If your fan only runs when your furnace is heating the air, then you’re much less likely to experience your furnace blowing cold air. When overheating, your furnace can trip a high limit switch , causing the furnace burners to shut off so that the heat exchanger does not crack. If your thermostat is set to "on" instead of "auto," it could be causing your furnace to blow cold air. It’s Just Been Switched On – Any furnace will blow cold air when it starts up, since it takes time for hot air to travel through the system and into your home. Let’s look at some of the solutions to this common furnace problem. But according to downstairs tenant the fan is not on. It has always done this. If this is the case, you'll first want to turn the gas valve that supplies the pilot light off. What do you think? By switching the thermostat to “auto,” the fan will only blow when the furnace is heating the air. Your furnace blowing cold air could be caused by hot air escaping through holes in the duct work that carries the heat throughout your building. If the gas is on, but the pilot won't light or stay lit, the pilot tube or orifice may be dirty. Is it possible one made an adjustment (or work around) that he should not have? I have an electric furnace that blow cold air sometimes. You might be suprised to learn that one of the most common residential HVAC issues is the thermostat. That may be a quick and easy fix. Your furnace clicks on and the blower motor is running, but the air coming from the vents is cold or cool instead of hot. Any help would be appreciated. In other words; no vacuum means no ignition, which may be why you are experiencing cold air when you're expecting hot. If your furnace is blowing cold air, or is not operating at all, a component called the fan limit switch may have malfunctioned. Since heat pumps produce air that’s below that, it can feel cold to you. The fan blows fine. Help! Let us know what you find as that will help others. Check for an air duct leak, particularly, leaks from cold areas such as an un-heated crawl space or basement into the return air duct system. Check to see if one of these troubleshooting tips fixes the issue. Furnace overheating can be the cause of your cold air dilemma. I like Dan Holohan's expression "Keep your hands in your pockets" - my mom used to make me sitOn my own hands. (No not recently.). It’s freezing outside, and all you want is to get in your car and turn on the heat. Or maybe the air starts off hot, then turns cool before the furnace shuts down. My tenant is angry and I want to fix this for him. Consult your users manual for directions on restoring the settings for your specific unit. Thermostat: A Furnace Blowing Cold Air Could be Due to Your Thermostat. If your furnace ran out of fuel, or was simply low on fuel, this could be your problem. Check the air filter. But still the same issue. Another cause may be that you have a faulty limit that is opening prematurely. It's blowing warm air at the moment. When the fan is on, the furnace will continue to blow, regardless of whether or not the air is being heated. This “hot then cold air” sequence happens over and over and your home isn’t warming up. Help, we have an up/down duplex with forced air natural gas, installed in 2010. Your body temperature is around 98.6°F (everyone’s body temperature is slightly different, but that’s the average). Seals breakdown, the constant pull of gravity, rodents, incorrect installation, and even age can play havoc when it comes to delivering hot air. Then, use a pipe cleaner or other small brush to remove any clogs within the supply tube. But if it doesn't light, or it won't stay lit, you'll want to check that gas is flowing to the pilot. Once it hits the set temperature I'm guessing the gas will cut off and the fan will continue blowing. When heat called for and fan comes on it blows cold air, then heat, then cold, then off. If this doesn't resolve your cold air problem it could be the themostat itself, but before calling a professional, we recommend trying the other troubleshooting suggestions first. If this doesn’t fix your problem, and your furnace is still not blowing hot air, you can move on to some of the other potential culprits. As soon as the furnace cycles back on the air will warm up again. Check the following two switches to make sure that the furnace blower fan is not simply set to run continuously: If you need to introduce outdoor air into a building for air quality reasons, consider an air to air heat exchange system to save on heating costs. Unfortunately, it isn't uncommon for an HSI to malfunction. In such cases, a safety control device known as the limit switch will shut off the burners. Limit switch is at off 100, on 125 off 150. More diagnostic details are at FURNACE FAN CYCLES DURING HEAT, Our 22 year old furnace just started having intermittent problems. At my request a few days ago the tenant with thermostat set the fan to be ON all the time -and assures me it's still on. If you only feel your furnace blowing cold air briefly, and the air is quickly replaced by warm air, this is the most likely explanation. If your furnace seems to be blowing cold air, it could be a problem with the ignition system. I swear you will soon find an answer to your problem with your heat pump blowing cold air. They may even need to run a static pressure test during their assessment. If it stays lit, you should be back in business. Continue reading at FAN LIMIT SWITCH TROUBLESHOOTING or select a topic from the closely-related articles below, or see the complete ARTICLE INDEX. We have no relationship with advertisers, products, or services discussed at this website. Can you say what we ought to check? The oil from your fingers can cause permanent damage to the part. One of the most common causes of a furnace blowing cold air is not actually a repair at all. Maybe the fan is malfunctioning. Possible Conclusion 1: It’s Not Blowing Cold Air. it resets and works properly. Your thermostat has a switch for your fan that can either be set to “on” or “auto.” If this switch is set to “on,” then … Here are 6 common reasons for a furnace blowing cold air, and what you should do about it: 1. All Rights Reserved. As a pilotless burner owner, you'll want to keep your fingers crossed that your issue isn't related to your burner's circuitry. Pilotless furnaces have been an energy-saving breakthrough for the home and commercial heating industries. Check that the air filter is clean and that the ductwork is not obstructed. Changing your filter is a good starting point, but if the problem persists we have other options for you to troubleshoot. This issue is often caused by the thermostat receiving false readings. At the time the furnace is blowing cold air, I see two slow green flashes followed by 2 quick red ones. When we shut it off, then restart(sometimes up to 5 times). When the air temperature reaches the setting you’ve chosen — let’s say 70 degrees — the furnace can take a break until the air drops below 70 again. This article describes what to check if the warm air heating blower fan delivers intermittent cold air into the occupied space, or if the furnace cycles between blowing warm air & cool or even cold air into the building. Gas forced air furnace is Lennox G16 24 years old, in good condition. But you might want to consider calling a professional HVAC service who has the knowledge, tools and experience to find and repair the problem. Either hot air from the duct is blowing on the thermostat, causing it to think the RV is warmer than it actually is, or cold air is blowing across the thermostat, resulting in a similar issue. I have a York Diamond 80 furnace. 2. 11. As an Amazon Associate we earn from qualifying purchases. Heating up air uses a lot of energy and is financially costly. According to the book the 2 red flashes means "Retries or recycles exceeded". So why does the downstairs get so cold when thermostat is 68 and way way too hot at 70? Or use the SEARCH BOX found below to Ask a Question or Search InspectApedia. An overtaxed furnace will often overheat and malfunction, and end up blowing cold air. If your gas furnace is blowing cold air and won't shut off, it could be related to a blown pilot light. When the furnace resumes heating, I see the normal flashes of 20 green followed by one red. They are available in electric, gas and oil models. 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