Circuit Description
The PCM controls the operation of the A/C clutch through the A/C clutch relay. When the operator selects an A/C mode on the HVAC control module, the HVAC module sends a B+ signal (A/C request) through the A/C high pressure switch to the PCM. The A/C high pressure switch is normally closed unless a high pressure condition exists. This signal is displayed on the scan tool as A/C REQUEST. The PCM supplies a B+ signal to the A/C compressor cycling switch (which is normally closed when A/C pressure is between 18-49 psi), to ground. When these two inputs are received by the PCM, the PCM then supplies a ground on the A/C relay control circuit closing the relay contacts.
The PCM controlled HVAC system consist of the following:
| • | The A/C High Pressure Cutout Switch |
| • | The A/C Compressor Cycling Switch |
| • | The A/C Compressor Clutch Relay |
| • | The PCM |
The PCM will engage the A/C clutch any time the engine speed is below 5000 RPM and the A/C is requested unless any of the following conditions exist:
| • | Throttle angle is at 100%. |
| • | The A/C compressor cycling switch pressure is less than 18 psi or greater than 49 psi. |
| • | The A/C High Pressure Cutout Switch pressure is greater than 420 psi. |
| • | Engine speed is greater than 5500 RPM. |
| • | ECT is greater than 121°C (250°F). |
Any of the conditions described above will inhibit A/C compressor relay operation.
Diagnostic Aids
Important: Remove any debris from the PCM connector surfaces before servicing the PCM. Inspect the PCM connector gaskets when diagnosing/replacing the PCM. Ensure that the gaskets are installed correctly. The gaskets prevent water intrusion into the PCM.
| • | The following may cause an intermittent: |
| - | Mis-routed harness |
| - | Rubbed through wire insulation |
| - | Broken wire inside the insulation |
| - | Check the HVAC and PCM connectors for corroded or backed out terminals |
| • | For an intermittent, refer to Symptoms . |
Test Description
The numbers below refer to the steps on the diagnostic table.
-
This step tests if the A/C compressor clutch is engaged when there is no command to be engaged.
-
This step tests if the A/C compressor clutch is functioning. If the A/C clutch operates, inspect for poor connections throughout the system.
-
The A/C clutch relay is located in the underhood electrical center. This step tests the PCM and the A/C clutch relay control circuit.
-
There should be no A/C request when the HVAC control module is in the OFF position.
-
The A/C request circuit is shorted to a voltage between the A/C high pressure switch and the PCM if the scan tool indicates an A/C request when the switch is disconnected.
-
This step tests for a short to ground on the A/C relay control circuit.
-
This step tests for a short between the A/C relay control circuit and any other circuit in the PCM harness connector.
Step | Action | Value(s) | Yes | No | ||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
1 | Did you perform the Powertrain On-Board Diagnostic (OBD) System Check? | -- | ||||||||||||
|
Important: This diagnostic table assumes the following:
Is the A/C compressor clutch engaged? | -- | |||||||||||||
Does the A/C compressor clutch engage? | -- | System OK | ||||||||||||
4 |
Important: Refer to schematic for circuit details Are both fuses for the A/C clutch relay OK? | -- | ||||||||||||
5 | Monitor the A/C Request using a scan tool. Does the scan tool display A/C Request as YES? | -- | ||||||||||||
6 | Monitor the A/C compressor cycling switch using a scan tool. Does the scan tool display A/C compressor cycling switch as Closed? | -- | ||||||||||||
Does the test lamp turn ON and OFF when commanded? | -- | |||||||||||||
8 | Probe both A/C clutch relay B+ supply circuits at the underhood electrical center using the test lamp J 35616-200 connected to ground. Does the test lamp illuminate for both B+ circuits? | -- | ||||||||||||
9 | Jumper the A/C clutch circuit to the B+ circuit using a fuse jumper wire. Refer to Using Fused Jumper Wires in Wiring Systems. Does the A/C clutch engage? | -- | ||||||||||||
10 |
Does the test lamp illuminate? | -- | ||||||||||||
11 | Connect the test lamp J 35616-200 across the A/C clutch harness connector. Does the test lamp illuminate? | -- | ||||||||||||
Monitor the A/C Request using a scan tool. Does the scan tool display A/C Request as YES? | -- | |||||||||||||
Disconnect the A/C high pressure cutout switch located in the rear of the A/C compressor. Does the scan tool display A/C request as YES? | -- | Go to HVAC control module | ||||||||||||
14 |
Does the DMM display a voltage? | -- | ||||||||||||
15 |
Do any of the circuits display a resistance within the specified range? | 0-2ohms | ||||||||||||
16 | Disconnect the A/C clutch relay from the underhood electrical center. Does the A/C clutch disengage? | -- | ||||||||||||
17 | Probe the A/C clutch relay control circuit at the underhood electrical center using the test lamp J 35616-200 connected to B+. Refer to Probing Electrical Connectors in Wiring Systems. Does the test lamp illuminate? | -- | ||||||||||||
Does the test lamp illuminate? | -- | |||||||||||||
Test continuity from the A/C clutch control circuit to all other circuits in the PCM harness connector using the DMM J 39200 . Refer to Testing for Continuity in Wiring Systems. Do any of the circuits display a resistance within the specified range? | 0-2ohms | |||||||||||||
20 |
Does the DMM display near the specified value? | B+ | Go to HVAC control module | |||||||||||
21 |
Does the scan tool display A/C request as YES? | -- | ||||||||||||
22 |
Does the DMM display continuity? | -- | ||||||||||||
23 | Test continuity from the A/C request circuit to battery ground using the DMM J 39200 . Refer to Testing for Continuity in Wiring Systems. Does the DMM display continuity? | -- | ||||||||||||
24 |
Does the DMM display near the specified value? | B+ | ||||||||||||
25 | Jumper the A/C compressor cycling switch connectors using a fused jumper wire. Refer to Using Fused Jumper Wires in Wiring Systems. Does the scan tool display A/C compressor cycling switch as closed? | -- | ||||||||||||
26 |
Does the DMM display continuity? | -- | ||||||||||||
27 | Test continuity from the A/C compressor cycling switch signal circuit to battery ground using the DMM J 39200 . Refer to Testing for Continuity in Wiring Systems. Does the DMM display continuity? | -- | ||||||||||||
28 | Is the A/C fuse open? | -- | ||||||||||||
29 |
Does the test lamp illuminate? | -- | ||||||||||||
30 |
Does the test lamp illuminate? | -- | Go to Air Conditioning Clutch Coil Removal in HVAC Systems with AC Manual | |||||||||||
31 |
Does the DMM display continuity? | -- | ||||||||||||
32 | Repair the open circuit for the circuit that did not illuminate the test lamp. Refer to Wiring Repairs in Wiring Systems. Is the action complete? | -- | System OK | -- | ||||||||||
33 | Repair the open A/C clutch circuit between the relay and the clutch. Refer to Wiring Repairs in Wiring Systems. Is the action complete? | -- | System OK | -- | ||||||||||
34 | Replace the A/C clutch relay. Is the action complete? | -- | System OK | -- | ||||||||||
35 |
Did you find and correct the condition? | -- | System OK | Go to Air Conditioning Clutch Coil Removal in HVAC Systems with AC Manual. | ||||||||||
36 | Repair the open A/C clutch ground circuit. Refer to Wiring Repairs in Wiring Systems. Is the action complete? | -- | System OK | -- | ||||||||||
37 | Repair the A/C request circuit for a short to voltage between the PCM and the A/C high pressure cutout switch. Refer to Wiring Repairs in Wiring Systems. Is the action complete? | -- | System OK | -- | ||||||||||
38 | Repair the A/C request circuit for a short to voltage to the circuit that had continuity. Refer to Wiring Repairs in Wiring Systems. Is the action complete? | -- | System OK | |||||||||||
39 | Repair the short to voltage between the A/C clutch relay and the A/C compressor clutch. Refer to Wiring Repairs in Wiring Systems. Is the action complete? | -- | System OK | -- | ||||||||||
40 | Replace the A/C clutch relay. Is the action complete? | -- | System OK | -- | ||||||||||
41 | Repair the grounded A/C clutch relay control circuit between the PCM and the A/C clutch relay. Refer to Wiring Repairs in Wiring Systems. Is the action complete? | -- | System OK | -- | ||||||||||
42 | Repair the short between the A/C clutch relay control circuit and the circuit that had continuity. Refer to Wiring Repairs in Wiring Systems. Is the action complete? | -- | System OK | -- | ||||||||||
43 |
Did you find and correct the condition? | -- | System OK | |||||||||||
44 | Replace the A/C high pressure cutout switch. Refer to Compressor Control Switches Removal in HVAC Systems with-A/C Manual. Is the action complete? | -- | System OK | -- | ||||||||||
45 | Repair the open A/C request circuit between the PCM and the A/C high pressure cutout switch. Refer to Wiring Repairs in Wiring Systems. Is the action complete? | -- | System OK | -- | ||||||||||
46 | Repair the A/C request circuit for a short to ground. Refer to Wiring Repairs in Wiring Systems. Is the action complete? | -- | System OK | -- | ||||||||||
47 |
Did you find and correct the condition? | -- | System OK | |||||||||||
48 | Replace the A/C compressor cycling switch. Refer to Pressure Cycling Switch Replacement in HVAC Systems with-AC Manual. Is the action complete? | -- | System OK | -- | ||||||||||
49 | Repair the open A/C compressor cycling switch ground circuit. Refer to Wiring Repairs in Wiring Systems. Is the action complete? | -- | System OK | -- | ||||||||||
50 | Repair the open A/C compressor cycling switch signal circuit between the PCM and the switch. Refer to Wiring Repairs in Wiring Systems. Is the action complete? | -- | System OK | -- | ||||||||||
51 | Repair the grounded A/C compressor cycling switch signal circuit between the PCM and the switch. Refer to Wiring Repairs in Wiring Systems. Is the action complete? | -- | System OK | -- | ||||||||||
52 | Replace the Underhood Electrical Center. Refer to Underhood Fuse Block Replacement in Engine Electrical. Is the action complete? | -- | System OK | -- | ||||||||||
53 | Repair the grounded circuit between the A/C clutch and the IGN E fuse or replace the shorted A/C clutch diode. Refer to Wiring Repairs in Wiring Systems. Is the action complete? | -- | System OK | -- | ||||||||||
54 |
Did you find and correct the condition? | -- | System OK | |||||||||||
55 |
Important:: Program the replacement PCM. Refer to Powertrain Control Module Replacement/Programming . Replace the PCM. Is the replacement complete? | -- | System OK | -- | ||||||||||
56 | Repair the open A/C Clutch relay control circuit between the Underhood electrical center and the PCM. Is the action complete? | -- | System OK | -- |
