Why is My Car Heater Blowing Cold Air? | How does a Car Heater work?

The car heater is a most important part of the engine. The main function of the car heater is to supply hot air in the car cabin. Therefore, proper repair and maintenance of the heater are very important for the proper heat supply inside the car. This article explains the symptoms and reasons of a bad car heater.

What is Heater Core?

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Don’t Remove Your Thermostat! Who Like’s Bad Gas Mileage And Freezing

A heater core is very similar as a radiator employed to heat the passenger compartment of a car. The heater uses a coolant. The cold coolant gets heat from the engine and converts into a hot coolant.

car heater

The hot coolant flows through the coiled tubing of the core. This coolant acts as a heat exchanger between the cabin air and the coolant. Fins attached to the core tube increase surface area and help the fan transfer heat to the air flowing through the core tube, heating the interior cabin.

What is a Car heater blower motor?

The heater blower motor has a unique “squirrel cage” design that draws air into the vehicle’s air conditioning system and forces it to flow through different vents.

Depending on the needs of the passengers and the car, this air flows through either the evaporator or vents. The blower motor requires a large amount of amperage. It is controlled by the blower motor resistor and the central air conditioner switch.

Working of Car Heater 

A car heater is the most important of your vehicle that helps to maintain a comfortable environment inside the car. It helps to heat up the car as well as cools the engine.

Car Heater working

A car heater works in the following way:

  • As you drive the vehicle, your vehicle engine heats up.
  • When the engine heats, a water pump starts, which transfers coolant to the engine water vents.
  • As the coolant circulates in the engine water vents, it extracts engine heat and reduces its temperature up to the normal temperature.
  • When the coolant gets heat from the engine, its temperature increases, and it becomes very hot.
  • The hot coolant enters the radiator via hoses.
  • As you turn on the heater, the heat of the coolant starts going into the heater cores that work as heat exchangers. This process permits the coolant to flow throughout the system. The thermostat uses to handle the coolant flow.
  • As the heat starts to transfer into the heater core, the heating system starts to heat up.
  • When the heat is fully transferred to the air, a fan blows hot air into the passenger compartment of your car and heats the inner side of the car.

Reasons of a Bad Car Heater

Following are the most common reasons of the bad car heater:

  1. Insufficient Coolant
  2. Coolant Leak
  3. Bad Thermostat
  4. Defective Heater Cores
  5. Jammed Blend Door
  6. Damaged or Broken Blower Motor Resistor
  7. Water Leaks
  8. Blown Fuse or Faulty Wiring

1) Insufficient Coolant

The engine coolant is a mixture of antifreeze and water. The engine coolant is very important for the proper operation of the engine. It prevents the engine from overheating. It also acts as a heat source that supports the heating system.

When the system does not have sufficient coolant, the car heater doesn’t produce sufficient heat, and the heater core blows cold air into the car.

Solution: As you observe that your heater is not working properly due to the insufficient amount of the coolant, simply add more coolant up to the desired level.

2) Coolant Leak

The coolant leak is another reason due to that your car heater doesn’t work properly. The shortage of coolant causes the engine to overheat. This problem can lead to the complete failure of your engine.

Solution: Check the coolant leak as you refill your coolant into your car radiator. If there is a leak, immediately drive your vehicle to a technician and ask him to fix it.  

3) Bad Thermostat

Is the thermostat still at “C” after the engine has warmed up? In this case, your thermostat may be defective. A thermostat acts as a valve that closes and opens for the coolant.

A defective thermostat can’t properly send a signal that the engine is warming up. In such condition, the coolant will not properly direct heat from the engine to the heater core air, and the heater core will blow cold air.

Solution: As you observe a defective thermostat, immediately buy a new thermostat and install it for the proper working of the heater.

4) Defective Heater Cores

The heater core plays a big role in heating the car. It has a very similar design as a compact radiator. It consists of a metal tube that takes in and dissipates hot coolant and a fan that expels the heat given off by the coolant.

If the heater cores have been clogged or damaged, you may see the following symptoms:

  1. Mist in the cabin of the car
  2. Sweet smell
  3. The car quickly runs out of coolant
  4. Engine overheating

Solution: You can manually clean the outside of the clogged heater cores, flush the duct of the clogged heater core and remove contamination that blocks it. In severe conditions, you must install a new heater core.

4) Jammed Blend Door

The blend door permits air to enter from the heater to the interior of the car. As your car blend James, air bypasses the heater core, leaving a heater that only blows out cold air.

Solution: Blend door needs to be changed. The jammed mixture is often resolved with other major repairs, such as replacing the water pump.

6) Damaged or Broken Blower Motor Resistor

A bad blower motor resistor can prevent you from adjusting the appropriate fan speed or sucking in air.

Solution: Install a new resistor.

7) Water Leaks

Water leakage is a most common issue with the heating system. Leaks can occur from various locations such as a water pump, radiator, and hoses. If one of these three components is leaking, the car heater can’t work efficiently. Therefore, properly check the water pump, radiator, and hoses before driving.

It is important to fix the car heater problem immediately. Ignoring the problem can lead to bigger and more expensive problems or repairs in the future.

Solution: An efficient heater can make winter more comfortable. If you notice water leaks or if your system is unable to dissipate heat from the vents, contact your local technician to inspect and repair your system.

8) Blown Fuse or Faulty Wiring

Just like a bad HVAC control, the car’s wiring may also damage or short out. In this case, if the driver commands the heater to run, the heater will not work.

Solution: As you observe that the wiring of your heater is faulty, contact the technician and ask him for the proper operation of your car heater. If you have blown a fuse, replace it with a new one.

Read More: Types of Engines

How must does a new Heater Core Cost? 

The new heater core replacement cost depends on many factors. The average replacement cost of the heater core is from $450 to $1100. This cost includes the labor cost and parts cost. Some vehicles use expansive heater cores. Therefore, such heater core has a minimum $1050 or higher replacement cost.

How much does a new Thermostat Cost? 

The cost of the new thermostat depends on the brand type. If you are replacing the thermostat yourself, then the average cost of a new thermostat is up to $50.

How much does it cost to fix a car heater blower?

The average replacement cost of a car heater blower motor is from $360 to $400. The cost of the new parts is from $270 to $285, while the labor cost is from $90 to $115.

Parts Cost$270 to $285
Labor Cost$90 to $115
Total Cost$360 to $400

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FAQ Section

Why is my car heater not getting hot enough?

If your heater is not getting hot enough, it may be because of the cold engine. Turn on the engine and wait for a few minutes until the engine heats up.

If your heater is still not producing enough hot air, you may have a defective thermostat, heater core, insufficient coolant, or coolant leak. In these conditions, stop the car and inspect and repair the faulty part.

Why is my car heater blowing cold air?

The car heater can blow cold air because of different reasons. Most commonly, the car heater blows cold air because of the following reasons:

  1. Inappropriate working or a bad thermostat
  2. Broken blower motor resistor
  3. Insufficient supply of the coolant
  4. Coolant leak
  5. Defective heater Core
  6. Water leaks
  7. Jammed blend door

What are the Symptoms of a Bad Car Heater?

A bad car heater has the following signs: 

  1. Coolant Leak
  2. Cold Air: When the heater doesn’t work properly, it starts blowing cold air inside the car. This is a most common sign of a bad or damaged car heater.
  3. Fog Inside Your Car
  4. Engine overheating
  5. Low coolant level
  6. Non-existing or weak cabin heating
  7. Coolant smell inside the passenger compartment

What are the Symptoms of Bad Car Heater Core?

The signs of a bad car heater core are given below:

  1. Engine overheating
  2. Mist in the cabin of the car
  3. The car quickly runs out of coolant
  4. Sweet smell
  5. Insufficient supply of hot air

How Much Does It Cost to Repair a Car Heater?

The repair cost of a car heater depends on many factors such as the type of repair and the area where you and the labor cost. If you repair it yourself, you will just need to pay for the new parts. However, the average repair cost of the car heater is from $750 to $1100.

What are the parts of the Car Heater?

The car heater has the following major parts:

  1. Heater Core
  2. Reserve Tank
  3. Lower Hose
  4. Water Pump
  5. Transmission Cooler
  6. Fan
  7. Radiator
  8. Upper Hose
  9. Thermostat
  10. Pressure Cap
Read More
  1. Different types of Engines
  2. Working of Air-cooled Engines
  3. Working of Engine Cooling System
  4. Working and types of Water-cooled Engines
  5. Types of Piston Engines
  6. Working and Parts of HVAC System
  7. Working of Heat Pump

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