HVAC System

Schematic:

CIRCUIT DESCRIPTION
When the water cut-off solenoid valve is activated, it allows vacuum to be applied to the hot water control valve. The control valve prevents heated coolant from entering the heater core when the vacuum is applied.

In the air conditioning mode or when cooler air is requested, the heater and A/C control grounds the coil of the water cut-off solenoid valve. When the ignition is in the ON position, battery voltage is supplied from the heater and A/C control to the solenoid. With voltage supplied and ground provided the solenoid energizes, and allows vacuum to flow to the hot water control valve.

CONDITIONS FOR SETTING THE DTC
^ If a short circuit to battery is detected on a low side driver, the controller automatically protects the low side driver by disabling all low side outputs.
^ A short to battery has been detected on CKT 920.

ACTION TAKEN WHEN THE DTC SETS
^ Stores a DTC 31 in the heater and A/C control memory.
^ The fault detection process is repeated 3 times at a fixed interval of 70 ms to allow for debouncing.
^ The heater and A/C control disables the output internally.

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 the DTC is a history or an intermittent. Try performing the tests shown while moving wiring harnesses and connectors, this can often 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 free of any foreign material which could impede proper terminal contact.
- Damaged connector body, exposing the terminals to moisture and dirt, 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.
^ Check the power and ground circuits before replacing the heater and A/C control.

TEST DESCRIPTION

Steps 1-9:

The numbers below refer to the step numbers on the diagnostic table.
2. Tests for voltage to the water cut-off solenoid valve.
6. This step checks for shorted solenoid windings.