How does the heater in my car work?

Nothing is more frustrating than getting into a vehicle you thought had been warming up for 15 minutes, only to discover it’s blowing cold air! The last thing you want to do is spend money on your car heater with the holidays approaching. 

You might be thinking: what causes this? And is this going to break my wallet? Let’s dive into some possible causes and how the heating system works.

While some are simple and others complex, most HVAC systems share the basic components to heat and cool your vehicle effectively. For this article, we will only focus on the heating side of the HVAC System. 

The HVAC System consists of all the Cooling System components, such as the water pump, hoses, thermostat, radiator, and the added component that transfers the heat into the cabin, the heater core. The main components of the heating side of the HVAC System are the heater core, blower motor or fan (the same one used for the A/C), heater control valve(s) (if it has them), and the HVAC controls to make it all work. 

Simply put, the HVAC System works with the cooling system to use the engine’s heat to warm you.

  1. The heat from the engine transfers to the coolant; the coolant circulates through the system.
  2. The heater core (a small radiator) transfers its heat to the air blown across by the blower motor
  3. That air blows out your vents. 
  4. Then you can enjoy the refreshing warm air instead of the blizzard that’s going on outside. 

That’s a win-win for me!

Now that you understand how it works, let’s go over how a car heater can break. The most common issues are:

  • Faulty thermostat
  • Faulty blower motor
  • Electronic issues with heater controls
  • Low coolant level
  • Clogged heater core

The main issue I saw as a technician was a plugged/clogged heater core. This is usually caused by coolant contamination and a lack of a proper coolant-to-water ratio which can lead to excessive rust. Problems occur when this rust flakes off and gets stuck in the tiny passages inside the heater core. 

We only have two real options at this point. If the heater core is completely damaged, we will have to replace it. And most of them are costly to replace. Usually, the vehicle’s entire dashboard must be removed to replace it! 

The next option is performing a cleaning and system service to remove debris and restore the system with new coolant. Here at BG, we accomplish that by using our BG Cooling System Service. This service cannot fix what is already broken, but it can clean up the system to avoid future issues.

BG car honk sticker

We start with our BG Cooling System Cleaner, which removes corrosion, tough residues, built-up scale, oil, and harsh mineral deposits. We use our Cooling System Service tools (such as BG MVP and BG CT2) to remove the old coolant (and all that gunk we just cleaned off the components) and restore the system with new coolant. Then, we top off the service with our BG Universal Super Cool® which protects against foaming and corrosion and restores critical coolant additive balance and coolant pH.

Maintaining the cooling system is critical for your vehicle’s heating system to work efficiently because the two systems work together when heating your vehicle. Not only is it important for the heating system on those cold winter days, but it’s also crucial for the health of your engine.

I recommend regularly inspecting your cooling system at each oil change by visiting your nearest BG Shop. Having the coolant in your engine checked and exchanged regularly will help ensure a healthy functioning engine and cooling system. This will ensure that you are aware of any cooling system issues and can have them repaired while they are still small. And help keep your toes warm in the winter!

Paul Garcia, BG Proving Ground Manager

By Paul Garcia
BG Proving Ground Manager

Paul has over 17 years of experience in the automotive industry. He is an ASE Certified Master Technician, Volkswagon/Audi Master Technician, and Certified Advanced Diagnostic Technician. Paul has been with BG for five years and currently manages the Proving Ground.

Find a BG shop today

Explore our Shop Locator