Why is My Furnace Blowing Cold Air? Common Heating Issues


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The furnace makes the home warmer, but sometimes some problems arise. The furnace is blowing cold air doesn’t mean it isn’t working. It could be for a variety of reasons that this happens. The problem might be as simple as changing the filters or something more serious like a faulty thermostat or a broken blower motor. Before blindly ripping apart your furnace, you should diagnose the problem first to know what needs to be done and how much time it will take to fix it.

Why Is My Furnace Blowing Cold Air - Common Heating Issues

Reasons Why Your Furnace is Blowing Cold Air

1. The Sensor is Dirty or Disconnected

Sometimes this is possible, especially when your furnace has been in the same place for many years. The best thing to do is clean the sensor and reconnect it to ensure it works. It can be challenging to clean the sensor. If you have a good vacuum cleaner, go over it and clean it from the inside. If that does not work, you can use a bougie device to clean keyboards or even use a toothbrush to reach in between the grate and clean it out. If that still doesn’t work, replace the sensor.

2. The Thermostat or the Blower Motor is No Good

It is uncommon, but if your furnace keeps blowing cold air and the blower motor works fine, try replacing it. Unplug the furnace and remove the front shroud. It will expose the blower fan and power cord to be disconnected from the mainboard. To do this, you will need a vacuum with an appropriate nozzle that can be put inside and suck out all dust. Take a flat screwdriver and use it to pry the board out.

3. The Mainboard Has a Bad Connection

It might be because a screw got loose or the wire connector no longer holds tight. Check and repair this. You can do this by removing the electronics bay cover and then using an ohm meter to check if there is enough resistance in the part that is supposed to be connected to the computer. If unable to test, replace it with a new one.

4. The Blower Motor is Stuck

If the motor is stuck or jammed, it can cause the furnace to blow cold air. If you check for continuity in the blower circuit, you will find a problem in the capacitor as it draws too much current away from the motor windings. When this happens, there will be a lot of current draw at startup, and then once the motor finally spins up, it will draw way less current until after it reaches its average operating speed. When this happens, the motor will hardly run, and the blower will blow so little air that it can’t even make a dent in the temperature.

5. Air Filter is Restricting Airflow

It is the most common reason why your furnace is blowing cold air. If your filter becomes too clogged, it can restrict the airflow of your furnace. Most furnaces have filters that are easy to clean and replace. Just pull out the old one, remove any debris, and slide in a new filter or have a maintenance person do this for you.

6. Blocked Heating Coil

If your heating coils become clogged, this could cause cold air to be blown as the heat can’t rise to the ducts. The easiest way to check this is by looking inside your furnace and checking if it looks clean. You can try removing blockages yourself or hire someone to do it. You can also hire a cleaning service to do this for you.

There are many possible reasons why the furnace is blowing cold air, and the only way to fix this is by changing parts, so if you aren’t sure it is broken, replace it with a new one. You can consult a heating contractor (like the one here) for help if you need it. They can tell you which parts are faulty and where to buy them.


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