM detects a fault in refrigerant pressure circuit, compressor clutch will be disabled.
The A/C clutch relay is controlled by PCM. This allows PCM to raise idle speed before engaging compressor clutch, or disable compressor clutch during WOT, high engine RPM, high power steering loads, and hot engine restarts. The PCM also disables compressor clutch if coolant temperature becomes excessive.
Note. This article ONLY contains those testing procedures required to test A/C compressor clutch control circuit. Other diagnostic information may be referenced while performing A/C compressor clutch control diagnosis. For additional information, see appropriate SELF-DIAGNOSTICS article in ENGINE PERFORMANCE.
Catera
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 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 435 psi (30.6 kg/cm 2 ). This is done by opening 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 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 ), the A/C control switch contacts will close and allow engine idle speed to return to normal.
| Application | Location |
|---|---|
| C Body | Right Front Of Engine Compartment, In Fuse/Relay Block |
| E & K Bodies | In Underhood Fuse/Relay Block |
| F Body | In Underhood Electrical Center, On Left Inner Fender Panel |
| G Body | In Underhood Relay Center, At Right Front Of Engine Compartment |
| H Body | Center Rear Of Engine Compartment, Below Right Fuse Block |
| J Body | In Underhood Fuse/Relay Block, At Left Front Of Engine Compartment |
| N Body | At Right Rear Of Engine Compartment |
| V Body | Left Front of Engine Compartment, In ECM Housing |
| W Body | In Underhood Electrical Center, At Right Front Of Engine Compartment |
| Y Body | In Underhood Electrical Center, In Front Of Battery |
A/C CLUTCH RELAY LOCATION (CARS)
FWD Vans
To provide improved idle quality, maintain Wide Open Throttle (WOT) performance and provide A/C system protection, compressor clutch is controlled by PCM.
The A/C clutch relay is controlled by PCM according to information received from A/C pressure sensor and various other sensors. This allows the PCM to raise idle speed before engaging compressor clutch. PCM will disable compressor clutch during WOT, when refrigerant pressure is incorrect or if coolant temperature exceeds a predetermined value. The PCM inhibits compressor clutch operation when engine speed is greater than 4500 RPM for 5 seconds, or when throttle angle exceeds 90 percent.
Note. Astro and Safari are equipped with a Vehicle Control Module (VCM). Substitute PCM with VCM in the following system description as necessary.
RWD Trucks & Vans
The A/C clutch relay is controlled by PCM. The PCM improves idle quality by delaying compressor clutch engagement until idle speed is increased, or disengages compressor clutch when idle speed is too low. Compressor clutch is cycled by PCM. The PCM smooths cycling of compressor clutch by adding fuel the instant compressor clutch is applied.
| Application (1) | Location |
|---|---|
| C & K Series | In Underhood Fuse/Relay Center, Left Rear Of Engine Compartment |
| S & T Series | In Underhood Fuse Block |
| G Series | In Underhood Fuse/Relay Center, Left Front Of Engine Compartment |
| Sierra & Silverado | In Underhood Bussed Electrical Center |
| L & M Series | In Underhood Fuse/Relay Center, Left Side Of Engine Compartment |
| U Body | In Underhood Accessory Wiring Junction Block |
| (1) "P" series A/C clutch relay location will vary with coach builder. See coach manufacturer's information for location. | |
| (1) | "P" series A/C clutch relay location will vary with coach builder. See coach manufacturer's information for location. |
A/C CLUTCH RELAY LOCATION (LIGHT TRUCKS & VANS)
2.4L: ALERO, GRAND AM & MALIBU
Note. Body Function Controller (BFC) may also be referred to as a Body Control Module (BCM).
3.0L: CATERA
Note. Catera is equipped with an anti-theft system. ECM must be programmed when replaced. See appropriate ANTI-THEFT SYSTEMS article in ACCESSORIES & EQUIPMENT or COMPUTER RELEARN PROCEDURES article in GENERAL INFORMATION in ENGINE PERFORMANCE.
3.4L: ALERO & GRAND AM
Note. Body Function Controller (BFC) may also be referred to as a Body Control Module (BCM).
4.6L: DEVILLE & ELDORADO
Note. Since many DTCs cause PCM to disable A/C compressor clutch operation, any DTCs stored in memory must be repaired and cleared before proceeding. See appropriate SELF-DIAGNOSTICS article in ENGINE PERFORMANCE.
4.6L: SEVILLE
Note. Since many DTCs cause PCM to disable compressor clutch operation, any DTCs stored in memory must be repaired and cleared before proceeding. See appropriate SELF-DIAGNOSTICS article in ENGINE PERFORMANCE.
5.7L: CAMARO, CORVETTE & FIREBIRD
Note. The following diagnostic procedures apply to manual A/C-heater systems only. For diagnosis of automatic A/C-heater systems, see appropriate AUTOMATIC A/C-HEATER SYSTEMS - CORVETTE article.
4.3L: "C", "G", "K", "L", "M", "P", "S" & "T" SERIES (INCLUDING SIERRA & SILVERADO), 5.0L: "C", "G" & "K" SERIES OR 5.7L, 6.5L & 7.4L: "C", "G", "K" & "P" SERIES
Note. The 6.5L diesel engines are equipped with a Powertrain Control Module (PCM). Substitute VCM with PCM in the following test when diagnosing vehicles equipped with diesel engines.
4.8L, 5.3L & 6.0L: SIERRA & SILVERADO
Note. The following diagnostic procedure is only for PCM controlled A/C circuits. For VCM controlled A/C circuits, see 4.3L: "C", "G", "K", "L", "M", "P", "S" & "T" SERIES (INCLUDING SIERRA & SILVERADO) diagnosis.