When Your Furnace Starts Blowing Cool Air, Here’s What It Might Be

The only time a furnace should blow cold air is when the thermostat’s setting is on “on” instead of “auto.” The on setting will continue to run the fan after the heater stops heating, and eventually, the air will feel cool. However, if your furnace doesn’t have the setting to run continually (which some don’t), it’s usually a sign something’s wrong with the components, the wiring, or the circuitry.

An excessively dirty air filter will slow the airflow through the furnace, cutting down on the velocity of the air going through the ducts. It may feel cooler than normal, since the amount being delivered is compromised.

If your heating system ignites electronically and only the blower runs for a short time with no heat, you may have problems with the Hot Surface Ignition (HSI) component. Look for the reset button and reset it. If the system shuts off again, chances are you’ll need an HVAC technician to diagnose and replace this part.

Another situation involving electronic ignition systems could be the flame sensor, which usually requires professional assistance to diagnose and repair. The flame sensor must get hot before the system will allow gas to enter the burner, and it’s as significant a safety feature as a thermocouple is on a standing pilot heating system.

A problem could exist in the control panel, the wiring box that sits on the outside of the furnace. There could be a bad wire or a loose connection. If you’re comfortable with wiring, turn off the gas and the circuit breaker before attempting to work on it. There may be circuitry inside the control box that could be at fault, as well. Typically such a repair requires diagnostic equipment.

Like your car, more recent models might be able to display a code that tells the technician what the problem is. The codes might be found inside the owner’s manual or on the inside door to the system.

To learn more about a malfunctioning furnace, contact the pros at Balance Point Heating & Air Conditioning. We’ve provided HVAC services for Fort Collins homeowners for more than 15 years.

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