How Your HVAC System Works (and Could Break Down)

Understanding the basics of how your heating and cooling systems work can help you catch problems and know when it’s time to get your systems serviced. With this simple guide to the mechanics of common HVAC equipment, you can understand where to look when something goes wrong.


There are several different ways to heat your home, but the vast majority of folks use a gas furnace. Here’s how the main components of this system work together to maintain ideal temperatures in your home:

  • Gas (Fuel) Valve: If you have a furnace running on natural gas, you rely on the gas valve to provide the fuel to burn to create heat. If you’re having issues getting the furnace to turn on or even shut off, this valve can make it difficult or dangerous to run the furnace.

  • Heat Exchanger: This part of the furnace heats the cooler return air that enters thru the system for heating, so it can be circulated through the home. A cracked or faulty heat exchanger won’t heat as well if at all and can be a carbon monoxide safety hazard. If you notice cracks on the external part of your furnace, find soot buildup in your furnace, unusual smells in your home, or even flames rolling out the front of your furnace, these could all be signs of a cracked or faulty heat exchanger and you should immediately shut off your system and contact a professional as soon as possible.

  • Blower: Once air has been heated (or had its heat removed, in the case of air conditioning), the blower pushes it into the ductwork so you can feel it. If the blower motor is making strange noises, you should seek the help of a professional because the entire system is likely to stop functioning properly.

  • Air Filter: All air coming through the system goes through the air filter. The filters pull out dust, dirt, and allergens that could lower your indoor air quality. Clogged air filters make it more difficult to push the air through, which might lower your home’s ability to warm or cool the air.


Air conditioning relies on a four-step system. Unlike heating, air conditioning does not actually cool the air. Instead, it uses refrigerant to pull heat and humidity out of the indoor air, so that the blower can circulate cooler air at the end of the process. These four parts each have an important role to play:

  • Compressor: The compressor uses a motor and pump to turn liquid refrigerant into a high-pressure gas and pumps it through the system to carry and transport heat. If the motor starts to wear out, you’ll get inefficient cooling, or possibly no cooling at all.

  • Condenser: The condenser allows that gas to release the heat collected inside the home. As the heat gets pushed out of the exterior air conditioning unit, the condenser turns the refrigerant gas back into a liquid. Dirty condensing coils, a common problem, make it harder to cool down the refrigerant.

  • Expansion Valve: After the condenser has done its job, the expansion valve changes the pressure of the liquid from high to low. If your AC system is blowing warm air or if there is frost coming from the vents, this may mean your valve has issues and the whole system may become less effective.

  • Evaporator: The evaporator coil is where the real cooling magic happens. It passes the refrigerant through a coil where the warm air blows over it. This causes the air to lose its heat and humidity. If you notice that your coils are frozen or covered in frost, the coil won’t be able to regulate cooling, which makes the whole system work harder and longer.


Of course, none of these parts would have much use at all if you didn’t have a thermostat to turn them on or ductwork to carry the treated air through your home. Your thermostat doesn’t need too much maintenance, and smart thermostats are particularly easy to operate. On the other hand, ductwork is a complicated network that could be hiding all kinds of problems. Leaks and kinks in your ducts can prevent you from feeling the treated air at all--a problem usually solved by duct sealing. If you’re having major problems with your heating or air conditioning, it is best to get advice from a professional.

Like everything else in your home, it’s valuable to have some understanding of how your furnace and air conditioner work—you'll have a better chance of identifying issues and taking the appropriate steps to address them. Unfortunately, some problems are unavoidable. For prompt inspection of your heating or cooling systems, schedule an appointment with Coolray today or call us at 770-884-7398. We’re here to help!

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