Expert Guide: How Your HVAC System Works

HVAC Tech checking a run capacitor on a condenser

When it comes to tackling an HVAC predicament, knowing how the system works is half the battle.

You probably invested a lot of money in purchasing and installing your heating and air conditioning system. Thus, you don’t have the luxury of making poor maintenance choices. Any so-called “experts” can over bill you and still leave the system broken. You need to stay informed to protect yourself from fraud. As you grow in your HVAC knowledge, you might even learn a few DIY techniques.

With that in mind, here a quick rundown of each component of your HVAC system to ultimately save you both time and money:

HVAC Air Return

Air Return

The starting point of the ventilation cycle begins with air return vents. The internal fan will start to suck air in through this vent, which pulls it through the filter, to finally pass it into the central system where it will be heated or cooled. One essential maintenance tip is to dust your returns regularly. Otherwise, dirt and debris in the returns will build up on your filters and congest the airways, which will strain the system and decrease the energy efficiency.


The filter is a thin sheet of fiber that slides below the main furnace. It’s designed to trap dust particles before leaving the building. You’ll find dozens of specific types available. Inspect and replace your filter monthly. You can solve some of the most critical HVAC issues by merely cleaning or replacing old filters. Poorly maintained filters not only weaken the energy efficiency of your entire unit but also significantly affect the quality of the air you breathe. Clogged air filters will pose a significant health hazard and possibly cause an asthma attack, irritate allergies, and even spawn deadly Legionnaires’ disease.

HVAC Air Filter
HVAC Exhaust Vents

Exhaust Outlets & Air Ducts

The exhaust outlets are the vents that release air to outside the building. Usually, this is done through the chimney or vents on the roof. If the outlets are clogged or otherwise broken, fumes may build up inside your home and risk a fire. At least once a year, you should sweep your chimney or dust your vent stacks. Especially during fall, leaves might easily fall on the roof and block the escape of hot air.

The duct system is a tube network that carries the filtered air from the furnace to each room of the house. HVAC professionals recommend you get your ducts cleaned every two to five years. However, extensive cleaning is not always necessary. If you still notice poor air quality after changing the filter, it may likely be the ductwork is cluttered with dust or has small holes that need patching. You can try several DIY options, though you risk injury to yourself and damaging the ductwork.

Electrical Elements

You should have a central electrical switch that operates the AC fan (probably located in your garage). Check if the wiring is faulty or if somehow the breaker is switched off. Then check the thermostat. It may need new batteries or a system reset.

HVAC Electrical Element
HVAC Condenser


Your condenser unit, otherwise known as the “box thing” outside, is the outdoor fan assembly that implements the air flow. You should ensure that no vegetation completely covers it. Leaves and natural debris can get sucked into the fan and damage it. During the winter month, it’s also possible the unit may suffer frost damage. You should plant shrubs around it to block the natural elements. You can even cover the condenser during winter with a breathable plywood stack. During spring, flooding may also damage the unit’s performance. Make sure to install the unit on an elevated platform or high terrain


Inside the condenser unit is a compressor that converts the warm outside gas to a liquid refrigerant. Then, it absorbs it through coils. Your thermostat will determine the rate the coils operate and thus the heating of the building. With many intricate pieces involved, the compressor is susceptible to failure, especially during severe winter seasons. If you suspect an issue in the compressor, call a professional.

HVAC Compressor
HVAC Coils


Also located in your condenser unit of the HVAC unit, the coils run the refrigerant and cools the air flow. However, if the coils are too cold, they may create ice and slow down or stop the rotation of the compressor entirely. You should never set your thermostat too close to freezing (around 55 degrees F). Keep it around the same temperature during the day as at night, since sudden changes can overwhelm the coils. If you suspect they are frozen over, you can pour warm water down the pipes. Otherwise, turn off the system and give it 24 hours to thaw.

Scroll to Top