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How the conditioned air gets into your car

Inside your vehicle, beneath the instrument panel, there is a unit referred to by different names depending on the vehicle manufacturer, but often referred to by the generic names “the plenum assembly” or “the case/duct assembly.”

This unit contains a number of different components which are used to control the air routing and distribution inside the vehicle, based on the selected control panel settings. It usually also contains the parts used to control the temperature of the discharge air. The heater core and evaporator are usually contained within this assembly. If the vehicle is equipped with a cabin air filter, most of the time it also will be located in the plenum/case/duct assembly.
Inside the case/duct assembly are doors or flappers which can change position to either expose or block airflow to and from various passages inside the case. These passages carry the forced air from the blower fan to either the dash outlet vents, floor outlet(s), the windshield defrost outlet(s), or a combination of these. The doors may be moved by simple cables, devices called vacuum motors (which use vacuum generated by the engine to cause movement), or small electric motors.
Do you ever need to vent?
 COOL TIP: Before driving off make sure all your vents are open and positioned properly to provide you with the optimum comfort you seek from your car’s air conditioning system. Prevent distracted driving syndrome and save yourself an accident by handling vents before you’re in traffic!
When having your mobile A/C system professionally serviced, insist on proper repair procedures and quality replacement parts. Insist on recovery and recycling so that refrigerant can be reused and not released into the atmosphere.
You can E-mail us at or visit to find a Mobile Air Conditioning Society repair shop in your area. Visit to find out more about your car’s mobile A/C and engine cooling system.

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