HVAC System

Schematic:

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 state of the compressor clutch relay through the A/C cutout input circuit.

CONDITIONS FOR RUNNING THE DTC
^ The ignition is ON.
^ The A/C request is inactive (A/C OFF).

CONDITIONS FOR SETTING THE DTC
The heater and A/C control detects an open or short to voltage in the A/C request circuit.

ACTION TAKEN WHEN THE DTC SETS
^ Stores a DTC 35 in the heater and A/C control memory.
^ The heater and A/C control does not disable the output.

CONDITIONS FOR CLEARING THE DTC
^ The condition for the fault is 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 the DTC is a history or an intermittent. Try to perform the test shown while moving the wiring harnesses and connectors, this often can cause the malfunction to appear.
^ When moving related harnesses and harness connectors, visually/physically inspect wiring and connectors for the following:
- Dirt or corrosion on the terminals. The terminals must be clean and tree of any foreign material which could impede proper terminal contact.
Damaged connector body, exposing the terminals to moisture and din, as well as not maintaining proper terminal orientation with the component or mating connector.
- Wire insulation which is rubbed through, causing an intermittent short as the bare area touches other wiring or parts of the vehicle.
^ Test the power and ground circuits before replacing the heater and A/C control.

TEST DESCRIPTION

Steps 1-5:

Steps 6-15:

The number(s) below refer to the step number(s) on the diagnostic table.
2. This step determines if the malfunction is present.
3. This step verifies that the A/C request circuits and the A/C compressor refrigerant pressure switch are not open.
4. This step tests for open contacts in the A/C compressor refrigerant pressure switch.
6. This step tests for a short to voltage in the A/C request circuits. The voltage measurement at the ECM should drop from 12 volts to 6.5 volts when the A/C request is commanded from active to inactive.
7. This step verifies that the A/C compressor refrigerant switch is not internally shorted to voltage.