Car Heater Diagnosis
Car Heater Troubleshooting Steps:
The heating system in a car is a very simple setup once you take a minute to observe it’s operation and understand the basic theory of how it works, and since it is an easy system it is usually fairly straight forward to diagnose a heater concern.
Today we will be learning how to find the problem when the car does not have sufficient heat when the heater is turned on.
I am going to list the steps below in which I find it easiest to diagnose a no heat issue, everybody will have their own process, so I hope you find this useful!
Step One:
Make sure the engine coolant level is full! I cannot stress this enough. Over half of the no heat issues I have repaired were due to a low coolant level.
The heater works by running hot coolant through the heater core assembly, which then heats the air in the HVAC housing and changes the air outlet temperature.
If the coolant is low it will not have enough pressure to push up and through the heater core, which results in no hot air.
The coolant should be visible in the reservoir, if the coolant looks low/empty then you need to check for leaks, if there are leaks they will usually be visible by inspecting the cooling system hoses/seals/pump/radiator etc.
If you do not see a leak then the next step is using a Coolant pressure tester
Coolant minimum/maximum capacity level indicator
Step Two:
Check the heater core inlet/outlet temperature. If the heater core has hot coolant going in, and no heat coming out that tells us that the heater core is plugged, and not allowing the proper temperature to be achieved.
If you have one hot hose going in and one cool hose then you will need to attempt to get the heater core flushed/unplugged, some have success with this, others do not, I have always preferred to put in a new core, but certain vehicles that can be a pain in the ass, so attempting to flush it may be the way to go if you want to try and save yourself a headache.
If the inlet/outlet hoses are both hot then the problem is not in the heater core.
The easiest way to test the inlet/outlet temperature is by hand, but if you are not sure then you can use a digital Thermometer
Flushing a Heater Core
Step Three:
If the cooling system all tests out good then that leads the problem to the interior temperature blend mechanism.
The blend door is what controls the temperature output at the vents. The door is moved by an actuator assembly that is controlled by the temperature control switch on the dash. If there is heat coming through the heater core and the vents still will not blow hot air then that means there is an issue with the temperature blend system.
Sometimes these will set a trouble code, but most of the time it is something you manually have to verify and diagnose. The majority of the time it is a bad actuator, but it is possible to have a broke/bound up blend door, I have seen some weird things fall into the vents and cause blockages as well.
HVAC Housing
These are the basic steps to check for diagnosing a heater issue. If you verify all of the above is still operating and you have heater issues then it may be a bit harder problem to which you will want to know what you are doing before tackling it. If you need some personal troubleshooting help for a tricky issue let me know, I love to help solve the weird problems!
Stay safe and have fun!
Thanks for sharing this informative article with us about Car Heater. I had no idea about it but i have learned a lot by this article about car heater. now i have learned how to find the problem when the car does not have sufficient heat when the heater is turned on. I have learned A-Z about car heater by this article.
Thanks Again for this informative article…
Hello there! Thanks for sharing these tips, I’ve learnt a lot from this article. With this, I can fix my car anytime I encounter such issue without taking it to the mechanic always for something I can actually diagnose and do manually.
I will immediately save this article so I can go over it again. Thanks for sharing this with me, it’s really helpful!
Hello Gabriel – Very informative post on auto heater repair. Your website is a handy one to keep on hand so I’ll be bookmarking it for future reference and inquires. I have a question: cars heat up much faster than they used to, what technology is responsible for the coolant to heat faster? Thanks!
Hello Nathaniel, thanks for stopping by!
Modern engines burn and get hot a lot faster/more efficient that older designs, so one of the results of this is we have heat a lot faster.
I have to run the engine in my 1995 GMC for about 10-15mins before I have heat, some of the new trucks get heat within 1 or 2 minutes!!
Hello there! Thank you very much for taking out time to share these tips, it’s helpful. Most of the time I know thermostats can cause heater issues, I did not know about the heater core. I am glad to know I can try to flush the heater core before I would need to tear the dash apart to remove it.
Ive learned a lot from this article, thank you!!
Hello!
Thanks for writing an important article. Finding the problem of not having a car heater is an important factor. Most of the countries in the world are icy. For warmer temperatures, the car needs a car heater. I know that a car heater can stop working for a number of reasons. Step by step you have a very good understanding of how to diagnose a car heater. Check radiator coolant level,check fuse,check temperature . It is a bad thermostat that does not allow the engine to overheat. I think every driver needs to have a very good knowledge of car heater diagnosis. You have explained very well in this regard. Thanks for writing this article.
Best of luck.
Thank you Gabriel for taking out some time to share this technical but very vita do it yourself (DIY) skills with us. You have just given me so much confidence in troubleshooting my car Heater Sytem. Just like fixing the winter tyres around November, I can now also control the Heater system before the Cold begins. Wow! this is really awesome.
Awesome, I am glad you found some useful info 🙂