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Q: AC/heater only work on high.

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The heater and AC only work on high.

The fact that the blower turns on leads me to believe the blower motor resistor is at fault for this problem. The blower motor resistor receives a signal from the controller and adjusts airflow accordingly. The problem could also be in the controller. A certified technician such as one from YourMechanic could properly diagnose your heating issue.

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