HVAC System

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 RUNNING THE DTC
The ignition is turned ON.

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 heater and A/C control does not disable 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 and Poor Connections in Diagrams.
^ Check the power and ground circuits before replacing the heater and A/C control.

TEST DESCRIPTION

Steps 1-5:

Steps 6-13:

The number(s) below refer to the step number(s) on the diagnostic table.
2. Listen for an audible click when the water cut-off vacuum solenoid operates. Command both the ON and OFF states. Repeat the commands as necessary.
3. Tests for voltage at the coil side of the water cut-off vacuum solenoid. The heater and A/C control supplies power to the coil side of the water cut-off vacuum solenoid.
4. Verifies that the heater and A/C control is providing ground to the water cut-off vacuum solenoid.
5. Tests if ground is constantly being applied to the water cut-off vacuum solenoid.