For 1990-2009 cars

### 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 29 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 "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:

• | 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.

1. Checks for the voltage supply from the heater and A/C control.

2. Checks for resistance of the solenoid windings to determine if it is open or shorted.

Step | Action | Value(s) | Yes | No
--- | --- | --- | --- | ---
1 | Was the Air Delivery System Check performed? | -- | Go to Step 2 | Go to HVAC Air Delivery System Check
2 |

1. Disconnect the connector from the recirculation vacuum solenoid valve.
2. Turn ON the ignition switch.
3. Use a DMM to measure the voltage at harness connector terminal 2.

Is the voltage within the specified value?

B+

Go to Step 3

Go to Step 4

3 |

1. Remove the heater and A/C control. For removal procedure, refer to Control Assembly Replacement .
2. Disconnect connector C2.
3. Measure the resistance between harness connector terminal 1 and terminal 22 of C2.

Is the resistance within the specified value?

0-2 ohms

Go to Step 5

Go to Step 6

4 | Locate and repair open circuit between terminal 26 of the heater and A/C control and harness connector terminal 2. Is the repair complete? | -- | Go to HVAC Air Delivery System Check | --
5 | Measure the resistance of the solenoid valve. Is the resistance within the specified range? | 36.4 ohms | Go to Step 7 | Go to Step 8
6 | Locate and repair the open circuit in CKT 921. Is the repair complete? | -- | Go to HVAC Air Delivery System Check | --
7 |

1. Connect the negative lead of the DMM to a good ground.
2. With the positive lead measure the resistance at terminal 22 of C2.

Is the resistance within the specified range?

OL

Go to Step 10

Go to Step 9

8 | Replace the recirculation vacuum solenoid valve. Is the replacement complete? | -- | Go to HVAC Air Delivery System Check | --
9 | Locate and repair the short to ground in CKT 921. Is the repair complete? | -- | Go to HVAC Air Delivery System Check | --
10 |

1. Reassemble connectors removed in previous steps.
2. Install the scan tool and clear all HVAC DTCs.
3. Retest for a DTC 28.

Is a current DTC 28 set?

--

Go to Step 11

--

11 | Replace and reprogram the heater and A/C control. Refer to Control Assembly Replacement . Is the replacement and reprogramming complete? | -- | Go to HVAC Air Delivery System Check | --