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Hey guys, ChrisFix here, and with the colder weather around the corner, today I'm going to show you how to diagnose a problem where you don't get heat in your car or truck. Before we begin anything, turn your car or your truck to the run position, and you just want to make sure that your temperature gauge here is low. You do not want it to be in the middle or high, because the first test we're going to do is to check to make sure that we have enough antifreeze in the car. You can't check the antifreeze when the engine is hot.
You get heat in your car because the radiator fluid that gets really hot runs through the engine, through the piping, into your cabin, where there's a mini radiator. That mini radiator holds hot coolant. It's called your heater core, and then a fan blows over your heater core, and that's how you get hot air. When that coolant is cooled just a little bit because you have a fan blowing over it, it gets sent back into the engine. So if you don't have enough coolant, your engine might be able to run at the correct operating temperature, but because the heater core is so high up in the vehicle, there might not be enough fluid to get in here and give you heat inside your car.
The first step we're going to do, since the engine is still cold, is go check the radiator and see if there's enough fluid in here. You just spin the cap counterclockwise, and then when it won't spin any more, you press downwards and spin it until it comes off. Wow, I'm definitely going to need to change this fluid very soon. You can see it's all gunked up, and that will bring me to another reason why you might not have heat, but we'll get to that in a couple of seconds. You can see the coolant is right up to the top here, so this radiator is filled. Now we'll put the cap back on and just twist this clockwise until it firmly snaps into place. You want to make sure that this is on correctly, because this is a pressurized system. Your car might not have a radiator cap like this, so just check your owner's manual. It'll tell you how to check your coolant. That's just one of those basic things that every owner's manual has.
Also, you might have a coolant reservoir that you should check. You could just go in here and see if there's any coolant, and in my case there isn't any coolant, so I'm going to add a little bit. When you're adding coolant to this, you want to go and look. There's a cold fill line you can see all the way down there. It says "cold fill," and that's where you fill this up when the engine is cold. So I'm going to add some coolant. Make sure you check your owner's manual to make sure you're adding the right type of coolant.
Okay, so now we know that our radiator is filled and we've topped off our coolant reservoir, so now we can properly test the heating system and see if we have heat. Filling your radiator up with just a little bit of coolant like this might just be an easy fix for your no-heat problem. So now we're going to go for a ride so that we can heat up our engine. You want the temperature gauge here to be between the C and the H, right in the middle, and that's how you know your car is heated up. At that point you should have heat in your car. So I'm just finishing up my drive, and you can see the engine is at operating temperature. Now that the engine is warmed up, let me show you the other steps to diagnose a vehicle when you don't have heat.
I've been driving around for a little while, and that gauge has been pretty stable right there. But if your car is overheating, then the reason you're not getting heat is because the water pump isn't working. Typically a bad water pump will leak, and the impeller will still spin, but if it doesn't spin, the hot coolant won't be forced into your heater core or even your radiator, so your engine will overheat and you won't get any heat in the cabin. You also might have a problem where your car never gets hot. It doesn't get up to operating temperature, and this could be due to the absence of a thermostat or your thermostat being stuck open. To find your thermostat, all you have to do is follow that top radiator hose into your engine. Once you find your thermostat, it's just two bolts. You unbolt those, take the old thermostat out, put the new thermostat in, and close it up. In this case, since our temperature gauge is right in the middle, we know that the thermostat and water pump are good. Just to let you know, in my truck I actually have heat, everything is fine. I'm just going through steps for you, so if you don't have heat or if you have a little heat, you can diagnose the problem yourself.
After the car is warmed up, we're going to turn the heat on all the way and then put the heat on the floor. My fan is working: it works when it's on low, it works when it's on medium, and it works when it's on high. If your fan only works when it's on high and you're not getting heat or a fan on the lower settings, then your blower motor resistor is probably bad, and I have a video on how to replace that. It's not a big deal. It's a pretty cheap part and it's pretty quick and easy to replace. Now, if your fan doesn't work at all, you have it on all the different speeds and it's not working, then your blower motor is probably bad, and I also have a video on how to replace that. But if your fan does work and you're still not getting heat or it's not very hot, there could be other problems. Let's say the air coming out isn't really hot, like it's a little warm but not as hot as it should be. What that typically is caused by is a clogged heater core.
To check for a clogged heater core, make sure your heat is on, and we're going to go outside to the engine compartment. When we look at our engine compartment, what we want to do is go back to the firewall, typically on the passenger side or somewhere near the middle. You're going to find two hoses. These two hoses go into the firewall, and these are your heater core hoses. With these two heater core hoses, you want to touch them and make sure that both of them are hot. Right now it's about 35 degrees on the blacktop, so imagine how cold it is outside. Then I'm going to turn the laser on so you can see where I'm aiming. I'm aiming right on the hose, and it's about 140 degrees. Now I go to the other one: same temperature, 140. So both of these are the same temperature. They're both warm, they're hot to the touch. Make sure you don't burn yourself when you're doing this. So I know my flow is good. If you have one that's hot and one that's cold, the first thing you want to do is check the heater control valve, which is this right here. In my case, my heater control valve is run by a vacuum. In your case, it might be electronic or mechanical. Either way, all you have to do is turn the heat on and shut the heat off and see if this moves.
So if your valve is working, it'll move in and out. If your valve isn't working, it won't move. If your heater control valve isn't working, you're not going to be able to get heat, because it won't let coolant flow into your heater core, and if that's the case, you just need to replace it. If you just want to set this up real quick so that you have heat without fixing this, all you have to do is take the vacuum line off and then clog up the vacuum line here. You don't have a vacuum leak. Now, if it doesn't open up when you take the vacuum line off, just manually open it up. You can even tape it or rubber band it to something so that it stays open. That's just a temporary fix, but it's something, so you have heat. If you have an electrical one, you can unclip it from the wiring harness and test it to see if it's getting power when you turn the heat on. If it's getting power, your heater valve is bad. If you're not getting power, then there's a problem with the HVAC control under the dash. If your car has a mechanical heater control valve, when you turn the dial for your heat, you move a cable that opens the valve instead of using vacuum or an electrical motor. This cable can disconnect, and many times you just need to pop it back into place to fix the problem. Remember, if you can't find a heater control valve, your car might not use one, so don't worry. In my case, this works fine, so let's move on to the next thing.
To diagnose the other reason why one of your hoses will be hot and the other will be cool or slightly warm: you have a clogged heater core. You can attempt to reverse flush the heater core by taking off both of the hoses and running water through them to flush any gunk that's in there and might be clogging it up. You could use a garden hose, but make sure you use very low pressure, because you could damage the heater core. I have a video on flushing the heater core, and the link to that video will be in the description.
Now, let's say both of your lines are cold and your heater control valve is working properly. You might have air in the system. Since this is one of the highest points in your cooling system, there's a good chance that air could get caught in here. To fix that, all you have to do is bleed your cooling system. Sometimes, with the heater on, a few good revs of the engine will force that air out and let the coolant in.
Now, one of the last things I'm going to go over to diagnose the heater system: if you did all that and none of it worked, you could have a bad blend door actuator. In some cars this is mechanical, in other cars it could be moved with an electrical motor or using engine vacuum. What a blend door does is it's a door that blocks either the air conditioner or the heater. So if you turn your temperature to the cool position right now, the blend door will be blocking the heater core. You don't want air from the heater core, because you just want cold air. If you turn your heat on, then the blend door will be blocking cold air coming from the car. The blend door can also allow both hot and cold air to come in at the same time to get a desired temperature. Typically, if you change your temperature quickly like that, you'll hear a knock, and that's the blend door just slamming shut. I'm going to change this quickly, and we'll see if you can hear it. In mine, you can hear the blend door open and close. It's just that one click or one knock, and it's functioning properly. If you don't hear that on yours when you turn this quickly, or if you hear a clicking, so if I go from here to here and it's making a stripping noise like a click click click click and then it stops, that could be the blend door actuator, which is up under the dash and connected to the blend door. It's just an electrical motor, and the gears strip over time, and then your blend door won't move. So it'll be stuck in either this position or that position, either allowing cool air or hot air into your car. All you would have to do is replace that blend door actuator, and that'll fix the problem. Or, in this case, since it's mechanically connected from the switch to the blend door, you can look behind here for a connector that popped off and just reconnect it. The same goes for a blend door that works off engine vacuum: just look for a loose vacuum hose and reconnect it.
These are the most common problems for no-heat situations. I hope this video helps you diagnose your problem. As always, you can comment below with any questions. Also, remember to give the video a thumbs up, and if you're not a subscriber, what are you waiting for? Hit that subscribe button. The top tip for this video is a basic maintenance tip on how to prevent a no-heat situation, because nobody wants to be left in the cold on their drive. The best way to prevent many no-heat problems is with a coolant flush every few years. If you're unsure whether your coolant needs changing, one way to test it is with a multimeter. With the engine cooled down, take the radiator cap off. Now start your engine and set the multimeter to 20 DC volts. Take one of the leads and put it in the coolant, but only touch the coolant, not the side or the metal of the radiator. Take another lead and put it on the ground. If the reading is 0.3 volts or more, you probably need to change your coolant. There are other methods to test your coolant, and I'll get more into this multimeter method in another video, and the link to that video will be in the description below.