Why is my furnace blowing cold air?

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Winter can be a real gut-check with its cold, blustery wind, rush-hour snow storms and some downright frigid nights. It can also be a great time to hunker down on the couch, grab a blanket and enjoy the warm, soothing comfort coming from your heat registers.

But what happens if you settle in only to find – gasp – cool air blowing from the register? Don’t panic yet. Cool air from your heat vents doesn’t always mean you have to make a late-night call to your local Carrier HVAC contractor. There are a number of perfectly normal explanations that you can remedy yourself.

Check the thermostat

First, take a look at the brain of your comfort system – the thermostat – and check for the following:

  • Make sure it is set for heating, and not for cooling.
  • Check the fan setting. The “on” setting circulates air continuously whether it’s been heated or not. Change it to “auto” so it only blows warm air into your home.
  • Compare the temperature setting to the actual temperature in the home. You may need to turn up the set temperature for more heating comfort.
  • If you have a programmable thermostat, review temperature settings and make sure they still line up with when you are home or away from home.

Check the furnace filter

Check your filter and if it’s dirty, replace it. In some cases, a clogged, dirty filter might restrict airflow enough to affect your comfort. Or in more extreme cases, an overly dirty filter can cause the furnace to overheat and shut down.

Signs that it’s time to call an HVAC contractor

Unfortunately, sometimes cool air from the register DOES mean an issue is lurking that your Carrier dealer will need to address. Knowing what to look for can help your HVAC contractor get to the issue – and the resolution – a little quicker.

  • Fan limit switch: A malfunctioning fan limit switch might cause the furnace blower to circulate cool air when the furnace isn’t heating, or shut it down completely
  • Flame sensor: If the temperature inside is cooler than the thermostat’s setting, or if the furnace turns on and off repeatedly, a flame sensor may be malfunctioning.
  • Leaking ducts: If air from the registers is cooler and/or weaker than usual, and you notice higher heating bills, your air ducts may be leaking.
  • Pilot light is out: If you have a pre-1990s furnace, a furnace blowing cool air or shutting down may indicate that the pilot light is out. Follow the manufacturer’s instructions to re-light.

If you do end up contacting your Carrier dealer, doing a little advanced troubleshooting might help make the process faster, more efficient, and maybe save a little time on the service call.

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