Control Assembly, HVAC

7





Open Circuit, Short To Ground Or Short To B+ In A Motor

Fault symptoms
Unable to change air distribution defrost/floor. Unable to adjust heating.

Conditions
When calibrating, the current consumption for all three motors is measured. The current consumption is compared to a stored set-point value. If the current consumption deviates from the set-point value, diagnostic trouble code 7 is set.





Diagnostic procedure

1. Checking operating current to stepping motor winding 1
- Unplug the 6-pin connector to the stepping motor in question.





- Connect a test lamp between pins 1 and 3 on the female connector.





- Run the stepping motor by turning the knob on the MCC panel.





- Both the red and the green LED should light up on the test lamp.

Is the function correct?
YES
- Go to step 2.
NO
- Rectify lead in question.
- Go to step 3.





2. Checking operating current to stepping motor winding 2
- Connect a test lamp between pins 4 and 6 on the female connector.





- Run the stepping motor by turning the knob on the MCC panel.





- Both the red and the green LED should light up on the test lamp.

Is the function correct?
YES
- Replace stepping motor
- Go to step 3.
NO
- Rectify lead in question.
- Go to step 3.





3. Final check
- Calibrate the control panel.





- Delete diagnostic trouble codes in all systems.





- Read out the diagnostic trouble codes in the MCC and perform a function check.

Is the function correct?
YES
- The steps taken to rectify the fault were correct.
NO
- See "Before changing a control module." Before Changing a Control Module