The system switched the flow direction of the refrigerant through a component called “four-way valve”.
At this point, the compressor still compressed the refrigerant into a hot and high-pressure gas, but it was first pumped into the heat exchanger of the indoor unit (which functioned as a condenser at this time).
The hot refrigerant released heat to the indoor air in the indoor unit and then cooled down to become a liquid, providing warm air for the indoor area.
The liquid passed through a throttling device and entered the heat exchanger of the outdoor unit (which functioned as an evaporator at this time), absorbing the heat from the outdoor air (even if it was very cold outside, there was still heat in the air), evaporating into a gas and finally returning to the compressor.
Summary: In the heating mode, the compressor drives the refrigerant and “carries” the heat from the outside to the inside.
However, there is a limitation to heat pump heating:
When the outdoor temperature is extremely low (for example, below 0°C or 5°C, depending on the model), the amount of heat in the outdoor air decreases, the evaporator gets frosty, causing the system’s efficiency to drop sharply and the heating effect to deteriorate.
Phase 2: Heating tube auxiliary operation (electric auxiliary heating)
When the compressor (heat pump) alone is unable to meet the indoor temperature requirements, the heating tubes start to work in conjunction.
The function of the heating tube:
The heating tube (usually a PTC ceramic heating element) is directly installed near the outlet of the indoor unit.
When the air blown out by the indoor unit fan has been preliminarily heated by the compressor and then flows through the energized heating tube, it will be heated a second time.
As a result, the temperature of the blown air is higher, which can quickly raise the indoor temperature.
2. How do they “cooperate”?
Logical control: The computer board of the air conditioner monitors parameters such as indoor temperature, set temperature, and system operating pressure.
Trigger conditions:
At the beginning of startup: To quickly reach the set temperature, the system may simultaneously activate the compressor and heating tubes.
Low outdoor temperature: When the detected outdoor coil temperature is too low or the heating efficiency decreases, the heating tubes will be automatically activated.
Large temperature difference: When the set temperature and the actual indoor temperature have a large difference, the heating tubes will be activated as an auxiliary.
Working state: At this time, the compressor and heating tubes are running simultaneously. The compressor acts as the main force, transporting heat from the outside; the heating tubes act as an auxiliary, directly converting electrical energy into heat energy to “boost the fire”.
Post time: Oct-28-2025