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
| • | 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 921. |
Action Taken When the DTC Sets
| • | Stores a DTC 28 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 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 "wiggling" 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: |
| - | Wire insulation that is rubbed through causing an intermittent short. |
| - | 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. |
| • | Check the power and ground circuits before replacing the heater and A/C control. |
Test Description
The numbers below refer to the step numbers on the diagnostic table.
Step | Action | Value(s) | Yes | No |
|---|---|---|---|---|
1 | Was the Air Delivery System Check performed? | -- | ||
Is the voltage within the specified value? | Less than 0.1 V | |||
3 | The problem may be intermittent. Move related harnesses and harness connectors. Refer to Diagnostic Aids. Was a problem found and repaired? | -- | ||
4 | Locate and repair short to B+ in CKT 921. Is the repair complete? | -- | -- | |
5 |
Is a current DTC 29 set? | -- | ||
6 | Replace and reprogram the heater and A/C control. Refer to Control Assembly Replacement . Is the replacement and programming complete? | -- | -- |
