Circuit Description
The A/C system uses a secondary A/C high pressure switch mounted on the high side of the A/C system near the condenser. The powertrain control module (PCM) utilizes this information in order to close the inlet air door recirculation door from the outside air when the A/C refrigerant pressure is above a predetermined threshold. The working pressure of the A/C system is reduced by recirculating the cooler interior air instead of the hot underhood ambient air.
The secondary A/C pressure switch is normally open. The PCM supplies a 12 volt signal to the secondary A/C high pressure switch. The other terminal of the switch is connected to ground. The switch closes when the A/C pressure exceeds a predetermined threshold. The voltage signal from the PCM goes low 0.0 volts when the secondary A/C high pressure switch closes. The PCM then commands the inlet air door closed to recirculate the interior air.
The heating, ventilation, and air conditioning (HVAC) recirculation system consist of the following:
| • | The A/C secondary high pressure switch |
| • | The PCM |
| • | The inlet air door and motor |
| • | The HVAC control module |
The recirculation door is enabled any time the PCM detects the A/C high side pressure more than 350 psi. The minimum on-time for the recirculation door is 40 seconds.
Diagnostic Aids
Important: Remove any debris from the PCM connector surfaces before servicing the PCM. Inspect the PCM connector gaskets when diagnosing or replacing the PCM. Ensure that the gaskets are installed correctly. The gaskets prevent water intrusion into the PCM.
The recirculation button on the HVAC control head must be OFF when performing this diagnostic. Also, if the control circuit from either the HVAC control head or the PCM control circuit is grounded, the air inlet door will remain in the recirculation mode regardless of PCM command or HVAC control head command.
Test Description
The numbers below refer to the step numbers on the diagnostic table.
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This step is testing for a grounded signal wire, or for a secondary high pressure switch that is stuck closed.
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This step tests if the HVAC control module can control the recirculation door. The glove box door can be lowered to view the operation of the recirculation door.
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This step allows the A/C system to build up a higher pressure, and verifies if the secondary A/C high pressure switch closes. The PCM should command the recirculation door to the ON position as seen on the scan tool.
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This step verifies if the PCM can control the recirculation door. The glove box door can be lowered to view the operation of the recirculation door.
Step | Action | Value(s) | Yes | No |
|---|---|---|---|---|
1 | Did you perform the Powertrain On-Board Diagnostic (OBD) System Check? | -- | ||
2 |
Important: This table assumes the A/C system works and is functioning properly. The HVAC System Check must be performed before proceeding with this diagnostic table. This table only diagnoses the PCM control of the A/C recirculation mode door. For HVAC control of the recirculation mode door diagnosis, refer to Function Test in HVAC Systems for further diagnosis. Did you perform the HVAC Functional Check? | -- | Go to Function Test in HVAC Systems | |
3 |
Important: The A/C refrigerant pressure must be below the specified value for the remainder of the table unless instructed otherwise.
Is the A/C high side pressure below the specified value? | 350 psi | Go to Function Test in HVAC Systems | |
Monitor the Secondary A/C high pressure switch using a scan tool. Does the scan tool display the secondary A/C high pressure switch as Open? | -- | |||
5 | Disconnect the secondary A/C high pressure switch located near the condenser. Does the scan tool display the secondary A/C high pressure switch as Open? | -- | ||
Did the sound of air movement increase when you selected the HVAC recirculation mode or did the recirculation door close? | -- | |||
7 |
Does the DMM display a voltage near the specified value? | B+ | ||
8 | Jumper the secondary A/C high pressure switch terminals together using a fuse jumper wire. Does the secondary A/C high pressure switch parameter change from Open to Closed? | -- | ||
|
Notice: Monitor the engine coolant temperature on the scan tool as you perform this step. Do not allow the engine coolant temperature to exceed 110°C (230°F) as engine damage will occur.
Does the secondary high A/C pressure switch change from Open to Closed when the A/C pressure reaches near the specified pressure? | 350 psi | |||
Does the sound of air movement increase or does the recirculation door close after about one minute? | -- | System OK | ||
11 |
Does the DMM display OL? | -- | ||
12 |
Important: The engine must be operating when disconnecting the C100 connector. The Class 2 Serial Data circuit is open when C100 connector is disconnected. The scan tool will not communicate with the C100 disconnected. Clear any DTCs that set after the repairs are complete. Does the DMM display more than the specified value? | 5 V | Go to Air Inlet Actuator Inoperative in HVAC Systems | |
13 |
Does the test lamp illuminate after about one minute? | -- | ||
14 |
Is the resistance between the specified range? | 0-5 ohms | ||
15 | Test for continuity of the HVAC recirculation mode door control circuit at the PCM harness connector to ground. Refer to Testing for Continuity in Wiring Systems. Does the DMM display OL? | -- | ||
16 |
Is the resistance between the specified range? | 0-5ohms | ||
17 | Test for continuity for the secondary A/C high pressure switch signal circuit at the PCM harness connector to ground. Refer to Testing for Continuity in Wiring Systems. Does the DMM display continuity? | -- | ||
18 | Replace the Secondary A/C high pressure switch. Refer to Pressure Cycling Switch Replacement in HVAC Systems with AC Manual. Is the action complete? | -- | System OK | -- |
19 | Repair the open, grounded, or shorted Secondary A/C High Pressure switch signal circuit. Refer to Wiring Repairs in Wiring Systems. Is the action complete? | -- | System OK | -- |
20 |
Did you find and correct the condition? | -- | System OK | |
21 |
Important:: Program the replacement PCM. Replace the PCM. Refer to Powertrain Control Module Replacement . Is the action complete? | -- | System OK | -- |
22 | Repair the open secondary A/C high pressure switch ground circuit. Refer to Wiring Repairs in Wiring Systems. Is the action complete? | -- | System OK | -- |
23 | Repair the open, grounded, or shorted HVAC recirculation mode door control circuit. Refer to Wiring Repairs in Wiring Systems. Is the action complete? | -- | System OK | -- |
24 | Repair the poor connection at the C100 connector. Refer to Testing for Intermittent Conditions and Poor Connections in Wiring Systems. Is the action complete? | -- | System OK | -- |
