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Why is My Car Heater Blowing Cold Air?

Why is My Car Heater Blowing Cold Air?
On a cold and frosty morning, as you head out, there's nothing quite as comforting as the warmth and comfort of your car. But nothing would annoy you more than having your car's heater go 'out cold'. Here's how you could go about fixing it.
Rahul Thadani
Last Updated: May 31, 2018
The classic Eagles' song, Hotel California might make cold wind blowing in your hair sound real exciting and fun, but you wouldn't quite enjoy the feeling when you have cold air blowing into your face, when you turn on your car's heater, more so on a cold winter morning! There could be a number of reasons causing your heater to malfunction, and you can play doctor to your car, as you try and resolve the issue.
How Does the Heater Work?
If you really want to try your hand out at fixing your car's heater, you might want to know how it functions. As the name suggests, the heater in your car, is meant to do just that, warm up the car. It might come as a surprise to many, but your car's heater doesn't have any complex electric connections. This, in fact, makes it a relatively safer component for you, to try to fix by yourself. Be well-advised though, if you can't seem to figure it out, the safest bet would be to visit a car technician, rather than meddle with your car too much. It has a very simple mechanism. The engine coolant is pumped through the core of the heater, and a blower blows air through the coils of the heater. The coolant heats up the coils, which in turn warms up the air. This air is then channeled through hoses running out of the heater assembly, and are directed towards the air vents in the car.
Troubleshooting your Car Heater
Now that you have a better understanding of the anatomy and working of the heater assembly, you can go about looking for the cause of the problem. There are a few basic things that you might want to look for, to fix the heater.
Low Coolant
The most common problem, and probably the simplest one to address, is that of the engine coolant. This, almost magical liquid, makes sure that your engine remains cool at all times, and is essential for the circulation of warm air in the car. If the coolant level is low, the heater coil doesn't warm up enough, and the air passing through doesn't get heated up.
Quick Fix
Pop up the bonnet of your car, and look for a clear tank, usually located just by the side of the radiator. It is the tank with rubber hoses coming out of it. You should be able to see the coolant level from outside; check to see that it is in-between the maximum and minimum levels marked on the tank. If the level of the coolant is low, top it up till just a little below the maximum level. This should ideally take care of the cold air blowing through the vents.
Blockage in the Heater Core
Another possible cause of this problem is a blockage in the heater core, or the presence of some trapped air. If the coolant hasn't been changed in a very long time, it could block the flow of warm air. These problems may prevent the air from getting warmed up and passing through the heater core.
Quick Fix
To get rid of this trapped air, a coolant funnel (a funnel with a wide mouth, used to pour in the coolant), may come in handy. First up, you need to carefully loosen the clamps from the firewall (the metal plate in-between the engine and inside of the car), and detach the hose of the heater. Using a garden hose with a sprayer can also aid one in getting rid of some blockage in the heater core. This will clean out the channels, and facilitate the smooth flow of air. This blockage could also cause the engine to overheat.
Faulty Thermostat
The thermostat in your car has a very basic function of regulating the flow of the coolant to the radiator, and the heater. If the thermostat is faulty, it could either let little or too much coolant to flow into the heater, which affects the flow of warm air. This could also greatly affect the performance of the engine.
Quick Fix
Turn on your car after it has been idle for a while, and the engine has cooled down completely. Leave it running for about 5 minutes, and then check to see if the temperature indicator (the little gauge just by the side of the odometer) shows a rise in temperature. If there is no change in the temperature reading, the thermostat might need to be fixed. Once you have it fixed by a mechanic, it should resolve your heater problem too.
Leaky Heat Valve
Sometimes, a malfunctioning heat valve can also cause this problem to arise. If there is a leak in the hose which carries the hot air, it will result in the malfunctioning of the heater.
Quick Fix
Follow the heater hoses all the way to the engine, and check for some loose valves, or broken vacuum lines. If you happen to locate such damage, you could either try to fix it with repair bandages available in the market (which is a temporary fix), or it would be best to get it fixed by a car expert. Also check for proper airflow by adjusting the heat control to the lowest and the highest a few times, in quick succession.
The best way to check the reason behind your car heater blowing cold air AFTER you have verified that there is enough coolant in the radiator, is to touch both the heater hoses that connect to the firewall. If the heater is working fine, both these hoses will be hot to the touch. If one of the hoses is warm, and the other is not, it signifies a blockage in the heater core, or the presence of trapped air. If both the hoses are not warm, it signifies that there is a malfunction in the heating valve, or a lack of proper airflow.
Knowing this basic information can help one understand the cause behind this problem, and can aid in fixing the same. You might find it a little difficult the first time around, but once you get the hang of things, it should not be a problem for you at all.
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