If your air conditioner is blowing hot air when the outside temperature is cold, it is likely due to one of the following reasons:
Heat Pump Operation: Some air conditioners, particularly those in split systems, are designed as heat pumps. Heat pumps can provide both heating and cooling by reversing the refrigeration cycle. During colder weather, the heat pump extracts heat from the outside air and transfers it indoors to warm up the room. However, if the heat pump is not working correctly or if the outside temperature is extremely cold, the heat output might not be sufficient to warm the room adequately, and it may feel like the air conditioner is blowing hot or lukewarm air.
Incorrect Thermostat Setting: Check your thermostat settings to ensure that it is set to "Cool" or "Air Conditioning." Sometimes, if the thermostat is accidentally set to "Heat" or "Heating," the air conditioner will blow warm air instead of cooling.
Defrost Mode: In heat pump systems, during very cold weather, frost can build up on the outdoor unit's coils. To prevent damage and ensure efficient operation, the heat pump might go into defrost mode periodically. During defrost mode, the system temporarily switches to cooling mode to melt the frost from the outdoor coils. This can cause warm air to be blown into the room.
Refrigerant Issues: If the air conditioner is low on refrigerant or has a refrigerant leak, it can affect the cooling performance and result in warm air being blown into the room.
Blocked or Dirty Air Filter: A clogged or dirty air filter can restrict airflow and reduce the cooling capacity of the air conditioner. This can result in reduced cooling performance and warmer air being blown into the room.
Faulty Components: There could be various faulty components within the air conditioning system, such as a malfunctioning compressor, faulty reversing valve (for heat pumps), or issues with the fan motor, which could lead to the air conditioner not cooling properly.
If you are experiencing this issue, it's best to have a professional HVAC technician inspect and diagnose the problem. They can identify the root cause of the issue and perform any necessary repairs or adjustments to restore the cooling function of your air conditioner.