Circuit Description
The powertrain control module (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 heating, ventilation, and air conditioning (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 percent. |
| • | The A/C compressor cycling switch pressure is less than 18 psi or more than 49 psi. |
| • | The A/C high pressure cutout switch pressure is more than 420 psi. |
| • | Engine speed is more than 5500 RPM. |
| • | Engine coolant temperature (ECT) is more 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 or 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 J 35616-200 test lamp 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 J 35616-200 test lamp 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? | 0-2 ohms | ||||||||||||
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 J 35616-200 test lamp 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. Refer to Testing for Continuity in Wiring Systems. Do any of the circuits display a resistance within the specified range? | 0-2 ohms | |||||||||||||
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. 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. 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 | |||||||||||
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 | ||||||||||
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. Replace the PCM. Refer to Powertrain Control Module Replacement . 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 | -- |
