Why Is My Furnace Blowing Cold Air? Reasons and Solutions

When the weather gets cold, proper heating keeps your family warm. Once you turn on the furnace, it heats the whole house. However, a furnace breakdown can lead to the furnace blowing cold air.

Don't wait. Call a professional HVAC company to examine and fix your furnace. Smooth Sailing Heating & Cooling provides expert Spartanburg AC repair services.

Why Is My Furnace Blowing Cold Air?

1. Check the Thermostat

The thermostat keeps your house comfortable, but these devices can malfunction. In some cases, you may have set your thermostat incorrectly, causing your furnace to blow cold air. To fix this problem, follow these steps.

Check or move the thermostat switch to the heat position. Next, check your thermostat settings and set them to auto. Doing so will turn on the heater and fan simultaneously.

If you installed a new thermostat, you could have issues due to bad wiring. Another possibility includes an incompatible thermostat and heating system. To get assistance with a thermostat issue, call an HVAC technician.

2. Wait 15 Minutes

The furnace has many complex moving parts that take time to work. As a result, when you turn on the furnace, the system can take some time to circulate warm air. If the air remains cold after 15 minutes, you have a system issue that a professional needs to fix.

3. Faulty Limit Switch

An inoperative limit switch prevents the thermostat from regulating the temperature. The limit switch turns on the blower once it reaches the desired temperature inside the furnace. If your furnace does not blow cold air, a technician will have to test the temperature probe inside your furnace.

4. Inspect the Air Filter

Clean air filters provide your home with clean and fresh air. A dirty air filter can result in your furnace blowing cold air. If the filter becomes too dirty, it can block the airflow over the furnace's heat exchanger.

The furnace can overheat, which can trip a high-limit switch that shuts down the system. This switch prevents further problems such as a fire or damaging components.

Start by removing your air filter and replacing the filter if it appears dirty. Most home improvement stores sell affordable air filters or call a reliable HVAC company for help.

5. Clean Oil Filters

Like air filters, an oil-fired furnace has filters that can become clogged. A dirty filter affects ignition, resulting in the furnace blowing cold air.

Depending on your skill level, you can clean or replace the filter yourself. However, the process can get messy, so you may want to leave it to the professionals.

6. Check the Pilot Light

If the furnace does not blow warm air, inspect the pilot light. Modern heaters do not have pilot lights, but most old systems do.

Pilot lights heat the furnace with a small blue flame. Without this light, the furnace cannot heat up.

Reignite the pilot light with a lighter to fix this problem. Even though this job seems simple, it’s safest for a professional to correct this issue.

7. Faulty Sensor

A faulty thermocouple can cause your furnace to blow cold air even after relighting the pilot. Thermocouple sensors control the furnace's gas valves and ignition. A technician will need to adjust or replace the sensor.

8. Overheating Furnace

An overheated furnace blows cold air as the system shuts down the processes required to start heating. These safety measures help prevent fires, carbon monoxide leaks, and explosions. The furnace can overheat for many reasons, including:

• Mechanical trouble: While the furnace runs, various parts and processes can malfunction. The most common problem caused by mechanical malfunctions includes overheating.
• Dirt and debris: Accumulated dirt can stop moving parts and other components from properly functioning. If this build-up continues, the furnace can overheat. Get your furnace professionally cleaned if it seems dirty.
• Furnace age: Old furnaces tend to overheat and break down easily. Consider buying a new furnace if you have one that constantly overheats. An older furnace will perform less efficiently and can suddenly stop working.

9. Leaking Air Ducts

Most HVAC systems have air ducts located throughout the home. Leaky air ducts can cause warm air to escape through gaps in the ductwork. If this happens, you need to contact a professional to find and seal the holes.

10. Clogged Drain Line

Some furnaces have a condensate line that drains the water away from the unit. When the condensate line gets clogged, the furnace will not ignite. As a result, it will blow cold air into your home.

To address the clog, perform a visual inspection of the drain line. Then, use a wet/dry vacuum to remove the debris.

11. Low Gas Supply

The furnace needs a steady supply of gas to operate. Insufficient gas will cause the furnace to turn off, resulting in cold air. A technician can examine the gas valve and pilot light for furnace repair.

12. Electronic Panel Issues

If your furnace has an electronic control panel, try resetting it. Switch the furnace's power off, restart the system, and check for warm air. If the problem persists, have a professional inspect your heating system.

13. Dirty Ignition Sensor

Modern furnaces do not rely on pilot lights for ignition. Instead, the heating process gets initiated by a flame detector. If the flame detector becomes dirty, the furnace will not ignite.

To resolve this problem, you need to clean the ignition sensor. However, it’s best to leave this job to a technician. Due to a lack of training and tools, you may injure yourself or damage your furnace.

Smooth Sailing Heating & Cooling: Have Us Take a Look

Homeowners can prevent a furnace blowing cold air with routine cleaning and maintenance. To avoid furnace problems, contact an HVAC professional today. Visit us to learn more about our heating installation services.

Need help fixing issues with a furnace? Contact Smooth Sailing Heating & Cooling today in Spartanburg, SC, to schedule an appointment. Call us at (864) 804-6400.