DTC 028

Schematic:

CIRCUIT DESCRIPTION
The recirculation switch on the control panel is a momentary switch that returns to the rest position after it is pressed to the ON or OFF positions. When it is pressed to the ON position, the heater and A/C control grounds the coil of the recirculation vacuum solenoid valve. Battery voltage is supplied from the heater and A/C control to the solenoid, when the ignition is in the ON position. With voltage supplied and ground provided, the solenoid energizes, and allows vacuum to flow to the recirculation actuator valve.

The heater and A/C control also controls the solenoid valve in the AUTO mode.

CONDITIONS FOR SETTING THE DTC
^ Every 200 ms the heater and A/C control continuously monitors CKT 921 for an open or short to ground.
^ CKT 921 stays at or near zero volts.
^ This fault can only be set with the system OFF.

ACTION TAKEN WHEN THE DTC SETS
^ Stores a DTC 28 in the heater and A/C control memory.
^ The heater and A/C control 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 conditions for the fault is no longer present.

DIAGNOSTIC AIDS
^ If the DTC is a history or an intermittent. Try to perform the tests shown while moving the harness wiring 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:
- Wiring broken inside the insulation.
- Poor mating of the connector halves or a terminal not fully seated in the connector body (backed out).
- Improperly formed or damaged terminals. All connector terminals in the related circuits should be carefully reformed or replaced to insure proper contact tension.
- Poor terminal to wire connection. Inspect for poor crimps, crimping over wire insulation rather than the wire.
^ Test the power and ground circuits before replacing the heater and A/C control.

TEST DESCRIPTION

Steps 1-11:

The numbers below refer to the step numbers on the diagnostic table.
2. This step tests for the voltage supply from the heater and A/C control.
5. This step tests the resistance of the solenoid windings to determine if it is open or shorted.