Diagnose and Fix
If the car AC blows cold air on one side and hot on the other, there are a few different causes but it’s likely the blend door actuator, also known as the temperature blend door actuator or vent mode door actuator. We’ll cover what can cause your car’s AC to only blow hot or cold on one side, what other symptoms you might hear, and how to diagnose the blend door actuator if you think it’s the cause.
Signs of a Temperature Problem in Your Car
AC Blows Cold Air One Side and Hot Air on the Other
There are a few different reasons why the AC might not work in your car. If the air conditioning in your car is blowing hot air on one side and cold air on the other, there could be a simple fix like adjusting the temperature or it could be time to replace a part like the temperature blend door actuator.
AC Blows Hot or Cold Air on One Side with Clicking Sound
If you experience the symptom of the AC blowing hot or cold air on one side but not the other and it’s accompanied by a clicking or ticking sound from the dashboard, it probably means a gear in the temperature blend door actuator is faulty and the actuator needs to be replaced.
Why the AC Blows Cold on One Side and Hot on the Other
Problems with the HVAC control module can be further diagnosed with an advanced scan tool, but here are some common reasons why the AC might be blowing hot and cold air on either side despite the set temperature settings.
Temperature Settings Adjusted Differently for the Passenger and Driver Side
Sometimes the AC blows cold on one side and hot on the other because the settings are set that way. This can be remedied by adjusting the temp on the cold side or vice versa to the preferred degree.
HVAC (Heating, Ventilation, and Air Conditioning) Control Module Program Needs a Reset
After disconnecting the battery, sometimes you can interrupt the HVAC (heating, ventilation, and air conditioning) control module’s program that conducts a self-test to find the blend door actuator’s location. If this happens, the module might read inaccurate data, leading to an inaccurate temp and requiring recalibration.
If the program needs to be recalibrated, sometimes it can be reset by disconnecting the negative terminal on the battery for about 5 minutes. After this, turn the key on and do not touch any HVAC controls. Hopefully this will reset the module.
Faulty Blend Door Actuator
The blend door actuator, also known as the temperature blend door actuator or vent mode door actuator, can break or malfunction over time. A blend door actuator is faulty if the HVAC control module commands it to a certain position but it fails to comply, leading to situations like the temp blowing hotter or colder than its intended setting. A faulty blend door actuator can be identified with an advanced scan tool and sometimes makes a clicking noise from the dash due to worn or broken internal parts.
Mechanical Problem with Vent Door
Sometimes the temperature will blow hotter or colder on one side from mechanical problems with the vent door or blend door inside of the heater box. The heater box is located below the dash and houses parts like the blower motor, heater core, and evap core. When you turn the heat or AC on, the blend door inside of the heater box will direct airflow from the blower motor. This is how hot air enters the cabin, and when the heat is turned on, air will flow from the heater core. Sometimes the blend door can jamb or stick, or have issues being controlled and cause problems with airflow like the ac blowing hot on one side and not the other or the heat to not work.
You can tell if there’s a problem with the blend door once the blend door actuator, which controls the blend door, is removed. A twist-knob will move the blend door. The knob should shift and stop, and you may hear the blend door open and close as you turn the knob. If the knob is loose and can be pulled in and out or twists too freely, like 360 degrees, there is likely an issue with the blend door.
To replace the blend door, steps like removing parts of the interior, like the dash, are common, and it can be time consuming to access and remove the heater box to replace this part. Parts like the heater core and AC evaporator core will need to be disconnected. The evaporator core, for example, will need the refrigerant to be removed by a professional before it can be safely disconnected.
Temperature Sensor Not Working
If the temp sensor isn’t working and the vehicle has a hard time picking up accurate information, this can affect the way the temperature settings work.
Head Unit or HVAC Controls Not Working
Sometimes the head unit or heat and A/C controls cause the A/C to blow hot or cold air on one side. Commands may work intermittently or not at all, making it difficult to control the temperature settings.
How to Diagnose Blend Door Actuators
Blend door actuators are the most common reason for the car air conditioning to blow cold air on one side and hot air on the other. They can be diagnosed with an advanced scan tool. The scan tool can tell if the blend door actuator should be in a different position than commanded. If it does not move with the adjustments and commands, there is a problem with the blend door actuator and it will need to be replaced. If the actuator is clicking, this is another sign it will probably need to be replaced.
Where Is the Blend Door Actuator Located?
The actuator is usually screwed in with an electrical connector on the corresponding driver or passenger side. Sometimes they are placed above or below the heater box, also known as the HVAC box.
How to Replace the Blend Door Actuator Yourself
Replacing the door lock actuator can be an easy repair. These are the steps to replace a blend door actuator on a 00-03 Chevy Monte Carlo
- Remove the Glove Box
- Remove the Temperature Door Actuator
- Disconnect the temperature door actuator wiring harness
- Remove the two 7/32 inch bolts from the actuator
- Pull off the actuator
- Install the Temperature Door Actuator
- Line up the shaft with the new actuator
- Push the actuator into place
- Insert the two 7/32 inch bolts into the actuator
- Connect the actuator wiring harness
- Test the actuator by moving the temperature control and watching the actuator
- Install the Glove Box
How-to Videos with More DIY Repairs to Fix Your Car
Check out this video to see the replacement on an 08-12 Ford Escape. To find videos specific to your year, make, and model, search 1A Auto’s how-to videos.
Shop Parts and Tools Mentioned in This Article
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- How to Use an OBD2 Scan Tool (Car Tester)
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- Is Your Car Heater Not Blowing Air?