Resetting Your Car's HVAC System

Introduction

Is the temperature or vent operation not working correctly for your car's air conditioner, defroster or heater? Do you hear strange noises form under the dashboard? This can be because the HVAC controller needs to be reset due to a procedural error or a simple "lock up" which can happen to any computer such as a laptop or desktop computer.

Let's Jump In!

Performing an air condition or heater system reboot is an easy job which most people can do. This procedure can fix problems such as strange noises, air vent management problems, temperature issues. This also should be done anytime repairs are made to the system such as a blend door actuator replacement or air conditioner compressor replacement. This will help the system recalibrate to maintain the system stability and correct functionality.

Supplies Needed

• Needle nose plies or fuse puller tool
• Fuse panel diagram or owners manual

If you do not have the fuse panel identification there is an alternative method that can be uses which is motioned further down in this guide.

Resetting the HVAC System

1. First, make sure the ignition switch or system is shut off. This will power down the HVAC system and begin the rebooting process, allow the car to sit for about 30 minutes.

2. Locate the interior fuse panel which should be under drivers or passengers side of dashboard in most cars, some fuse panels will be in the trunk as well.

3. Inside the fuse panel there will be one fuse labeled "HVAC system" or "AIRCON" each manufacturer labels their systems differently, this is why you need an identification label on the fuse panel or owners manual. If you do not have either of these, fear not, you can ask one of our experts, we are happy to help.

4. Once you have located the fuse, use a pair of needle nose pliers to remove the fuse.

5. Turn the ignition system on without starting the engine, allow the car to sit for about 5 minutes. This will tell the HVAC computer that the rebooting process has begun.

6. Turn the ignition system off and replace the HVAC system fuse.

7. Turn the car back on and start the engine, then power on the air conditioner and adjust the temperatures to the max settings, and do the same for both the defroster and heater. This will run through the "maximum" parameters for the vent position and temperature settings. You might hear noises as the process continues while calibrating which is normal.

Alternative Reset Methods

Using the following method can be used, but may not be as affective as the fuse removal procedure above. Please use gloves and safety glasses because you will be working with the battery. Always wash your hands afterwards and do not touch anything such as you skin, eyes, or clothing due to the residual battery acid that can be present.

1. Locate the battery of your car which will be under the hood in most cases. Make sure the engine and car are powered down and then disconnect the negative side of the battery, allow the car to sit for 5 minutes.

2. Reconnect the battery and start the car, the HVAC system will now start to go through the boot up (hard reset) process. Again, adjust the system to it maximum and minimum settings for each mode while the blower fan is set to the highest speed. This will help the temperature sensors realize an accurate reading for the HVAC computer to read.

3. Allow the HVAC system to run in each setting for approximately one minute to help set the "baseline", this will help stabilize the system readings so they can be recorded in controller memory.

4. For dual zone HVAC systems follow these steps for each side separately.

Final Steps

Now that the system has been reset, take the car for a drive while slowly adjusting the temperatures and vent modes to check performance. Also, adjust the blower fan speeds from high to low which will help test the temperature sensors feedback information to the computer fine-tuning the systems adjustments and you are all set.

Still Having Issues?

Because the HVAC system is computer controlled, there could be an electrical or mechanical failure which is causing the problem such as a bad blend door actuator which is super common. In this case it is best to perform a CAN scan (controller area network) which can tell you if you have bad module, sensor or blend door actuator. If you hear a ticking noise from under the dash that continues, and then stops, chances are the blend door actuator is bad and needs replacement.

Credits

This guide knowledge base was created by the 2CarPros Team, and by Ken Lavacot: Automobile repair shop owner and certified master automobile technician of over 30 years. If you have question or need help please ask one of our experts we are happy to help. Please visit our 2CarPros YouTube Channel.