A/c Compressor Clutch Controls — Buick LeSabre VII (1992-1999)

MODEL IDENTIFICATION

Body Designation (1)	Model
"C" Body	Ninety Eight & Park Avenue
"H" Body	Bonneville, Eighty Eight & LeSabre
(1) Body codes determined by fourth character of VIN code.

(1)	Body codes determined by fourth character of VIN code.

BODY CODE DESIGNATIONS

DESCRIPTION & OPERATION

To improve idle quality and Wide Open Throttle (WOT) performance, and for system protection, the A/C compressor clutch is controlled by the Powertrain Control Module (PCM).

A refrigerant pressure sensor is used to indicate high and low side refrigerant pressure to the PCM 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 PCM. This allows the PCM to raise idle speed before engaging compressor clutch, and disable compressor clutch during WOT, high engine RPM, high power steering loads and hot engine restarts. PCM 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 the appropriate G-TESTS W/CODES article in the ENGINE PERFORMANCE section.

TESTS W/CODES - Park Avenue, Ninety Eight

TESTS W/CODES - LeSabre, Eighty Eight, Bonneville

Trouble shoot A/C compressor clutch control using appropriate schematic and diagnostic charts. See TROUBLE SHOOTING CHART DIRECTORY. See A/C COMPRESSOR CLUTCH RELAY LOCATION table for A/C compressor clutch relay location.

RELAY LOCATION

Application	Location
"C" & "H" Bodies	Center Rear Of Engine Compartment, In Fuse/Relay Block

A/C COMPRESSOR CLUTCH RELAY LOCATION

TROUBLE SHOOTING CHART DIRECTORY

Application		See Figure
3.8L VIN K, L & 1
Manual A/C-Heater		Figs. (Scheme 1) - (Scheme 4)
Automatic A/C-Heater		Figs. (Scheme 5) - (Scheme 8)

A/C COMPRESSOR CLUTCH CHART INDEX

SCAN TESTER

A variety of information is transmitted through Data Link Connector (DLC) 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 CIRCUIT DIAGNOSIS 3.8L - VIN K, L & 1 - MANUAL A/C-HEATER

Powertrain Control Module (PCM) delays A/C compressor clutch engagement momentarily after A/C is turned on. This delay allows Idle Air Control (IAC) motor to adjust engine RPM before A/C compressor clutch engages. PCM also disengages A/C compressor clutch during Wide Open Throttle (WOT). A/C compressor clutch is energized when PCM grounds circuit No. 459. PCM may engage A/C compressor clutch during engine cranking.

Scheme 1

Scheme 1: CHART C-10 - A/C COMPRESSOR CLUTCH CIRCUIT DIAGNOSIS 3.8L - VIN K, L & 1 - MANUAL A/C-HEATER

Note. Test numbers refer to numbers on diagnostic chart. (Scheme 2)

1) A/C compressor clutch should not be engaged with engine running if an A/C mode is not selected at control head.

2) A/C compressor clutch should apply if conditions under NOTICE at top of chart are met.

3) Checks for an A/C request signal from control head to pressure cycling switch.

Scheme 2

Note. Test numbers refer to numbers on diagnostic chart. (Scheme 3)

1) Checks for ignition voltage on circuit No. 639 and PCM control of ground circuit No. 459 to A/C compressor clutch relay coil.

2) Checks for ignition voltage on circuit No. 639 to A/C compressor clutch relay contacts.

3) Determines whether A/C compressor clutch relay, compressor clutch coil or circuitry is faulty.

Scheme 3

Note. Test numbers refer to numbers on diagnostic chart. (Scheme 4)

1) Determines if PCM is turning A/C compressor clutch relay on due to a false A/C request signal.

2) Determines whether problem is in A/C control head and circuits No. 604 and 762 to pressure cycling switch, or circuit No. 204 and PCM.

3) Checks for circuit No. 59 shorted to battery voltage or a faulty A/C compressor clutch.

4) Determines if A/C compressor clutch relay is faulty or A/C compressor clutch relay control circuit No. 459 is grounded at all times.

Scheme 4

CHART C-10 - A/C COMPRESSOR CLUTCH CIRCUIT DIAGNOSIS 3.8L - VIN K, L & 1 - AUTOMATIC A/C-HEATER

Scheme 5

Scheme 5: CHART C-10 - A/C COMPRESSOR CLUTCH CIRCUIT DIAGNOSIS 3.8L - VIN K, L & 1 - AUTOMATIC A/C-HEATER

Note. Test numbers refer to numbers on diagnostic chart. (Scheme 6)

1) Determines whether or not PCM recognizes the A/C request signal.

2) Checks for an open high pressure cut-out switch.

3) Ensures that A/C-heater control programmer is supplying the A/C request signal.

Scheme 6

Note. Test numbers refer to numbers on diagnostic chart. (Scheme 7)

1) Determines whether A/C relay can be controlled by PCM.

2) Checks for ignition voltage to A/C relay contacts.

3) Determines whether problem is caused by A/C relay, relay connections, compressor clutch or compressor clutch circuit is at fault.

Scheme 7

Note. Test numbers refer to numbers on diagnostic chart. (Scheme 8)