HVAC System Components


HVAC Lexington systems provide heating, ventilation, and air conditioning for homes and businesses. They also help maintain optimal air quality by controlling moisture and eliminating pollutants.

When choosing an HVAC system, consider reputable brands that offer reliable and efficient products. Also, find a contractor to assess your home’s unique needs and recommend the right system.

The thermostat is the part of the system that senses indoor temperatures and signals the rest of the system to start heating or cooling as needed. It is usually mounted on an interior wall. It is important to locate it away from direct sunlight, heater vents, hot-water pipes, stairways or corners that affect the circulation of air. It is also preferable to install it near an electrical outlet so that it can be easily wired.

In older, mechanical thermostats (shown here), power comes into the unit through a transformer and flows over one or two wires to connect to the bimetallic strip. This strip is coiled and, as the temperature rises, bends outward. This causes electricity to flow through the circuit and trigger the furnace to start. The same occurs as the temperature falls. When the strip straightens out, electricity stops flowing and the heater switches off. The point at which the strip reaches its original shape depends on how warm or cold the room is. This is why a modern digital thermostat will often be able to stay on for longer than an old-fashioned mechanical one.

Modern thermostats are more flexible in how they control the temperature by using a microprocessor rather than a mercury switch. They use a sensor called a thermistor, which has an internal resistance that changes with temperature and the microprocessor converts this to a digital value. It then sends this information to the relays that control the fan and the heating or cooling system.

The thermistor in a newer digital thermostat can be replaced with another if it becomes damaged. The microprocessor in a digital thermostat also controls other features in addition to the setting and display of the current temperature. Most will show the time of day and have a clock and timer function. Some will even be able to connect with devices like light bulbs and sensors so that they can operate as home automation equipment.

The relays in a digital thermostat come from two different 24 volt transformers. The current from the one labeled RC energizes a terminal on the circuit board that connects to a ball-controlled mode switch. The switch is connected to a terminal marked G, which energizes the fan, and a terminal labeled Y, which energizes the cooling system.

Combustion Chamber

A combustion chamber transforms heat energy into mechanical energy by burning a mixture of air and fuel. The process is usually a gaseous combustion that creates carbon dioxide, water vapor and other byproducts. Those gases are then expelled from the engine. The combustion chamber’s design is a critical factor in the efficiency of an internal combustion engine. The goal of the combustion chamber designer is to achieve the desired mixture ignition and burnout at the specified operating conditions.

To accomplish this, the combustion chamber must have a structure that can handle the expansion of combustion gases and prevent the formation of carbon deposits on the piston or cylinder walls. It must also ensure that all of the gases in the combustion chamber are burned to completion without creating noxious fumes. The combustion chamber can be designed in different shapes and sizes to accommodate the needs of various types of engines.

Modern engines use a type of combustion chamber called an adiabatic combustion chamber. Its interior is lined with a refractory material that is durable enough to withstand the high temperatures of the combustion process. The refractory material is usually made from magnesia, chromium or stainless steel. The liners are supported by a rugged steel structure, which keeps them from melting or cracking under the pressure of hot combustion gases and other engine stresses.

In order to ignite the fuel mixture in the combustion chamber, a spark plug must be inserted into the plug hole at the top of the piston. The spark plug initiates the combustion reaction and heats the air to the point where it can expand and rise in temperature, which is then enough to support the flame. The resulting expansion of the air in the chamber pushes the piston down and forward to complete the combustion cycle.

The piston is connected to the crankshaft by a connecting rod that carries thermal energy from the piston into the engine’s rotary motion. The connecting rod must be mechanically strong because it is constantly subjected to stretching. It has a small end, which is secured to the piston, and a large end, which is connected to the crankshaft.

Evaporator Coil

The evaporator coil is located near the system fan inside your indoor air handler. It is usually in the shape of an ‘A’ and made from metals like copper, aluminium or steel because they are excellent heat conductors. It’s lined with coiled tubes that have fins for optimal heat absorption and cooling effect. Your HVAC system uses it as a heat exchanger for heating in the winter and cooling in the summer.

It’s important to keep the evaporator coil clean, as it’s where heat is absorbed. When it’s dirty, it takes longer to cool your home and consumes more energy than normal. It’s also an ideal location for the development of mildew, mold, and other microorganisms. When they get blown around the house through your vents, their spores can affect everyone’s health.

In a properly functioning HVAC system, the expansion valve meters the amount of refrigerant that passes into the distributor. Then it goes into the evaporator coil, where the liquid is converted into a gas by the heat it absorbs from the air. This gas then moves to the outdoor unit, where it changes back into a liquid and completes the cycle.

Your evaporator coil is an easy-to-maintain part of your air conditioning system. You can hose it down from the top with a garden hose during regular maintenance. It’s also a good idea to have it professionally cleaned at least once a year.

Like the compressor and condenser coil, the evaporator coil can develop tiny leaks over time. These are typically caused by the mixing of moisture from condensation with chemicals found in household air and can be fixed by a professional. It’s also a good idea, especially for older HVAC systems that use R-22 refrigerant (which depletes the ozone layer), to switch to a new unit that uses environmentally safe R410A. This will also reduce your energy bills and help to protect the environment.


The fan is an essential component of HVAC systems that circulates hot or cold air throughout a home. It is also a crucial part of dehumidification. The blower fan can be set to run continuously or to shut off once the thermostat reaches its target temperature. The continuous fan setting is more effective in multi-story homes prone to uneven temperatures, as well as humid climates that require extra dehumidification.

The ENERGY STAR rated fan uses less energy than other fans and is capable of operating at higher speeds. However, it is still necessary to clean and replace the filters regularly to keep the fan from overworking. This can cause the fan to overheat and trip the circuit breaker, requiring professional repair or replacement.

In heating mode, a fan that runs constantly allows you to benefit from more of the heat produced by the furnace. It can also reduce the stress on the system, lowering your energy costs and helping you avoid costly repairs. This is especially important in older homes with aging or inefficient heating systems.

Leaving the fan running in cooling mode can improve your indoor air quality by increasing the number of passes through the filter. This can lower allergies, asthma, and other respiratory symptoms. Moreover, if you use a high-quality filter, it can remove VOCs, bacteria, and viruses from the air.

Do HVAC Fans Bring in Outside Air?

In general, the blower fan does not bring in fresh outdoor air. It only moves the heated or cooled air that is already in your home to more evenly distribute it. However, some programmable and smart thermostats let you customize fan modes based on home conditions.

Keeping the fan in continuous mode may result in a slightly higher energy bill. But this may be offset by fewer stop-and-start cycles for the blower motor, which extends its lifespan. You may also need to change the filter more frequently than with the AUTO setting. Do not try to change the fan speed yourself, as doing so will void your warranty. This task is best left to professionals, who are familiar with how to do it safely and effectively.