Part 1 of 2

A/C Compressor Clutch Circuit Diagram:

CIRCUIT DESCRIPTON
The A/C clutch relay gets battery power when the ignition is turned and energized when the PCM completes the circuit to ground. When energized, the relay turns the A/C compressor clutch "ON", engaging the compressor. The A/C pressure sensor signal is used to determine high and low pressure in the system and for cooling fan control. When the A/C is turned on, the PCM delays the clutch engagement of the A/C compressor for a fraction iof a second, allowing the IAC valve time to increase air flow and compensate for the added load. The PCM also turns the relay "OFF", disengaging the A/C clutch, under the following conditions:

^ Wide open throttle
^ High power steering pressure is present at idle
^ When the engine is overheating
^ When the A/C system pressures are not within a specified range.
^ Engine speed excedes 6,000 rpm.
^ Code 66 present

TEST DESCRIPTION

Chart C-10, A/C Compressor Clutch Control Circuit Diagnosis (1 Of 2):

Numbers below refer to circled numbers on diagnostic chart.

1. The PCM will only energize the compressor clutch relay when the engine is running. If clutch is engaged, there is a short to ground in circuit 459, short to battery power circuit 59, or PCM is faullty.
2. Determines if PCM is receiving the A/C request signal from the A/C control panel (circuit 66). Signal should be present when the selector is in an A/C or defrost position.
3. If the PCM is receiving a high pressure indication from the Power Steering Pressure Switch, the A/C clutch will be disengaged.

DIAGNOSTIC AIDS
If the complaint is insufficient cooling, the problem may be an inoperative engine cooling fan. Chart C-12 Coolant Fan Control Circuit If cooling fans operate properly, problem may be A/C pressures outside of range, or faulty pressure transducer indicating pressure out of range (43 - 428 psi). Monitor A/C pressure with "SCAN" tool and compare to actual readings with A/C manifold/gauges. "SCAN" readings should be within 20 psi of actual pressure. If not see Code 66 diagnostic chart, or replace pressure transducer.