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Summary
  • The heart of your vehicle’s system is its heater core, and the blower motor is like the lungs.
  • Heater hoses and heater pipe lines transport coolant from the engine to the heater coolant and then the radiator.
  • The HVAC heater blend door actuator directs the hot air while the HVAC heater control valve and heater valve control the flow of coolant.
  • Heater controls let you turn on the heater, adjust its settings, and turn it off.

The winter season is coming. Is your vehicle’s heating system ready for the approaching cold? Various parts in the heater portion of the heating, ventilation, and air conditioning (HVAC) work together to keep the temperature in the passenger cabin comfortable in all but the coldest weather. You must ensure that these heating system parts are working properly. If one of them fails, you’ll have to fix or repair the bad part.

Check These Heating System Parts For Winter

Heater Core

Think of the heater core as the beating heart of your vehicle’s heating system. It raises the temperature of the air flowing over it with heat drawn from hot coolant fluid. A faulty heater core can affect the entire heating system, leading to issues like insufficient heating, overheating, and burning smells. You often need to replace a failed core.

, Heating System Parts

Pro Tips are nuggets of information direct from ASE-certified automobile technicians working with CarParts.com, which may include unique, personal insights based on their years of experience working in the automotive industry. These can help you make more informed decisions about your car.

Pro Tip: The heater core can clog internally with rust or externally with dust and leaves.

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Blower Motor

The blower motor is a fan that gathers air from outside the car (norm) or inside the car (recirc/max) and forces air through the heating and the cooling unit of the HVAC system.

If you’re running the heater, the motor blows air over the heater core. The warmed air enters the passenger cabin, raising the temperature and fighting off the cold.

, Heating System Parts

Pro Tips are nuggets of information direct from ASE-certified automobile technicians working with CarParts.com, which may include unique, personal insights based on their years of experience working in the automotive industry. These can help you make more informed decisions about your car.

Pro Tip: All the air always goes through the evaporator core, but the blend door allows that dehumidified air to pass through the heater core when you turn your knob to the warm side of the dial.

A bad blower motor will show symptoms like strange noises, excessively weak or strong air currents from the vents, and burning smells. You’ll have to replace the problematic motor, preferably before it fails.

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Heater Hose

Heater hoses carry coolant fluid between the engine and the heating system. One hose carries hot coolant to the heater core, which uses the heat to warm the air moved by the blower motor. The other heater hose conveys the fluid back to the radiator for cooling.

The hot confines of the engine dry out the rubber that makes up heater hoses. A degraded hose can come loose or leak, releasing coolant into the engine bay. Replace the faulty heater hose immediately before the coolant leak damages a critical engine part.

, Heating System Parts

Pro Tips are nuggets of information direct from ASE-certified automobile technicians working with CarParts.com, which may include unique, personal insights based on their years of experience working in the automotive industry. These can help you make more informed decisions about your car.

Pro Tip: One of the heater core pipes will either have a restriction in it or it’ll be smaller. This is the one that leads into the heater core, while the unrestricted or larger hose leads out of the heater core. Hook these up backwards and the coolant being pumped through the heater core by the water pump can burst the heater core.

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Heater Pipe Line

Instead of heater hoses, some vehicles might use heater pipe lines to carry coolant from the engine to the heater core. Pipe lines are usually more rigid and stiffer than flexible rubber hoses. They generally last longer than hoses but can still leak coolant and loosen from their connections.

automotive heater pipe assembly
The heater pipe assembly shown in the photo is for a Nissan Pathfinder and includes a dedicated electric water pump for the heater core to get the best coolant flow possible. | Image Source: Richard McCuistian

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HVAC Heater Blend Door Actuator

The HVAC heater blend door actuator is a small motor that opens and closes the heater blend door that separates the heater and the rest of the HVAC system. It directs the heated air to the HVAC vents of your choice, enabling you to control the airflow and temperature in the cabin.

Most vehicles with a blend door-based heating system usually have a single HVAC heater blend door actuator. Some newer models with dual temperature controls have two actuators, one for the driver’s side and another for the passenger’s side.

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HVAC Heater Control Valve

automotive HVAC heater control valve
The HVAC heater control valve regulates the flow of hot coolant from the engine to the heater core. It often appears in vehicles that don’t use a blend door-type heating system but also may be found on vehicles that do use the blend door system. Some Ford Rangers are one example of this (see photo). This is the heater control valve for a 1998 Ford Ranger, which also uses a blend door even on the standard manual A/C/Heat system. | Image Source: Richard McCuistian

Also called the hot water valve, the HVAC heater control valve opens up to let more fluid flow into the heater. Since the water pump totally sends all the water through the heater core until the thermostat opens on most platforms, this heater control valve closes to allow that water to bypass the heater core and go straight back to the engine. This is why it has 4 water ports instead of 2.

This action raises the heater core’s temperature, warming the air passing over the part. When it’s time to reduce the temperature of the passenger cabin, the HVAC heater control valve closes, reducing or stopping the coolant flow to the heater core.

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Heater Valve

Like HVAC heater control valves, heater valves also control the flow of coolant to the heater core.

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Heater Control

You can’t adjust the passenger cabin’s temperature without an operational heater control interface. The heater control lets you adjust the air from the HVAC vents until the cabin is comfortably warm. While older vehicles have separate A/C and heater controls, newer models usually combine them into a single climate control unit.

On systems with electric door motors, installing a new control head may require a procedure to allow it to find both end stops on each motor before it will be ready to use.

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About The Authors
Written By Automotive and Tech Writers

The CarParts.com Research Team is composed of experienced automotive and tech writers working with (ASE)-certified automobile technicians and automotive journalists to bring up-to-date, helpful information to car owners in the US. Guided by CarParts.com's thorough editorial process, our team strives to produce guides and resources DIYers and casual car owners can trust.

Reviewed By Technical Reviewer at CarParts.com

Richard McCuistian has worked for nearly 50 years in the automotive field as a professional technician, an instructor, and a freelance automotive writer for Motor Age, ACtion magazine, Power Stroke Registry, and others. Richard is ASE certified for more than 30 years in 10 categories, including L1 Advanced Engine Performance and Light Vehicle Diesel.

Any information provided on this Website is for informational purposes only and is not intended to replace consultation with a professional mechanic. The accuracy and timeliness of the information may change from the time of publication.

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