Why is the warm air from the AC not heating properly?
3 Answers
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.
Having driven for over twenty years, I've encountered the issue of the car heater not producing warm air quite a few times. Usually, it's due to low coolant levels or a leak, preventing the engine from reaching the proper temperature to generate heat. Other causes include a clogged heater core from accumulated dust or air bubbles, a stuck thermostat that won't open, or a faulty temperature sensor misreading the temperature. It's particularly uncomfortable when this happens during winter drives, leaving the car chilly. My first step is always to pull over and check the coolant level, topping it up with professional antifreeze coolant. However, it's best not to attempt DIY repairs—take it to a professional shop for a thorough inspection of the hoses and heater core. Regularly changing the coolant and filters can prevent clogs, and never let the problem escalate into a major repair. Safe driving is paramount; if the heater isn't working, reduce your speed to prevent foggy windows and impaired visibility.
Every winter before driving, I make it a habit to test if the heater blows warm air. If it blows cold air, the AC settings might be incorrect, such as having the external circulation on which draws in cold air. Minor coolant leaks are also common, so I check the coolant reservoir under the hood and add some distilled water as an emergency measure if the level is too low. Incorrect fan switch positions or dust buildup can affect heating efficiency, so I try cleaning the air vent filters. A temporary fix: start the car and let the engine warm up for five minutes, then increase the temperature and fan speed—sometimes it works. After learning some car maintenance tips, I bought a test pen to check the system voltage. Don’t ignore potential minor issues; waiting until the fan motor burns out is troublesome. Addressing problems early saves both hassle and money.
