Car Heater Blowing Cold Air? Check the Blend Door Actuator

Updated: Dec. 22, 2022

As long as your engine is running, there's heat to be had. Try recalibrating the heating system or replacing the blend door actuator if there isn't heat.

blend-door-actuatorFamily Handyman
Does your car heater just blow cold air when you turn on the fan? It might be as simple as recalibrating the heating system or replacing the actuator. We'll show you how.

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Why is my car heater blowing cold air? Find the blend door actuator

blend door actuator

Heater blows cold air? Locate the blend door actuator

Where is the blend door actuator located? Remove the glove box and under-dash trim panels to find and replace the door actuator.

Also, find out why your furnace is blowing cold air.

blend door actuator

Test the door shaft

Remove the screws and lift off the blend door actuator. Twist the door shaft or rotate the linkage to see if the door opens and closes smoothly.

Car not blowing hot air?

Most late-model cars use electric motors (called actuators) to change the air temperature and direction of the airflow by opening and closing flaps in the heater box under the dash. If your battery has gone dead, or you’ve disconnected it to work on your vehicle and now you can’t change the air temperature, you probably just need to perform a recalibration.

Find the procedure in a shop manual (at auto parts stores for about $20). But if your car heater blows cold air and you’ve checked both heater core hoses to make sure they’re hot, you likely have a bum blend door actuator. You can usually diagnose and fix the problem yourself in about an hour. A new door actuator costs less than $100. All you need is a shop manual, a 1/4-in.-drive socket set and screwdrivers. Here’s how.

Consult the repair manual to identify which actuators control the defrost-vent-floor “mode door” and the temperature-regulating “blend door.” Then peer under the dash and locate the suspect actuator on the heater box. Have a friend switch between modes or temperatures while you watch the actuator. If the actuator doesn’t move, it’s probably bad.

There’s a chance the mode or blend door actuator may be good but the door or linkage is binding, so check it before you replace the actuator (photo above). If the door binds, take it to a pro for replacement. However, if it moves smoothly, buy a new blend door actuator from the dealer or auto parts store. Install it and test the operation. In some cases, you’ll have to perform a calibration.

Required Tools for this Project

Have the necessary tools for this DIY project lined up before you start—you’ll save time and frustration.

  • Socket/ratchet set
You’ll also need a flat-blade screwdriver and a Philips-head screwdriver.