For 1990-2009 cars

### Circuit Description

When the A/C button is pressed ON, battery voltage is supplied to terminal 2 of the A/C compressor refrigerant pressure switch. The A/C pressure switch is closed when the pressure in the refrigerant line is approximately 180 kPa (36 psi). With the pressure switch closed, battery voltage is supplied to terminal 58 connector C2 of the Engine Control Module (ECM). After receiving the A/C request input, the ECM grounds the A/C compressor relay coil which energizes the relay closing the relay contacts. With the relay contacts closed, the circuit is completed allowing battery voltage to be applied to the A/C compressor clutch coil. The A/C compressor clutch coil energizes and the compressor clutch will now engage.

The heater and A/C control monitors the ECM when it energizes or de-energizes the A/C compressor relay coil. The heater and A/C control monitors the circuit at terminal 9 connector C1. This circuit is in parallel with the control side of the relay coil.

### Conditions for Setting the DTC

• | The heater and A/C control monitors the request circuit for a short to ground every 40 ms on a continuous basis.

• | The request circuit stays at or near zero volts.

### Action Taken When the DTC Sets

• | The heater and A/C control stores a DTC 36 in memory.

• | The heater and A/C control internally disables the output.

### Conditions for Clearing the DTC

• | The conditions for the fault are no longer present.

• | Using a scan tool.

• | A history DTC will clear after 20 consecutive ignition cycles if the condition for the fault is no longer present.

### Diagnostic Aids

If condition not present, refer to Testing for Intermittent Conditions and Poor Connections in Wiring Systems.

### Test Description

The number(s) below refer to the step number(s) on the diagnostic table.

1. Tests for voltage to the ECM and determines if the circuit is complete.

Step | Action | Value(s) | Yes | No
--- | --- | --- | --- | ---
Schematic Reference: HVAC Schematics
1 | Did you perform the HVAC Systems Diagnostic System Check? | -- | Go to Step 2 | Go to Diagnostic System Check - HVAC Systems - Automatic
2 |

1. Disconnect ECM connector C2.
2. Turn ON the ignition, with the engine OFF.
3. Measure the voltage from the A/C request input of the ECM while pressing the A/C switch ON.

Does the voltage measure near the specified value?

12 V

Go to Diagnostic Aids

Go to Step 3

3 |

1. Disconnect the A/C compressor refrigerant pressure sensor.
2. Measure the voltage from the A/C request output circuit of the A/C compressor refrigerant pressure sensor while pressing the A/C switch ON.

Does the voltage measure near the specified value?

12 V

Go to Step 4

Go to Step 5

4 |

1. Connect a 3-Amp fused jumper across the A/C request output circuit and the A/C request input of the A/C compressor refrigerant pressure sensor.
2. Measure the voltage from the A/C request input of the ECM while pressing the A/C switch ON.

Does the voltage measure near the specified value?

12 V

Go to Step 7

Go to Step 6

5 | Test the A/C request output circuit of the heater and A/C control for a short to ground and an open. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 13 | Go to Step 9
6 | Test the A/C request input circuit of the ECM for a short to ground and an open. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 13 | Go to Step 8
7 | Inspect for poor connections at the harness connector for the A/C compressor refrigerant pressure sensor. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 13 | Go to Step 10
8 | Inspect for poor connections at the harness connector for the ECM. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 13 | Go to Step 11
9 | Inspect for poor connections at the harness connector for the heater and A/C control. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 13 | Go to Step 12
10 | Replace the A/C compressor refrigerant pressure switch. Refer to Air Conditioning (A/C) High Pressure Switch Replacement in Heating Ventilation and Air Conditioning. Did you complete the replacement? | -- | Go to Step 13 | --
11 | Important: Perform the programming procedure for the ECM. Replace the ECM. Refer to Engine Control Module Replacement in Engine Controls 3.0L Did you complete the replacement? | -- | Go to Step 13 | --
12 | Important: Perform the recalibration procedure for the heater and A/C control. Replace the heater and A/C control. Refer to HVAC Control Module Replacement . Did you complete the replacement? | -- | Go to Step 13 | --
13 |

1. Use the scan tool in order to clear the DTCs.
2. Operate the vehicle according to the Condition for Running the DTC.

Does the DTC set?

--

Go to Step 2

System OK