In this article, we’ll examine the reasons why the indoor unit fan of an air conditioner keeps running even when the system is completely turned off. This issue is more common in AC fans powered by alternating current (AC) and controlled via relays or triacs.
1. Conventional Fans with Relay Control
In systems where the fan is controlled by a relay, the relay acts as an electromechanical switch that turns the fan on and off based on commands from the electronic control board.
Possible Cause:
If the relay gets stuck in the “on” position, the fan will continue running even when the air conditioner is off.
How to Check the Relay:
A. Visual Inspection: Look for visible physical damage to the relay.
B. Manual Release: Gently tap the relay with a non-metallic object to attempt to release it.
C. Functional Test: Remove the relay from the electronic board and apply 9–12V DC to it. A clicking sound indicates it’s working properly. Repeat this procedure several times to confirm functionality.
2. Fans Controlled by a Triac
In these systems, the triac regulates the fan’s operation, including turning it on, off, and controlling its speed by managing the flow of electrical current.
Possible Causes of Failure:
A. Triac Short Circuit:
The triac may remain in a continuous conduction state, keeping the fan on regardless of the control signal. In this case, the triac needs to be replaced.
B. Control Circuit Failure:
If the electronic board’s control circuit sends a constant “on” signal due to damaged components like transistors, diodes, or the microcontroller, the triac will stay active.
C. Thermal Overload:
Prolonged use may overheat the triac, causing damage and leaving it in an open state that prevents it from cutting off the current.
D. Current Leakage in the Triac:
Over time, some triacs may allow small amounts of current to flow, which can keep the fan running—particularly in low-power motors.
E. Optocoupler Failure:
The triac is often controlled by an optocoupler, which provides electrical isolation between the low-voltage control circuit and the triac. If the optocoupler fails or sends incorrect signals, the triac will remain in continuous conduction, keeping the fan on.
