Air Goes Out Of Control

Trouble symptom: 

• The blower rotates even though the blower switch is not turned on.
• The blower motor continues to rotate at high speed. (Not adjustable.)

Trouble causes: 

• Airflow capacity failure
• CAN communication failure
• A/C control panel failure
• Blower motor failure

Wiring diagram: 

Air conditioning system Ref. to WIRING SYSTEM>Air Conditioning System>WIRING DIAGRAM .

Fig 1: Air Conditioning System Wiring Diagram (Air Out Of Control)

Courtesy of SUBARU OF AMERICA, INC.

1. CHECK A/C CONTROL PANEL. 
   1. Turn the ignition switch to ON.
   2. Turn the fan dial to the maximum position.
   3. Using Subaru Select Monitor, check [Blower Fan Level] of the data monitor. Ref. to AIR CONDITIONER(DIAGNOSTICS)>Data Monitor .

   Does [Blower Fan Level] indicate "7"?

   • Yes  : Go to 2. 
   • No  : Replace the A/C control panel. Ref. to HVAC SYSTEM (HEATER, VENTILATOR AND A/C)>Control Panel>REMOVAL .
2. CHECK A/C CONTROL PANEL. 
   1. Turn the fan dial to the minimum position.
   2. Using Subaru Select Monitor, check [Blower Fan Level] of the data monitor. Ref. to AIR CONDITIONER(DIAGNOSTICS)>Data Monitor .

   Does [Blower Fan Level] indicate "1"?

   • Yes  : Go to 3. 
   • No  : Replace the A/C control panel. Ref. to HVAC SYSTEM (HEATER, VENTILATOR AND A/C)>Control Panel>REMOVAL .
3. CHECK HARNESS. 
   1. Turn the ignition switch to OFF.
   2. Disconnect the power transistor connector.
   3. Use a tester to measure the resistance between the power transistor connector and chassis ground.

      Connector & terminal 

      (B57) No. 4 - Chassis ground:

   Is the resistance less than 1 Ω?

   • Yes  : Repair or replace the short circuit of the harness between blower motor and power transistor.
   • No  : Go to 4. 
4. CHECK HARNESS. 
   1. Remove the A/C control panel.
   2. Turn the ignition switch to ON.
   3. Use a tester to measure the resistance between the power transistor connector and chassis ground.

      Connector & terminal 

      (B57) No. 2 - Chassis ground:

   Is the resistance less than 1 Ω?

   • Yes  : Repair or replace the short circuit of the harness between A/C control panel and power transistor.
   • No  : Go to 5. 
5. CHECK HARNESS. 
   1. Connect the disconnected connectors.
   2. Turn the ignition switch to ON.
   3. Use a tester to measure the voltage between the power transistor connector and chassis ground.

      Connector & terminal 

      (B57) No. 2 (+) - Chassis ground (-):

   Is the voltage approx. 9 V when the fan dial is set to 1st, and approx. 3.5 V when set to 6th?

   • Yes  : Replace the power transistor. Ref. to HVAC SYSTEM (HEATER, VENTILATOR AND A/C)>Power Transistor (Auto A/C Model)>REMOVAL .
   • No  : Go to 6. 
6. CHECK A/C CONTROL PANEL. 
   1. Turn the fan dial OFF.
   2. Disconnect the power transistor connector.
   3. Use a tester to measure the resistance between the power transistor connector and chassis ground.

      Connector & terminal 

      (B57) No. 2 - Chassis ground:

   When the fan dial is OFF and other than OFF, does the resistance change?

   • Yes  : Replace the power transistor. Ref. to HVAC SYSTEM (HEATER, VENTILATOR AND A/C)>Power Transistor (Auto A/C Model)>REMOVAL .
   • No  : Replace the A/C control panel. Ref. to HVAC SYSTEM (HEATER, VENTILATOR AND A/C)>Control Panel>REMOVAL .