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Carrier Furnace Blower Running After Startup—Quck And Easy Tips

Carrier Furnace Blower Running After Startup—Quck And Easy Tips

Have you ever encountered the frustrating scenario where your Carrier furnace powers up and the blower starts running, blowing cold air without initiating the ignition process? If you’ve experienced this issue and are uncertain about the reasons behind it or what steps to take, worry not. We’ve conducted extensive research to provide you with insights and potential remedies.

Understanding Code 12 On A Carrier Furnace

Carrier furnaces come equipped with various error codes and blinking light patterns that homeowners should be familiar with. Among these, error code 12 is one of the most commonly encountered issues.

Carrier Furnace Blower Running After Startup—Quck And Easy Tips

Error code 12 indicates that the blower immediately activates upon startup, pushing out cold air before the heating process begins. Normally, the blower should cease operation after about 90 seconds, unless you manually activate the furnace or adjust the thermostat settings.

In some cases, error code 12 can signify that the 120-volt AC power to the blower was interrupted during a power outage and needs time to cool down to prevent potential damage. If the blower continues running for more than three minutes, check your thermostat’s fan setting to ensure it is set to ‘auto’ rather than ‘on.’

Now that we’ve addressed error code 12, if you encounter a different error code or the furnace fails to ignite and produce heat, it’s time to explore other potential causes and their respective solutions.

Why Is My Furnace Fan Running But Not Producing Heat?

Let’s assume you’ve successfully resolved error code 12, but your furnace’s blower continues to operate without generating heat. In such cases, error code 33 may start flashing, indicating that the limit or flame roll-out switch has tripped and needs manual reset.

Here are some steps to diagnose and resolve this issue:

Carrier Furnace Blower Running After Startup—Quck And Easy Tips
  1. Filter Change and Duct System Clean-Up
    A clogged furnace filter and obstructed vents can hinder heat generation, making it the most common cause of this problem. Excessive dirt accumulation restricts airflow, leading to overheating and shutdown of the heat exchanger. As a result, your home remains chilly. If you notice the blower running without producing heat, consider replacing the filter with a new one and cleaning your vents and duct system to remove dust and debris. Your furnace’s user manual will provide guidance on filter replacement. Flat filters should be changed at least once a month, while pleated filters may last up to three months but should be inspected monthly for potential replacement. Always remember to power down the furnace and thermostat switches or perform a complete shutdown before changing filters or conducting general cleaning.
  2. Gas Supply Check
    If your Carrier furnace isn’t blowing hot air, it’s possible that you’ve run out of gas or the gas valve was accidentally turned off and not reopened. Check your gas gauge and contact your gas provider if the fuel level is low. Otherwise, trace your gas line starting from the furnace meter and ensure that the handle is positioned parallel to your gas pipe to allow gas flow.
  3. Faulty Control Board Inspection
    If the problem persists, inspect your control board and verify that the electrical connections are secure and free from interruptions using a voltage meter device. The control board contains relays that regulate voltage to each component in the furnace. If a relay controlling the blower motor becomes stuck in the closed position, it will continuously run. In such cases, it may be necessary to replace the control board. Another potential issue could be a malfunctioning starting capacitor in the furnace. Dealing with electronic problems can be challenging, so it’s advisable to seek professional assistance, though it may incur higher repair costs.

The Benefits Of Continuous Furnace Fan Operation

Running your furnace fan continuously can have several advantages. Furnace fans are designed to withstand continuous operation, so you need not worry about premature wear or breakdown. Here are some benefits:

  1. Improved Circulation of Heated and Cooled Air
  2. Prolonged Lifespan of the Furnace Unit
  3. Reduced Dust for Enhanced Air Quality
  4. Humidity Control during Cold Weather

Addressing Persistent Furnace Fan Operation

When your furnace fan continues to run even when it shouldn’t, it’s essential to identify and resolve the issue. Common causes include:

  1. Faulty Thermostat Wiring
  2. Malfunctioning Fan Limit Switch
  3. Fan Limit Switch Set to Manual Override

While addressing faulty thermostat wiring and a malfunctioning fan limit switch typically requires professional intervention, you can quickly resolve the issue if the fan limit switch is set to manual override by locating the switch and returning it to the automatic mode.

Locating The Fan Limit Switch

The fan limit switch is a crucial component responsible for controlling the furnace blower fan’s operation. It ensures the fan turns on and off at the appropriate times, aligning with the thermostat’s heating requirements. Moreover, the fan limit switch serves as a safety feature, preventing the furnace from overheating.

Carrier Furnace Blower Running After Startup—Quck And Easy Tips

This switch is usually located near the upper right corner inside the furnace panel cover. However, its exact location may vary depending on your furnace model and whether it is gas-fired or oil-fired. The switch is typically encased in a silver or white cover.


In summary, encountering error code 12 when starting your Carrier furnace is a normal occurrence, signaling that the blower will run for approximately 90 seconds. However, if the blower continues running beyond this period or another error code appears, it’s crucial to explore other potential issues. Understanding these error codes and their corresponding actions can help you address furnace-related problems effectively. For complex electronic issues, it’s advisable to seek professional assistance from a technician.

Carrier Furnace Blower Running After Startup—Quck And Easy Tips

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