No Heat in the Car (The Most Common Causes)
Stuck in a freezing car because your heater won't work? Several components could be responsible for this issue. But before diagnosing the heating system, it’s important to understand how it works.
HEATING SYSTEM
The purpose of the heating system is to keep passengers warm during cold weather and to defrost the windows for safe driving. Simply put, when the engine is operating, some of the hot coolant from the engine is directed to the heater core. As the hot coolant enters the heater core, the blower motor moves air through it and directs the warm air into the cabin through the vents. Now, it’s important to note the heating operation is interconnected with the cooling system in your car. Therefore, if some of the cooling components fail, your vehicle won’t have any heat.
CAUSES
LOW COOLANT LEVEL
The first reason your heater might not be working could be as simple as low coolant levels. In order for the heater to work properly, the coolant needs to be at the correct level. If it’s below the level, your heating performance will suffer. You should refill the coolant to the proper level and keep an eye on it over the next few drives. If the coolant gets low again, this likely confirms a leak in the cooling system that will need further inspection.
AIR IN THE COOLING SYSTEM
Another common cause of your heater not working is trapped air in the cooling system. If you've recently replaced the coolant or worked on any part of the cooling system, air could have entered and formed air bubbles. These bubbles can get inside the heater core, blocking the flow of hot coolant and causing cold air to blow from the vents.
To fix this, you can try burping your cooling system, which involves removing the trapped air from the system.
THERMOSTAT
A third possible cause could be a faulty thermostat. When the thermostat is stuck open, coolant flows continuously through the radiator, keeping it cool. This cooler coolant then passes through the heater core, causing the air from the vents to feel slightly warm or even cool. You can do a test to see if the thermostat is the culprit. Start your car and wait approximately 15 minutes. This should be plenty of time for the engine to reach the operating temperature. If it doesn't you might have a stuck open thermostat. With a normal operating thermostat, one radiator hose should feel very hot and the other hose should feel warm. If both radiator hoses feel slightly warm or cold to the touch, this could mean you have a stuck open thermostat.
WATER PUMP
The fourth cause of your heater not working is a defective water pump. The purpose of the water pump is to circulate coolant throughout the cooling system. If it fails, it won’t be able to circulate hot coolant to your heater core resulting in poor heating performance.
Heater core
The next possible cause is a faulty heater core. The heater core could fail in two different ways. It can either get clogged or start leaking. Both will have poor heating performance. The key difference is that if it’s leaking, you'll see the coolant level begin to drop. With the heater on a max position, a quick test you can do is to carefully touch both heater hoses. If you notice one hose is very hot and the other is cold or slightly warm then you could have a clogged heater core. In this case, you can try flushing it out before replacing it to try to save some money.
Heater Control Valve
The next possible cause of your heater not working is a defective heater control valve. It’s important to note that not all cars have this component, so check your owner’s manual. The purpose of the heater control valve is to control the coolant flow into the heater core. If it gets stuck closed, there won't be any coolant reaching the heater core, making your cabin feel very cold. There are three main types of heater control valves: electronic, vacuum-operated, or cable-controlled, so make sure to check which one your vehicle has.
The last thing I want to mention is if your car blows warm air from the vents but the airflow is very weak, you could have a dirty cabin air filter. On the other hand, if there’s no air coming out from the vents, the blower motor or the blower motor resistor could be the culprit.
If you conclude that your car has a bad control arm and you want to repair it yourself, I recommend getting a repair manual here. You can use code “AD10VA” for 15% off one-year subscriptions for any US Order.
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