In an air conditioner or heat pump system, the fan not turning on when the compressor turns off can be attributed to the following reasons:
Fan delay timer: Some air conditioning systems are equipped with a fan delay timer. This timer is designed to keep the fan running for a short duration (typically a minute or two) after the compressor has turned off. The purpose of the fan delay timer is to allow the remaining cold air in the system to be distributed throughout the room before the fan shuts off. If the fan delay timer is active, it will cause a temporary delay in the fan starting when the compressor stops.
Thermostat settings: The fan operation can be controlled by the thermostat settings. If the thermostat is set to "Auto" mode, the fan will only run when the cooling or heating system is actively running. In this mode, when the compressor turns off, the fan will also stop. If you want the fan to run continuously, you should set the thermostat to "On" mode. In "On" mode, the fan will run continuously, regardless of whether the compressor is running or not.
Malfunctioning fan motor: If the fan motor is faulty or experiencing a malfunction, it may not turn on when the compressor turns off. This can be due to issues such as a faulty motor, wiring problems, or a malfunctioning control board. If you suspect a problem with the fan motor, it is advisable to contact a qualified HVAC technician to diagnose and resolve the issue.
It's important to note that different air conditioning or heat pump systems may have variations in their operation and control settings. Therefore, it is recommended to consult the system's user manual or contact a professional technician for specific troubleshooting and assistance related to your particular system.