At this point, it is recommended to check the heater core for any blockages. If the inlet pipe is very hot while the outlet pipe is relatively cool, it can basically be determined that there is a blockage, and the heater core should be replaced. There is another situation where the lack of warm air is closely related to the coolant. The car's heat source is generated by the coolant, not the air conditioning compressor. The engine's cooling water needs to circulate to the blower inside the dashboard to blow out warm air. Therefore, insufficient coolant levels may have an impact, and it is necessary to add coolant promptly. The hot air blown out by the car's air conditioning is actually the heat generated by the engine's cooling system being directed into the cabin to produce a warming effect. If the air conditioning's warm air effect is not obvious, it indicates a problem with the hot air intake system. Based on your description of "one of the two pipes connected to the heater core being hot while the other is not," it can be preliminarily determined that there is an issue with the cooling system. The car's warm air is produced by the blower directing the heat from the heater core into the cabin. If the airflow is insufficient or the distribution of hot and cold air is poor, preventing the heat from the heater core from being effectively dissipated, the temperature of the warm air will not rise. In this case, first check if the air filter is dirty or clogged and clean it, replacing it if necessary. Then, inspect the operation of the blower at each speed setting to ensure that each setting reaches sufficient speed. If the knob is adjusted to the warm air position, the airflow is strong, and the direction is normal, but cold air is still blowing out, check whether the control cable for the heater core's hot and cold air flap is detached, whether the heater core's impeller is damaged, or whether the flap has fallen off. After troubleshooting these issues, the warm air should start working properly.
