Circuit Description
The VCM control of the A/C clutch improves idle quality and performance by performing the following conditions:
| • | Delaying clutch engagement until the idle speed is increased |
| • | Releasing the clutch when the idle speed is too low |
| • | Providing additional fuel at the instant the clutch is applied |
The additional fuel smooths the cycling of the compressor.
Turning the air conditioning ON supplies battery voltage through the pressure switches to the VCM. When the VCM receives the voltage on the A/C request signal, the A/C enable relay circuit is grounded. The A/C compressor clutch then engages.
Test Description
The number(s) below refer to the step number(s) on the diagnostic table.
Step | Action | Value(s) | Yes | No |
|---|---|---|---|---|
|
Important: Before using this table confirm that the A/C system has an adequate state of charge. Does the A/C system have an adequate state of charge? | -- | Go to A/C System Diagnosis in the HVAC section | ||
2 |
Does the A/C clutch engage and disengage within the specified value? | 60 sec | Go to A/C System Diagnosis in HVAC | |
3 |
Does the display read YES? | -- | ||
4 |
Does the display read CLOSED? | -- | ||
5 |
Does the scan tool display read CLOSED? | -- | ||
6 | Probe pin B of the harness connector with a test lamp connected to the B+ terminal. Is the test lamp ON? | -- | ||
7 | Replace the A/C Evaporator/Cycling Cutoff switch. Is the action complete? | -- | -- | |
8 |
Is the test lamp on? | -- | ||
9 | Probe the A/C clutch ground circuit at the A/C clutch harness connector with a test lamp connected to the B+ terminal. Is the test lamp ON? | -- | ||
10 | Repair the A/C clutch ground circuit. Refer to Wiring Repairs in Wiring Repairs. Is the action complete? | -- | -- | |
11 | Check for a poor connection at the compressor clutch harness connector. Did you find a problem? | -- | ||
12 | Repair the A/C compressor clutch harness connector. Refer to Wiring Repairs in Wiring Repairs. Is the action complete? | -- | -- | |
13 | Replace the A/C compressor clutch. Refer to Heating and Air Conditioning Is the action complete? | -- | -- | |
14 |
Is the test lamp ON? | -- | ||
15 | Check for an open in the A/C request signal circuit between the HVAC control module and the VCM. Did you find a problem? | -- | Go to A/C System Diagnosis in HVAC | |
16 |
Does the relay click? | -- | ||
17 |
Is the test lamp ON? | -- | ||
18 | Repair the open in the A/C relay ignition feed circuit. A blown fuse or lack of voltage to the fuse may cause other symptoms or DTCs to be present. Refer to Wiring Repairs in Wiring Repairs. Is the action complete? | -- | -- | |
19 |
Is the test lamp ON? | -- | ||
20 | Check for an open or short to voltage in the circuit between the A/C relay control terminal cavity of the UBEC and the VCM C3 connector pin 1. Did you find a problem? | -- | ||
21 |
Is the action complete? | -- | -- | |
22 |
Is the test lamp ON? | -- | ||
23 |
Is the action complete? | -- | -- | |
24 |
Does the A/C clutch engage? | -- | ||
25 | Replace the A/C relay. Refer to A/C Relay Repair and Replacement in HVAC. Is the action complete? | -- | -- | |
26 | Repair the open or short to ground in the compressor clutch control circuit. Refer to Wiring Repairs in Wiring Repairs. Did you find a problem? | -- | -- | |
27 | Check for an open in the A/C cycling signal circuit. Did you find a problem? | -- | ||
28 | Check for a poor connection at the VCM. Did you find a problem? | -- | ||
29 | Repair the circuit as necessary. Refer to Wiring Repairs Did you find a problem? Is the action complete? | -- | -- | |
30 |
Important: Program the new VCM. Refer to VCM Replacement/Programming .
Program the new VCM. Refer to VCM Replacement/Programming . Is the action complete? | -- | -- | |
31 |
Does the A/C clutch engage within the specified time? | 60 seconds | ||
32 | Using the scan tool, select the Capture Info and the Review Info. Are any DTCs displayed that have not been diagnosed? | -- | Go to the applicable DTC table | System OK |
