Circuit Description
The VCM control of the A/C clutch improves the idle quality and the performance by:
| • | 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 ON the air conditioning 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.
Diagnostic Aids
An intermittent may be caused by any of the following conditions:
| • | A poor connection |
| • | Rubbed through wire insulation |
| • | A broken wire inside the insulation |
Thoroughly inspect any circuitry that is suspected of causing the intermittent complaint. Refer to Testing for Intermittent Conditions and Poor Connections in Wiring Systems.
If a repair is necessary, refer to Wiring Repairs or Connector Repairs in Wiring Systems.
Test Description
The numbers below refer to the step numbers on the diagnostic table.
-
Checks for low refrigerant as the cause for no A/C.
-
The A/C request signal circuit consists of the HVAC Control assembly, the A/C high pressure cutout switch, and related wiring.
Step | Action | Values | 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 Refrigerant Recovery and Recharging in Heating, Ventillation and Air Conditioning | ||
2 |
Does the A/C clutch engage within the specified time? | 60 sec | Go to Diagnostic Aids | |
3 |
Does the scan tool indicate a YES? | -- | ||
4 | Monitor the A/C evaporator switch in the scan tool. Does the scan tool indicate a CLOSED switch? | -- | ||
Does the scan tool indicate a CLOSED switch? | -- | |||
6 | Probe pin B of the harness connector with a test lamp connected to B+. Is the test lamp ON? | -- | ||
7 | Replace the A/C Pressure Cycling Switch. Refer to Pressure Cycling Switch Replacement in HVAC. Is the action complete? | -- | -- | |
8 |
Caution: Avoid contact with moving parts and hot surfaces while working around a running engine in order to prevent physical injury. 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 B+ Is the test lamp ON? | -- | ||
10 | Repair the A/C clutch ground circuit. Refer to Wiring Repairs in Wiring Systems. 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 Connector Repairs in Wiring Systems. Is the action complete? | -- | -- | |
13 | Replace the A/C compressor clutch. Refer to Compressor Control Valve Assembly Install in HVAC. 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? | -- | ||
16 |
Does the relay A/C click? | -- | ||
17 |
Is the test lamp ON? | -- | ||
18 | Repair the open in the A/C relay ignition positive voltage circuit. If the fuse is blown, then repair the short to ground on the 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 Systems. Is the action complete? | -- | -- | |
19 |
Is the test lamp ON? | -- | ||
20 | Check for an open or short to voltage in the circuit between the Underhood Fuse Block A/C relay control terminal cavity and the VCM C3 connector pin 1. Did you find a problem? | -- | ||
21 | Repair the open in the circuit between the Underhood Fuse Block A/C relay control terminal cavity and the VCM C3 connector pin 1. Refer to Wiring Repairs in Wiring Systems. Is the action complete? | -- | -- | |
22 |
Is the test lamp ON? | -- | ||
23 | Repair the open in the A/C relay battery feed circuit. If the fuse is blown, then repair the short to ground on the 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 Systems. Is the action complete? | -- | -- | |
24 |
Does the A/C Clutch engage? | -- | ||
25 | Replace the A/C relay. Is the action complete? | -- | -- | |
26 | Repair the open or short to ground in the compressor clutch control circuit. Refer to Wiring Repairs in Wiring Systems. Is the action complete? | -- | -- | |
27 | Check for an open in the A/C cycling signal circuit. Did you find a problem? | |||
28 | Replace the HVAC control assembly. Refer to Control Assembly Replacement in HVAC. Is the action complete? | -- | -- | |
29 | Check for a poor VCM connection. Did you find a problem? | -- | ||
30 | Repair the circuit as necessary. Refer to Wiring Repairs in Wiring Systems. Is the action complete? | -- | -- | |
31 |
Important: The replacement VCM must be programmed. Replace the VCM. Refer to VCM Replacement/Programming Is the action complete? | -- | -- | |
32 |
Does the A/C clutch engage within the specified time? | 60 sec | ||
33 | Does the scan tool display any additional undiagnosed DTCs? | -- | Go to applicable DTC | System OK |
