You push a few buttons or turn some knobs, and voila, you have warm air blowing on your feet or cool air chilling your face. How does all that happen? Well, it’s all thanks to the air blend box. This box lives behind your dash and serves up just the right temperature of air right where you want it.
Let’s break it down. First, there is the blower fan that circulates the air through the heating/air conditioning system. The fan can blow at different speeds, depending on how much hot or cold air you need to be comfortable. The blend box can either draw in fresh air from outside or recirculate air from inside the cabin. People often choose to recirculate air when first starting the vehicle until it starts to either cool down or warm-up.
The next thing the blend box does is direct airflow over the heater core to warm the air or over the air conditioner evaporator core to chill it – or a blend of hot and cold to get it just right. From there the blend box can direct the air out into the passenger compartment through the floor vents, the panel vents, the defroster, or a combination. All of this allows you to customize the climate just the way you like it.
Some vehicles have different climate control zones, like one for the driver and one for the passenger – or even more zones for the back seat. Additional blend boxes are used for this. Climate controls could be manually adjusted, or computer-controlled depending on your vehicle.
The blower motor and all the little actuator motors that open and close the various blend doors can fail and need to be replaced. Most new vehicles come with a cabin air filter. This filter cleans the air before it gets into the blend box. If you neglect to change the cabin air filter, it can get clogged, smelly, and even allow mildew and other microorganisms to build up in the blend box.
Your service center can perform a heating/air conditioning system cleaning service that will clean and disinfect the system, restoring a fresh clean scent. If you are not getting enough hot or cold air, your service center can inspect your system, diagnose the cause, and set things right. And don’t forget to replace your cabin air filter on schedule. If you live and drive in dusty conditions or where there is a lot of pollen or other pollutants, you may need to replace your cabin air filter more frequently.