Car Heater Not Blowing Hot Air is usually due to a lack of coolant, a thermostat that won’t move, a coolant system that won’t let air in, or a problem with the automatic blend doors. A bad heater control valve or AC control unit is another thing that could be wrong. The heater core could also clogged or broken. It could also be AC control vacuum lines are crack in older cars.
It’s important for your comfort and safety that your car has a heater in the winter. When the weather outside is below zero, it can be very hard to drive a cold car. And what’s even worse is that it will be very hard to clear the fog off your windows. A lot of the most common reasons are easy and cheap to fix, which is good news.
1. Broken Blend Door
In new cars, or rather, in all cars with digital climate settings, a Car Heater Not Blowing Hot Air is often caused by a broken blend door. Small electric motors in these cars open and shut vents to direct air flow, and the same motors use to control how much air comes in. That can come from the outside for cold air or through the heater core for hot air.
If the motor for the blend door breaks, it won’t respond to your AC signals, so the door will stay in one place. The door’s hinges can also break, which can lock the mix door. More often than not, though, the blend door and motor get out of sync with the AC settings. Problems with the charging system, an old battery, or other problems that cause power spikes or drops can make that happen.
How to Make It Right
It depends on what the exact cause is before we can fix the problem. To start, the blend door motors re-calibrate and then turn on and off by hand to make sure they work. Professional auto HVAC repair shops can do that very quickly, and it won’t take them more than five to ten minutes. It varies from shop to shop, but it costs around $50 to $100.
That will tell you if the problem is with the mix door or not, which is good. That is, it will tell you if you should look into it further or move on to another possible cause. I’m afraid that the repair shop will have to get to the blend doors and blend door motors if the blend doors don’t work.
Depending on the car, that can take anywhere from five to ten minutes or a whole day. It will cost about $25 for a new blend door actuator and a broken blend door. Once more, work can cost anywhere from $50 to several hundred dollars.
2. Thermostat Won’t Move
In all cars, no matter how old or new they are or how many miles they have on them, a stuck thermostat is a pretty regular problem. There is no direct link between the thermostat and the HVAC system. A small valve called the thermostat opens up when it gets hot, letting water flow through the engine. Close the thermostat is d first so that the engine can get to running temperature as quickly as possible.
When the engine is ready to go, the thermostat opens up so that the coolant can flow through the engine and keep it at the right temperature. When a thermostat breaks, it either stays open or closed. The engine will quickly get too hot if the thermostat is stuck closed. And if it gets stuck open, the Car Heater Not Blowing Hot Air, which is especially bad on open roads.
Let’s go back to the heater. The coolant also goes through the heater core, which warms the air that comes into the vehicle. Coolant and air coming through the vents will both stay cold if the thermostat is stuck open and the engine can’t get to running temperature.
A quick drive on the highway is the best way to see if this is the problem. In five to ten minutes, if the coolant temperature gauge doesn’t rise to the middle or starts to drop, you can be sure that the thermostat is stuck open.
How to Make It Right
A faulty thermostat can fix by getting a new one. Most thermostats are not too expensive. There are cars that cost as little as $6 and as much as $25 or $30. There are some heaters that cost more than $70, but those are the only ones. These prices come from AutoZone as well. It will cost 20% to 50% more to buy an OEM thermostat from a store. Then the price is almost always $25.
It can take anywhere from half an hour to an hour and a half to two hours of work to change a thermostat. That’s between $50 and $150, with $70 being the middle price. You’ll also need to add water, but that’s not important. You can also save money by replacing the thermostat yourself. All you need are some simple tools.
3. Heater core that is clogged or broken
Just like the radiator behind the hood, the heater core is a coolant radiator. This one is smaller and sits inside the dashboard. Since there aren’t many coolant openings in the heater core, it’s the first part of the cooling system to get clog. That will stop the hot water from the engine from getting through.
So the air coming out of the vents is either cold or just warm. It’s also important to note that this only happens in older cars that don’t get their coolant flushed often. The same thing will happen if you put the wrong water into the system.
Another option is a broken heater core, which doesn’t matter how old the car is. Because of flaws in the factory, even brand-new heater cores can leak. The same is true for the coolant lines and attachments.
If there is a leak in the heater core, the house will smell sweet and strong whenever you turn on the heater. You may also notice that the front rugs are wet and that the windows fog up much more quickly and worse.
How to Make It Right
You can clear out a heater core in two main ways. The first and less expensive way is to power flush the whole cooling system. All repair shops with the right tools can do that for you, and the price will be around $200 to $300, based on where you live. The second way is to take out the heater core and clean it by hand.
That works much better, but taking out the heater core in almost all cars takes hours, which makes the cost of labor very high. You should only take out the heater core if you can do it yourself. If your heater core is leaking, a new one will cost between $50 and $150, and the work will take between $200 and $600, or two to six hours.
4. Not enough coolant
As we already said, engine coolant heats the vent air as it passes through the heater core. The heater core will be the first part to run out of coolant if the amount is low. In almost all cars, the heater core is the highest point of the cooling system. That’s how it’s made so that the engine doesn’t go without water if it gets very low.
It’s pretty simple to check the coolant amount and add more. Reading your owner’s guidebook will help you if you’re not sure how to do it. Anyway, all you have to do is open the hood, find the coolant tank, and add either antifreeze or distilled water.
Or even better, antifreeze that has already been mixed. You just need to make sure you get the right kind of antifreeze and put it in the right hole. Going to a place that sells auto parts and finding the right kind of antifreeze is easy. The same is true for finding the coolant reservoir.
5. Air Blocked in the Coolant System
A lot of the time, air gets stuck in the cooling system when there is nothing wrong with the car. Thus, it is important to perform regular coolant changes and bleed the coolant at the same time. Hot spots inside the engine can be caused by air in the cooling system. These can leak the head gasket, damage the cylinder head, and make the engine overheat.
We already said that the heater core is the highest point of the cooling system, so most of the time, air gets stuck inside it. In other words, airlocking means that coolant can’t run through the heater core when air gets inside it.
Unless hot water flows through the heater core, the air coming out of the vents will always be cold. Sadly, the only other signs of air in the cooling system are an engine that overheats (which doesn’t happen very often) and a temperature gauge that moves all over the place (which also doesn’t happen very often).
How to Make It Right
This is the best next step to take if you have reached this point and the problem still doesn’t seem to be fix or if everything seems fine. It’s easy to bleed the cooling system, so there’s no need to try to figure out what’s wrong first. Every car has its own way of bleeding the coolant, but in general, you just take out the small bolts that are in the coolant tubes and wait for the coolant to start coming out of them.
Sometimes the heater has to be on and the engine has to be going. Other times it has to be off. You can find the right way to do it and where the bleeding screws go by looking on forums for your type of car or getting a workshop manual for your car. If you want to pay someone to bleed the system for you, it will take them about 30 minutes of work at most.
6. Bad control valve for the heater
When you turn on the heater, a heater control valve sends the water to the heater core. The liquid goes into the diverter valve and then back to the water pump until then. When it’s open, the liquid flows into the heater core and then into the overflow or expansion tank. The heater control valve is mainly an electric switch. It doesn’t fail very often, but older cars can still have it happen.
Coolant won’t be able to flow through the heater core if the diverter valve breaks and gets stuck shut. This means that the vent air won’t get warmer. There aren’t any other signs that a heater control valve is faulty besides the chance that it starts to leak.
So far, though, everything seems fine, so it’s likely that this is what’s wrong. You can also take the valve off and turn on the heater while the car is off to be sure. You can be sure that the valve is working properly if you can hear or see it open and close.
How to Make It Right
To fix a broken heater control valve, you have to get a new one. Based on the car, new valves at AutoZone can cost anywhere from $15 to $75. Most of the time, it costs around $35.
You should be ready to pay around $100 for an hour of work. If you don’t already know how to fix cars, you should let a professional do this job because changing the control valve requires draining the coolant, adding more, and letting it flow.
7. The AC control unit is broken
Another option is a broken AC control unit, but this doesn’t happen very often. When the AC control unit is faulty, the temperature display usually doesn’t change even if you change the settings. This is a clear sign that it’s broken. However, it’s also possible that it’s not talking to the bled doors, which is not so clear. It’s time to take your car to an automobile HVAC repair shop if you’ve made it this far.
They’ll use the same tools they use to make the blend doors work again to see if the AC control unit is still good. If it turns out broken, the best thing to do is buy a used one, which, based on the car, will cost you anywhere from $15 to $150. You could buy a new one, but it’s more likely to be so ridiculously expensive that it’s better to buy two.
8. AC Control Vacuum Lines That Are Cracked
A vacuum was used to handle the heater blend doors and the heater control valve in some older cars, mostly GM models. Over time, those hoses are very likely to crack. Depending on which line is crack, the AC controls or the heater valve will stop working right away. If you find that your car has vacuum lines, you should check all of them that you can see. If you still can’t find a leak, use a smoke machine.
In conclusion
In an older car with manual AC settings, the first thing you should do if the heater doesn’t work is to check the cooling system. That means the amount of coolant, the thermostat, and how the coolant bleed. Also, if you have a new car with digital climate controls, have an automobile HVAC repair shop re-calibrate and check the blend doors as well as the AC control unit.
If that works, the next best thing to do is check the AC control vacuum lines if you drive a car from the 1990s or earlier. Then, a faulty or clog heater core is the only thing left to consider.
