One of the frequent complaints that I hear from my customers when they are having a problem with their furnace is that it will run for a while, blow hot air, and then it will start to blow cold air for a several hours before coming back on and blowing warm air again.
Obviously, there are several possibilities and I will begin to check the individual components that are involved in the heating process. What I want to focus on primarily though, is how oftentimes I discover that the issue is connected to air flow, or actually the lack thereof. As I have mentioned in previous posts, dirty air filters cause many problems. Sometimes simply changing a dirty filter will solve an intermittent heating problem in a gas furnace. If not, I inspect the air conditioning coil that is located near the furnace. If that is dirty can also cause the furnace to shut down its production of heat yet still run and blow cold air.
What is happening is that your furnace is producing heat but the blower is not able to evacuate that heat away from the furnace compartment quickly enough because there is a constriction at the filter and/or in the evaporator coil because it is dirty. Because of lack of air flow the temperatures in the furnace rise above safe levels and the safety devices in the system shut the flame off. The blower continues to blow so that the moving air can remove the heat from the heat exchanger area and after a while temperatures drop and the furnace will reignite the flame and heat until temps rise too high again and the process starts all over again.
In this instance the issue can only be resolved by cleaning the evaporator coil and filter.
Obviously, there are other issues that can cause this, improperly installed inducer motor on a condensing furnace will also cause this, a malfunctioning control board, dirty flame sensor, the list goes on and on but the point I want to make is the importance of keeping your central heating system clean. Changing filters often is one of the most important things you as a homeowner can do to keep your system running efficiently and properly.
So, change your filters often and you should enjoy less visits from your local heating and air technician.
Take Care,
The HVAC Tech
For people who are eyeing to buy new furnace must consider reading this one. It will give them perspective to make their furnace safer and more efficient.
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