Why is the warm air from the AC not heating properly?

[DeEleanor]

There are two main reasons why the warm air from the AC may not heat properly: issues with the engine cooling system or malfunctions in the warm air control mechanism. Here are some common causes of insufficient heating in the AC warm air system: 1. Cooling system issues: (1) The thermostat is stuck open or opens too early, causing the cooling system to enter a large cycle prematurely. If the external temperature is very low, the engine coolant temperature won't rise, and the warm air won't heat up. (2) The water pump impeller is damaged or slipping, resulting in insufficient flow through the small heater core, preventing heat from rising. (3) There is an airlock in the engine cooling system, which disrupts proper coolant circulation, leading to high coolant temperature but no warm air. 2. Air filter: Dust on the filter prevents the generated heat from being carried out by the flowing air in time, resulting in insufficient heating. Too much dust accumulation on the AC air filter or blocked ventilation openings (both internal and external) by foreign objects can cause this. The filter's function is to absorb dust from the air. If too much dust accumulates without timely cleaning, it can block airflow, reducing the air output from the vents. This prevents the generated heat from being carried out by the flowing air, leading to insufficient heating.