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Hey, Why is My Car's Heater Not Working?

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Four common causes for a vehicle heater not working and their related parts.

Your vehicle's cooling system is responsible for the heat that is generated inside the vehicle. The cooling system has several components that maintain proper engine temperature to provide for proper combustion and low emissions from the exhaust pipe. The secondary by-product of this cooling system is to transfer the heat from the coolant to the inside of the vehicle through a heater core. Once the coolant is transferred through the heater core, climate control blends air to maintain the proper temperature inside the vehicle.

Is The Heater in Your Car Not Working?

The heater isn't working because of issues with the blower motor. This can be caused by internal damage or wiring problems preventing power from getting to the blower motor. However, in less common cases, the issue might be related to something different, like a restricted heater core, faulty blend door actuator, faulty coolant control valve, faulty heater fan, or a stuck-open thermostat.

A car heater not blowing hot air can involve several different car systems! Ignoring heating problems can jeopardize your comfort, create further issues, and drain your wallet.

Consider consulting a skilled expert who can pinpoint and recommend future actions to prevent and fix the broken car heater. This keeps your vehicle running smoothly, allowing you to enjoy a cozy ride worry-free. Remember, if left unattended, a minor glitch can snowball into a major headache.

Let's Get To The Bottom Of It!

  • Q: Is the blower motor unresponsive or working intermittently?

    The blower motor in your car's heater is like a fan that pushes air across. Over time, this motor can wear out and draw more electrical current. When this happens, the wires and connectors can get hot and melt, leading to a weak and intermittent connection. As a result, the blower motor may work sometimes but not always. More rarely, this can trigger the "check engine" light on the dashboard.

  • Q: Is the heater blowing cold air even after warming up the engine?

    Certain vehicles have a valve called the "heater hose control valve." Its job is to restrict the amount of hot coolant that goes into the heater core, which helps improve the effectiveness of the air conditioning system. This valve can operate in different ways: mechanically, by vacuum, or electronically. If this control valve malfunctions, it restricts the hot coolant flow to the heater core. As a result, even after the engine warms up, you won't get any hot air from the heater vents. In rare cases, this might accompany a coolant leak, weak airflow from the vents, and clicking noise under the dashboard.

  • Q: Is the temperature coming from the heater always the same regardless of your adjustments?

    Inside your car's heating and air conditioning system, there's the "airbox." It has plastic doors that control the airflow to manage the temperature. These doors are moved by small motors called "door actuators." If these doors break, the actuator can't control them anymore and gets stuck in one position. Since the doors blend hot and cold air, the temperature won't change, no matter what you set on the control panel. This rarely accompanies a "check engine" light on the dashboard.

  • Q: Is the "check engine" light active on the dashboard?

    The thermostat in your car helps the engine warm up in a calculated time to reduce emissions. But it can get stuck open and break down after wear and tear. When the thermostat sticks open, the engine takes longer to reach its ideal temperature. This warm-up delay is alarming to the engine computer, activating the "check engine" light on the dashboard.

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Vehicle Health Inspection Proof

Explore the following typical inspection results that show a potential cause for the symptom and select the one you believe is similar to your vehicle's issue.

Clogged Heater Core

This proof image confirms the restricted flow in the heater core, which is causing the heating problem in the vehicle.

When the customer brought in their vehicle, they mentioned that the heater only worked while driving at freeway speeds. The heater's temperature wouldn't act right if they drove at normal speeds.

The technician confirms during a test drive that the car heater isn't working. So, it wasn't working as expected.

To diagnose the issue further, the technician conducted a vehicle health inspection. During this inspection, they didn't find any immediate problems related to the customer's concern.

However, to investigate the heating problem, the customer authorized additional diagnostics. Then, the technician used an infrared digital thermometer to read the temperature of specific car parts. They started the engine and measured the temperature at the upper radiator hose, which was 198ºF. 

Then, they checked the temperature of the heater hose going into the heater, which was 199ºF. However, the temperature coming out of the heater core was only 85°F. This temperature difference means the heater core was restricted, reducing coolant flow.

Based on the findings, the technician suggests trying a process called back-flushing the heater core to see if it helps restore proper coolant flow. They recommend replacing the clogged heater core if this attempt doesn't work.

Note that this sort of issue does not only affect small vehicles but can also be a pain for trucks. So, ensure you have a specialized mechanic with truck repair certification in similar cases.

Does the issue look like this? if not accessible your shop will document it
Blend Actuator Failing

The proof picture shows the blend door actuator connector disconnected, taken during additional testings.

A customer brought their vehicle to the shop because it sounded like something was stuck inside the dashboard. A knocking noise was coming from there, but they couldn't figure out what was causing it.

During a test drive, the technician noticed a clicking noise from the dashboard. Unfortunately, the technician found nothing else related during a vehicle health inspection. Therefore, the customer approved additional diagnostics.

The technician started the vehicle and tested different heater settings like defrost, vent, and floor, and the clicking noise ceased. Next, they tried the recirculation and fresh air settings, which were normal.

However, a clicking noise appeared when the technician adjusted the temperature on the driver's side from hot to cold. This led the technician to suspect that the driver-side blend door motor was failing and needed replacement.

The technician disconnected the blend door actuator connector to confirm their suspicion and performed additional power-related tests. As a result, they verified the issue was from the driver-side blend door motor.

Does the issue look like this? if not accessible your shop will document it
Blower Motor Wiring

The proof image shows the melted blower motor electrical connector, which is the cause of the intermittent blower motor functioning.

A customer brought their vehicle to the shop because its heater wasn't working properly. Sometimes, it worked fine in all settings, but in others, only at high-speed settings. They noticed that if they set the blower at high speed, it would work, and then they could adjust it to slower speeds. However, it never seemed to work if they tried starting it at a low-speed setting.

During the test drive, the technician observed that the blower motor worked inconsistently. While doing a vehicle health inspection, the technician found nothing relevant.

After the customer approved additional diagnostics, the technician accessed the blower motor and blower motor resistor under the dashboard. When attempting to back probe the electrical connector to the blower motor, they discovered the connector was melted. 

Nevertheless, the technician tested the voltage to the blower motor by back-probing the connector anyway; they found that the voltage was present at all speeds. This evidence indicated that the blower motor and its pigtail were melted causing the heater to work only sometimes at specific wiring angles, and would need to be replaced.

Does the issue look like this? if not accessible your shop will document it
Heater Control Valve

The proof image shows the failed heater hose control valve, which remains closed even when it is supposed to open with electrical power. This causes the heater to run with low coolant, affecting the engine's cooling system, and is the reason why the heater is not functioning properly.

A customer brought their vehicle to the shop because the heater was not blowing any warm air, and the air conditioner felt like it was always running.

During the test drive, the technician confirmed that the heater was not blowing warm air. As part of the vehicle health inspection, the technician couldn't find any relevant issues. Therefore, the customer approved additional diagnostics.

The technician used an infrared temperature tool to check the engine's operating temperature, which was normal. They also checked the temperature before and after the heater control valve. Before the valve, the temperature was like the engine temperature, but after the valve, it was like the outside air temperature.

After back-probing the heater control valve's electrical connector, they found that the valve solenoid was receiving power and ground, but the valve itself was not opening. So, power was reaching it, but something internally was preventing the valve from working. As a result, the technician concluded that the heater control valve had internal damages and needed to be replaced.

Does the issue look like this? if not accessible your shop will document it
Blend Door Broken

The proof image shows the broken blend door with its actuator removed, revealing the issue causing the lukewarm air problem in the vehicle's ventilation system.

A customer brought their vehicle to the shop because the air from the heater or AC vents was always lukewarm. It didn't get as hot or cold as it should.

During the test drive, the technician confirmed that the air temperature from the AC vent and heater fan remained lukewarm, regardless of the temperature settings on the panel. While doing a vehicle health inspection, the technician found no relevant issues.

After the customer authorized additional diagnostics, the technician used a specialized scanner designed for this vehicle to monitor the blend door's operation. They discovered that the blend door motor constantly turned when switching from hot to cold without making any clicking sound whatsoever.

The technician accessed the blend door motor and removed it from the airbox to investigate further. By adjusting the temperature settings, they observed the motor turning. Upon returning the blend door inside the airbox and observing it, they found that a crucial part of the door was broken, preventing the motor from properly managing the doors. 

To resolve this issue, the dashboard and airbox must be removed to replace the broken blend door entirely.

Does the issue look like this? if not accessible your shop will document it
Stuck Thermostat

The proof image shows the removed thermostat, and you can see that it's stuck open, which prevents the vehicle from warming up as it should and triggers the check engine light to turn on.

A customer brought their vehicle to the shop, and they mentioned two concerns. Firstly, the check engine light was on, and secondly, they noticed the heater wasn't warm. They used to feel a lot of warmth from the heater while driving on the freeway, but now it takes a very long time to warm up.

During the test drive, the technician confirmed that the check engine light was indeed on, but they didn't notice any other concerns related to the customer. After a vehicle health inspection, the technician found no relevant issues. 

To investigate the check engine light, the technician did a vehicle code scan and P0116 code, which meant a problem with the engine coolant temperature. This was the lead to investigate the car heater problems.

With the customer's approval for additional diagnostics, the technician used a specialized scanner designed for this vehicle to verify the codes. They checked the live data of the vehicle and noticed that the engine temperature was not reaching the required level of 175° Fahrenheit.

To follow up on this, the technician used an infrared thermometer and found that the coolant temperature at the thermostat housing was reaching a maximum of 175°F.

Based on their findings, the technician recommended replacing the thermostat. After removing the thermostat, the technician found it in a stuck open position, even when it was cold. This confirmed that the faulty thermostat was the cause of the check engine light issue and why the heater wasn't warming up properly.

Does the issue look like this? if not accessible your shop will document it

Typical Fixes to Address the Cause(s)

The following chapters bases themselves on experiences from our auto repair shop; we'll describe related problems' causes and fixes.

"Heater core replacement" fixes "Restricted heater core"

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Hey, Why is My Car's Heater Not Working?
Sometimes a problem is more challenging to describe than it initially looked like. If you are not sure your problem is described by this article, please find below similar vehicle symptoms, which might describe better the issue you are experiencing.

Other things your auto repair shop might talk about:

Heater control valve. Cooling system. Cabin air filter. Coolant level. Radiator cap. blown fuse