6 Reasons & Solutions for Your Furnace Blowing Cold Air

Posted On: December 9, 2022

HVAC technician completing a furnace tune-up.In the dead of winter, there’s nothing quite like the instant relief of holding a cold hand over a vent blowing hot air. There’s also nothing like the disappointment of your furnace blowing cold air inside when it’s cold outside.

Before you panic because your trusty heater has picked a terrible time to go into hibernation, there are some legitimate reasons why normally functioning furnaces can give you the cold shoulder. Some of these you might be able to fix yourself to get the warm air flowing.

This is a blog post from Carrier, one of our trusted HVAC Brands.

Why Is My Carrier Furnace Blowing Cold Air?

If your furnace isn’t blowing hot air, there could be many things causing the problem, but one of the more common reasons is that your furnace is set to “on” instead of “auto.”

In this case, the fan will run constantly, even when the furnace isn’t heating. Resetting the thermostat to auto should resolve your issue if the system is working properly. Of course, more complicated issues often require furnace service. If you need help, you can call Short Pump Heating & Air to schedule a furnace repair.

Here, we’ll explore thermostat settings and other common causes for your furnace blowing cold air, and we’ll offer both DIY and professional solutions.

Incorrect Thermostat Settings

Symptoms: If a thermostat is set incorrectly, you might notice your furnace blowing cold air from the heat registers, a lower-than-expected temperature reading on the thermostat, or you may hear your AC running outside.

There are many options for thermostats — programmable models, smart thermostats, and more — but they all control both heating and cooling. With all these choices, there are several scenarios involving your thermostat that can result in your furnace blowing cold air.

Solution: If you notice any of these symptoms, the first step is to check the thermostat and look for obvious answers.

  • Is it set for cooling instead of heating? If it is, simply reset the thermostat to heat your home. Or reset it to auto. When it’s set to auto, it will automatically change between heating and cooling as temperatures change.
  • Is the fan set to run continuously? If so, your system may be circulating cool air between heating cycles. Changing the fan setting to “auto” will turn off the blower when the system isn’t actively heating and turn it on when it’s heating your home.
  • Check the temperature setting to make sure somebody else didn’t change it to a lower setting.
  • If you have a programmable thermostat, review your “comfort schedule” for any issues, and make sure your programmed settings haven’t shifted times due to daylight savings time.

Of course, if your thermostat isn’t working or the furnace has a mechanical issue, these adjustments likely won’t resolve the issue of your furnace blowing cold air.

If you’ve made some of the described adjustments and your system doesn’t respond, it may be time to contact your local Carrier HVAC technician for a professional analysis of your heating system.

The Heater Hasn’t Warmed Up Yet

Symptoms: You hear your furnace kick on, but there’s no airflow, or the heater is blowing cold air. While your first instinct might be to call your HVAC technician, your furnace might be operating normally.

Many furnace models include a fan limit switch that allows the furnace to warm up the air before the blower pushes it out through the air ducts and into your living areas.

Solution: Check the owner’s information for your furnace to see if there should be a blower delay after the gas burner kicks on. If, after a few minutes, the furnace is still blowing cold air, you may need to contact a Short Pump Heating & Air expert.

The Pilot Light Is Out

Symptoms: The furnace is blowing cold air, or there’s no heat in the house. Pilot lights used to be a standard component on gas furnaces before the 1990s. When the pilot light is out, you’ll find an otherwise perfectly functioning furnace blowing cold air.

Because a pilot light is designed to burn continuously, it also uses more of your gas supply, which can be reflected in higher utility bills. So, if you have an older model furnace, your home is too cold, and the furnace hasn’t turned on, your pilot light may be out.

Solution: Start by checking that your thermostat is set properly. Next, locate the pilot light assembly on your furnace and see if there’s a flame. If the pilot light is out, follow the manufacturer’s directions on how to relight it. If it won’t stay lit, it may be time to call a professional.

When your pilot light is damaged, your system won’t operate efficiently, if it runs at all. Sometimes the issue may be as simple as cleaning the pilot’s orifice or the flame sensor. Even if the pilot assembly needs to be replaced, it’s usually not an expensive repair.

Finally, if your furnace has a pilot light, it may be time to consider upgrading to a new, higher-efficiency pilotless gas furnace.

The Fan Limit Switch Has Malfunctioned

Symptoms: If your furnace isn’t blowing hot air or isn’t operating at all, a component called the fan limit switch or high limit switch may have malfunctioned. You may also see an error message on your thermostat or a blinking LED light on the furnace control board.

The fan limit switch measures the air temperature inside the furnace or hot air supply plenum and controls blower motor operation. If the fan limit switch malfunctions, the blower might continue to operate even when the furnace isn’t heating the air, resulting in your furnace blowing cold air from your registers. Or it may prevent the furnace from operating at all.

Solution: Check your air filter and clean or replace it if needed. A clogged filter can restrict airflow, causing the heat exchanger to get too hot, which triggers the fan limit switch to shut down the furnace. If cleaning or replacing the filter doesn’t solve the problem, it’s probably best to contact a professional.

A Dirty Air Filter Caused the Furnace To Overheat

Symptoms: If you notice the air temperature in your home is cooler than normal, if the airflow from your heat vents seems weaker than usual, and/or if you hear the furnace running for short periods of time before shutting down (short-cycling), you may have a dirty air filter.

Lack of filter maintenance can lead to a buildup of dirt, dust, and other airborne pollutants that can clog your air filter, restrict airflow, cause discomfort, or in more extreme cases, cause system failure.

Solution: Before checking your heater filter, be sure the thermostat is set for heating and that the temperature setting is correct. If you still suspect the problem is a dirty air filter, consult your owner’s manual for instructions on removing and cleaning or replacing your air filter.

If cleaning or replacing the filter doesn’t solve the problem, contact your local Carrier dealer for assistance.

If you notice any of these issues and need service, call Short Pump Heating & Air at 804-364-9040. We’ll schedule a service today.

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