Common reasons why air conditioners cannot heat properly
If your air conditioner is not heating properly, the common causes can be broadly categorized into " false malfunctions " (which can be checked by yourself) and " hardware malfunctions " (which require contacting customer service or are difficult to fix). It is recommended to check the simplest issues first before considering reporting a repair.
I. Simple self-check (false faults that can be handled by yourself)
1. Incorrect mode/setting : Not switched to heating (sun icon), electric auxiliary heating not turned on; hot air rises, so if the air deflector is facing upwards, it won't feel hot; the air should be directed downwards.
2. Clogged filter : Dust buildup on the indoor unit's filter reduces airflow and heating performance. It is recommended to clean it every 2–4 weeks.
3. Outdoor unit obstruction and poor ventilation : If the outdoor unit is blocked by debris, snow, or enclosures, heat exchange will be poor; if the outdoor unit's heat sink is covered with dust, the heating will also be weak.
4. Normal defrosting : When the outdoor unit frosts up in winter, the air conditioner will automatically defrost. At this time, the indoor unit will stop blowing hot air, the outdoor unit will emit white steam and drip water. This usually lasts for 5-10 minutes and is normal, not a malfunction. Frequent and prolonged defrosting is abnormal.
5. Insufficient capacity and poor insulation : The room is too large, located on the top floor/facing the west, with drafty doors and windows, and the air conditioner cannot keep up with the demand, so it cannot warm up even when running continuously.
6. Low-temperature environment limitation : When the outdoor temperature of a regular heat pump air conditioner is below -5℃, its heating capacity will be significantly reduced. This is an inherent characteristic of heat pumps.
II. Hardware failure (requires a repair technician)
1. Four-way valve (reversing valve) failure : The most typical problem is that the cooling is normal, but the heating is not; the four-way valve is stuck, the coil is burnt out, or there is internal leakage, so the refrigerant cannot switch to the heating circuit. When the outdoor unit is turned on, it runs but blows cold/warm air.
2. Refrigerant (Freon) leakage/insufficiency : Heating performance deteriorates year by year, frost forms on the thick pipes of the outdoor unit, and the outlet air temperature cannot reach the required level; leak detection and repair are necessary before adding refrigerant, do not add refrigerant blindly.
3. Temperature sensor failure : Aging, detachment, or resistance drift of the indoor unit pipe temperature and ambient temperature probes, causing the main board to misjudge the temperature, resulting in failure to start heating, frequent protection, and fault codes (E1/E2/F1, etc.).
4. Damaged electric auxiliary heating PTC : The heat pump itself has weak heating capacity. After the electric auxiliary heating fails, the air outlet is only slightly warm, and the temperature feels very poor on cold days.
5. Outdoor unit component failure : aging of the outdoor unit fan capacitor, failure of the fan motor, failure of the compressor starting capacitor, resulting in the outdoor unit not starting or running at insufficient speed and unable to provide heating.
6. Main control board failure : The main board does not output signals to the four-way valve, electric auxiliary heating, and compressor, and the machine does not enter the heating process.
III. Quick Judgment Tips
After 15 minutes of heating, the temperature difference between the air outlet and return air outlet should be ≥8℃. If the temperature difference is very small, it is basically a problem with poor heat exchange, refrigerant shortage, or four-way valve. If the outdoor unit is covered with thick ice and does not defrost, check the sensor, refrigerant shortage, or outdoor unit dirt and blockage first.
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