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Why Is the Heater in My Car Blowing Cold Air and Not Heat?

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JP993 is a self-confessed car and motorcycle addict, having saved thousands over the years working on and maintaining his vehicles himself.

Now that the cold weather is back, we'll be whacking the car's heater on the second we turn the key. Or not, if your car heaters are not working. They work by using the heat in the coolant system that circulates around the car's engine to cool it.

That sounds a little odd right? Well, when I say cool, I mean keep to an optimum temperature, around 80 to 90 degrees. So this is where the heat comes from, your cooling system. That's why you won't get heat until the car has been running for a couple of minutes. As the engine gets hotter, so does the coolant.

Because we rely on the coolant system to provide us with heat through our heaters, there are now a few components that can fail and mean that you'll never get heat out of your car heaters.

The most common culprit for your heaters not working is a faulty thermostat. These clever yet very simple and cheap contraptions regulate the water circulation on initial startup. They're easy to purchase and simple to replace if you have a little mechanical knowledge.

A thermostat, which will be located near the top of your engine, sits closed shut when the water is at ambient temperature, so when the car is left parked up.

When you start your engine, the thermostat stops the water circulation around the engine. This lets the engine warm up quickly and get the oil to its optimum temperature, vital for a healthy engine.

As the temperature rises to around 60 degrees, the thermostat opens up and lets the water circulate around the engine and through the radiator.

All this happens in a matter of minutes in normal weather. If, however, your thermostat has seen out its days, it will remain open. So on initial startup, the cooling system is working straight away. Your engine doesn't have a chance to warm up and your coolant stays at a temperature that won't give you any heat.

I've talked about the most common problem that is causing your heaters to not have heat but let's take a look at a few other things that can be the reason.

To have heat, you need:

  • enough water in your engine,
  • a working thermostat,
  • a working heater and heater controls,
  • and a cooling system that doesn't leak.

If you take short journeys, and your thermostat is broken, you'll never get the engine hot enough to produce any heat. A little test you can do is leave the can running, stationary at home and take a look at your temperature gauge that should be in your dash.

Once you see it get to the middle turn on your heaters and see if you're getting heat. If you are getting heat, your thermostat needs changing.

If you can't get heat no matter how long you leave the car running, I'm going to show you some checks you can do to find what the problem is.

If you're not comfortable with mechanics then read still read on so you know what to expect when you take your car to a mechanic. This problem is relatively cheap to fix. Replacing heater matrices or head gaskets is where the costs become high.

What to Check If Your Car Heater Blows Cold Air

  • Is there enough water and antifreeze in the engine?
  • Is the thermostat working?
  • Is the heating system blocked by an airlock?
  • Are the heater controls broken?
  • Is there a water leak?

1. Is There Enough Water in the Car?

Your heater uses the heat from the coolant circulating around the engine. You should also have antifreeze in your coolant mixture, this not only stops the coolant from freezing inside your engine but also stops it from corroding. The heater is higher up than the rest of the cooling system, and thus last in line for coolant. Thus the first thing you should do, if you have no heat, is to see if there is, in fact, enough coolant in your engine.

You can do this by lifting the bonnet (the hood) and looking at the header tank, which collects overflow coolant from the radiator. This is a large tank, usually clear plastic, with a conspicuous cap, rubber hoses coming off of it, and "Max" and "Min" markings on it. It is positioned a little higher than the radiator, usually to one side or the other of the engine, directly above a wheel.

If this tank is empty, you can fill it back up with ordinary water; you can add some antifreeze if you want. If your header tank is full then proceed to the next step. If you are not certain which is your header tank, ask a friend, or take the car to a local garage.

2. Is Your Thermostat Working?

As mentioned before, the thermostat decides when to let water circulate around your engine. A simple way to find out if your thermostat is working without using any tools is to see if your temperature gauge is giving you a reading on the dash.

If the needle never moves or it's 30 minutes before it does, then your thermostat is most likely broken.

Your temperature gauge should be giving a reading or start to move within 10 minutes of starting the car. If you're noticing you're starting to get heat after driving a while this would also indicate the thermostat is broken.

If the nice warm heat doesn't last very long, this is because you're drawing the heat away from the circulated water. Check your temp gauge again and if starts to fall whilst you have the heaters on, the thermostat is broken.

They're cheap and your neighbouring handyman can fit one.

3. Is the System Blocked by an Air Lock?

Sometimes even with water in the system and a working thermostat, you can still get no heat; the flow of water in the heating-and-cooling system may be blocked by air or dirt.

One possible cause is an air lock in the cooling system. If your system has a bleed port or bleed screw, and you can find it, you can fix this air lock yourself. Run the engine until the fan kicks in. Once your fan has come on, look around the radiator for a bleed port or bleed screw. This is something that can be turned with a screwdriver. Once you turn it anti-clockwise, you should hear a hiss; this is the air being released.

4. Are the Heater or Heater Controls Broken?

Even though most problems with the car heater are not caused by the heater itself but by the cooling system or the thermostat, it is still possible the heater itself may be clogged or broken. Or the heater controls may be stuck or broken. In either case, there is a chance of a cheap or do-it-yourself fix, as shown in the video below.

Toyota Heater and Control Valve

5. Water Leaks? Find Them!

An engine that keeps losing water is a big problem, and not just because low water levels will keep your heater from putting out enough heat. A car that is not getting coolant will heat up and damage itself permanently. If it leaks water, you need to find the source. It can be a split hose, leaky radiator, the water pump, or even worse, the head gasket. Finding the leak can be a pain in the butt too, as even a tiny hole can let a lot of water out while the system is under pressure from being driven.

But if the weather is cold, that makes your investigation easier. Make sure the engine has run long enough to get good and hot and make sure the coolant is topped up. Then, if there is a leak, the hot water escaping will turn to steam when it hits the cold atmosphere. Open the bonnet (hood) and look for steam along the hoses, where the water pump is, and along the radiator. Also, look inside your car—if your windows steam up, or the carpet inside the front of your car gets wet, your leak could be inside the car, behind the dashboard. It could be the heater matrix itself (the heater core) or a split hose.

If the leak turns out to be in the radiator, you can save the cost of a radiator, at least for a while, with products that stop leaks in a car's cooling system. You can also buy a repair bandage for leaking hoses, but this is a temporary measure. Hoses are rubber and don't last forever; they have to be replaced every few years.

Sometimes water loss is caused by a knackered water pump. Telltale signs of a broken water pump include a constant rough metallic sound when the engine is running, or water trickling down the side of the engine. The water pump is a vital part of the engine, and if it's broken it needs to be changed as soon as possible. Often it runs off the cam belt ("timing belt"), and if the water pump destroys itself it will take out the cam belt and the engine along with it. Consider replacing an old water pump as part of routine maintenance, along with the replacement of the cam belt and accessory belts, if you have an old car and want to keep it a few years.

A leaking head gasket is the worst news at all; it means your engine has lost its integrity, and your car needs major repairs right away, assuming you want to keep it.

Common Heater Problems in Different Makes and Models and How to Deal With Them

Here's how to deal with common heater problems in Jeep Liberty, Jeep Wrangler, Mini, and Vauxhall Corsa cars.

1. Jeep Liberty

So if you've tried all of the above and you still have no heat from your heaters in your Jeep Liberty, there are a couple extra things you can do for this model to get the heat bellowing back out of your heaters.

There is a downside: if you're not handy with the spanners you should take your car to the garage. But make sure you go with the knowledge below.

The Actuator Fix

If you're still not getting heat to your heaters, and you know the heater core is not blocked due to a clogged system, and you know there's no air in the system because you've bled the system using the bleed nipple on the right-hand side of the radiator, the last thing you can check is an electronic component.

The centre dial of your heater control located in the centre console can fail. This dial, which changes the amount of heat you want, is run by an electronic component called an actuator that controls the amount of hot air that enters the car.

It's a pretty simple job that this actuator does. It opens and shuts the gate of the heater ducting: something a mechanical part used to do.

You can access this actuator in the left-hand foot well. It is the lower actuator that usually fails. Before you take anything off, look at where the actuator is located and mover the dial. If you can't see the teeth of a black cog move as you move the dial (these teeth are just visible) the actuator is stuck or failed.

Remove the actuator and manually open the gate (you'll see the gear the actuator slips onto) by hand. When you see the gate open, run the car, and you should now have heat.

With the actuator plugged in still but not mounted, see if it moves freely. If it's not moving, time for a new one.

You can also test the actuator with a multi-meter if you're handy.

2. Jeep Wrangler 2012 (and Others)

The Jeep Wrangler has a heater actuator issue almost identical to that of the Jeep Liberty. This issue is described below, and then we talk about another known issue with sandy material that clogs the system.

The Actuator Fix

By checking this first, you'll save yourself a lot of time taking things off. The Jeep Wrangler, unfortunately, doesn't have as much access behind the dash as the Jeep Liberty does. But you can find out if you'll need to start taking your dash apart just by taking a look under the dash on the left-hand side.

As with the Liberty, the A/C to heat control is the centre dial on your dash. This opens and shuts the gate behind the dash to determine how much hot or cold air goes into the system. This is operated by an electronic part called an actuator. It simply goes up and down to open and shut the gate.

What you should do is look under the dash and look for a white plastic part that moves when you turn the dial. You may need a light to shine up in there to see it.

If you can see the white plastic moving, then the actuator isn't the problem, and your problem may be sandy sediment, as described in the next section. But if you can see the white plastic part and it's not moving, then your actuator has failed.

As I said, the location of this is a little trickier than on the Jeep Liberty. There is a panel that sits under the steering wheel on the left-hand side that you can remove to gain more access. It may not be perfect to access it, but it will mean you can remove the actuator without removing the entire dash.

Once the actuator is removed you can manually open the gate by turning the gear that the actuator is attached to. Run your engine, and after a few minutes see if you get heat with the gate now in the other position.

With the actuator off but still plugged in, see with a little push on the plug if it now works. If it does, you can decide whether you want to replace it or not.

The Sediment Buildup Fix

If your actuator was fine all along, you may be dealing with a very common and well-known problem, the buildup of sandy sediment in the system.

If you did all of my general tips and there was still no heat, you may want to try flushing the system again. Get the best coolant flush you can afford.

Make sure you dump out the old coolant at the lowest point possible: the left-hand side of the radiator at the bottom. It is tight on the Jeep Wrangler, but in order to get all the gunk out of the system, you need to undo the lowest hose to remove the coolant.

Once you've done this, leave the bottom hose detached, and run a garden hose through the top radiator hose on the right-hand side, going into the engine, to send fresh running water through the system.

Take the radiator cap off and do the same thing through the radiator (it'll come straight out the bottom hose.)

Now locate the two heater core hoses that are at the back of the engine and go into the firewall. Take both hoses off that attach to the metal piping and run the water through one hose, sealing it with your hand, with the flow going towards the windscreen, not down the metal pipes. You should eventually get the water to flow out of the other pipe.

Connect everything back up and fill up your coolant with antifreeze. You'll now want to bleed the system, which is tricky on these models but is the most important part of all of this.

Run the engine until it reaches the operating temperature and starts bleeding the system. If you bleed the coolant system properly you should now get heat from your heaters.

If you don't get heat, it is likely there is still air in the system. Check your heater core pipes for pressure and make sure both are heating up. You can get a garage to pressure-fill your coolant system.

3. (BMW) Mini One Cooper & S

Fixing the heaters on a Mini 2 (BMW) whether it be the One, Cooper or Cooper S, is relatively straightforward and something you can do yourself if you don't mind getting your hands dirty.

If your Mini is relatively old, say around an '07 or older, the reason for your problem could be this. The principle will work on all Minis though.

Over time, the water that is in the engine, which is being constantly heated up and cooled down, starts to thicken due to the elements that are in regular water. This is why your header tank will go brown.

With older cars, also, there's usually been some problems over the course of the cars life, problems like split hoses, leaky radiators, or front crash damage. The cheap fixes for leaky radiators are usually chemical-based products that are designed to fill the split or hole. This stuff will "gum up" to block the leak.

The thing is, the excess gum just ends up circulating around the system. So between that and old coolant, the system gets pretty grimy.

The Fix for Clogging

Get yourself a coolant system cleaner, or flush as they're sometimes called, and run this in your coolant system. Follow the instructions on the bottle for the best results.

As you let this stuff work and break up the gunk from the system, you'll want to undo the lowest coolant hose you can get to on the engine and dispose of this water correctly.

The heater cores on Minis as well as the thermostat are prone to clogging. Thermostats are cheap, so go ahead and replace this if you haven't already.

Now you want to refill your coolant along with some anti-freeze mixed in. Anti-freeze not only stops your coolant from freezing up, but it also stops the coolant from corroding your engine and lengthens the life of your internal engine parts.

You should now get heat from your Mini's heaters.

If you don't, there's one last thing you need to do, and that is to bleed the air from the system. Mini's have their radiators located quite low, and so air is prone to being trapped in the system. Try a regular bleed of the system and see if you get a noticeable difference.

If you still have no joy, you'll need to take your car to a garage and ask them to pressure-fill your coolant. This should be a simple job for them and shouldn't cost too much.

4. Vauxhall Corsa

The problem with the heater on the Vauxhall Corsa (as well as the Renault Clio) is often that there is no power from the heaters at all. This issue has nothing to do with cold air coming out instead of heat. This loss of power is also a common issue on the Renault Clio. Or you may have a dirty fan that is stuck.

Fix for No Power to the Heater

The first thing you're going to want to look at is your fuses. On the back side of the fuse cover, there should be a table of what fuse does what. Find the one for the heaters and check to see if it hasn't popped. If you can't locate the fuse for the heaters, check all of your fuses.

If all of your fuses are ok, the next thing to go on to is the heater resistor. On the Vauxhall Corsa D model, this resistor is located underneath the glove box. You can get to it without removing anything.

You'll see a plug going into a white box with ridge lines on it. You should also see in front, to the left, a cylindrical grey plastic object, which is where your fan sits. When you've located the plug, turn your ignition on, put it in the "1" setting and wriggle the plug; you may find that the fan comes on. After you've tried this, turn your ignition off.

If the fan does come on after a wriggle of the plug, this means your resistor is faulty.

To replace the resistor, undo two bolts on either side of the plug and remove it. Get the part number off of it to make sure you get the same resistor as a replacement. Put in the new resistor and give it a try.

Fix for a Dirty Fan

If the fan didn't come on when you turned on the ignition and wriggled the plug, your resistor may or may not be faulty, but it's also possible that your fan itself is the problem. Dirt may be covering the terminals inside the fan and causing it not to connect properly. To fix this you can simply clean the terminals inside the fan.

You're going to have to remove the glove box to remove the fan. The glove box is held in by four Torx bolts, one in each corner. Once you remove it, you'll see the ducting from the fan to the back of the centre console. Now locate all the bolts on the fan housing and remove the plug.

Once you have the fan out, look inside it, and through the hole where the ducting attaches to see any dirt buildup. To clean the terminals, hold a rag inside this area while you manually rotate the fan. You should see a noticeable difference.

Now, plug the fan back in but don't mount it yet. Put the fan position on the switch to the "off" position and prop the fan up making sure the fan housing is not touching anything. Turn on the ignition. Switch the fan to the "1" position, and it should spin. Be prepared to turn the fan off almost instantly.

Now that you can see your fan working turn off your ignition and replace everything. Remember to put the ducting back.

This article is accurate and true to the best of the author’s knowledge. Content is for informational or entertainment purposes only and does not substitute for personal counsel or professional advice in business, financial, legal, or technical matters.