MODEL IDENTIFICATION
| Body Designation (1) | Model |
|---|---|
| "B" Body | Caprice & Roadmaster |
| (1) Body codes are determined by fourth character of VIN code. | |
| (1) | Body codes are determined by fourth character of VIN code. |
BODY CODE DESIGNATIONS
DESCRIPTION & OPERATION
To improve idle quality, Wide Open Throttle (WOT) performance and for system protection, the A/C compressor clutch is controlled by the Engine Control Module (ECM).
A refrigerant pressure sensor is used to indicate high and low side refrigerant pressure to the ECM for controlling cooling fan, A/C compressor clutch and Idle Air Control (IAC) valve. If a fault is detected in refrigerant pressure circuit, A/C compressor clutch will be disabled.
The A/C compressor clutch relay is controlled by the ECM. This allows the ECM to raise idle speed before engaging compressor clutch and to disable compressor clutch during WOT, high engine RPM, high power steering loads and hot engine restarts. ECM also disables compressor clutch if coolant temperature becomes excessive.
TROUBLE SHOOTING
Note. This article contains test charts which are part of General Motors Computerized Engine Controls. Only those charts required to test A/C compressor clutch control are included. Other diagnostic information may be referenced while performing A/C compressor clutch control diagnosis. For complete information on General Motors Computerized Engine Control systems, see appropriate articles in the ENGINE PERFORMANCE section.
Trouble shoot A/C compressor clutch control using appropriate schematic and diagnostic charts. See A/C COMPRESSOR CLUTCH CHARTS. See A/C COMPRESSOR CLUTCH RELAY LOCATION table for A/C compressor clutch relay location.
| Application | Location |
|---|---|
| "B" Body | On right rear corner of engine compartment. |
A/C COMPRESSOR CLUTCH RELAY LOCATION
Scheme 1
SCAN TESTER
A variety of information is transmitted through Data Link Connector (DLC) connector terminal "E" or "M", depending on engine. This data is transmitted at a high frequency which requires a Tech 1 scan tester for interpretation. Several scan testers are available for diagnostic work. Scan testers other than Tech 1 scan tester will function and provide information for diagnostic work; however, some charts will specify a Tech 1 scan tester. Failure to use a Tech 1 scan tester when specified may result in incorrect diagnosis of a system.
CHART C-10, A/C COMPRESSOR CLUTCH DIAGNOSIS (1 OF 2)
The Engine Control Module (ECM) delays A/C compressor clutch engagement after A/C is turned on. This delay allows ECM time to adjust engine RPM before A/C compressor clutch engages. ECM also disengages A/C compressor clutch during Wide Open Throttle (WOT) on 5.7L police models.
When A/C is selected, B+ is applied to pressure cycling switch. If A/C charge is sufficient, pressure cycling switch will be closed, completing circuit to ECM and A/C compressor clutch relay. When A/C request signal is received by ECM, ECM will ground A/C compressor clutch relay circuit No. 459, which allows B+ to be applied to A/C compressor clutch.
Note. Test numbers refer to numbers on diagnostic chart.
1) Checks if ECM is controlling A/C compressor clutch relay.
2) Checks for A/C compressor clutch relay feed circuits shorted to voltage.
3) Manual A/C-heater (C60) system. Automatic A/C-heater (C68) system.
4) Confirms B+ supply to A/C compressor clutch relay.
5) Before replacing any A/C system control components, refer to appropriate AUTOMATIC A/C-HEATER SYSTEMS article in this section.
Diagnostic Aids
If vehicle is equipped with automatic A/C-heater system and climate control DTC 09 is set, refer to appropriate AUTOMATIC A/C-HEATER SYSTEMS article in this section.
ECM will disengage A/C compressor clutch whenever a power steering load is detected. A/C compressor clutch will be disabled during Wide Open Throttle (WOT) on 5.7L police models.
Scheme 2
Scheme 3
CHART C-10, A/C COMPRESSOR CLUTCH DIAGNOSIS (2 OF 2)
Note. Test numbers refer to numbers on diagnostic chart.
1) Manual A/C-heater (C60) system. Automatic A/C-heater (C68) system.
2) Confirms B+ to A/C control relay.
3) Jumpering harness connector will determine if high pressure cut-out switch is open.
