Category: HVAC Components

Thermostat

Thermostat

The thermostat is the command center for an HVAC system. The thermostat is what will switch the equipment on and off. Most people are familiar with the thermostat on the wall for their heating and cooling, but they’re in almost everything from water heaters to freezers and kitchen equipment.

Modern thermostats sense temperature using a thermistor. The thermistors resistance value changes depending on the surrounding temperature. A small microcontroller converts the measured resistance to temperature and decides based on desired settings if heating or cooling should be switched on. continue reading...

Condensate drains and traps

Condensate drains and traps

Improper condensate trapping can cause a lot of property damage. It’s necessary that a drain line is installed correctly to avoid damage to a residence or business.

Evaporators coils are installed to allow a blower to either push or pull air across the coil. The pressure, either positive or negative applied across the coil is also the same applied pressure to the drain line connected to the drain pan of the evaporator coil. continue reading...

Thermistor

Thermistor

Thermistors are used to sense/measure temperature. You will find them in ductless splits to detect evaporator coil or condenser temperature, temperature measuring devices such as a digital thermostat, ambient air temperature, PTC start relay, and supply or return air temperature. The name thermistor is a combination of “thermal” and “resistor.” continue reading...

Pressure switch

Pressure switch

The plastic orifice shown in the image above is a snubber. Sometimes the appliance will experience sudden pressure changes such as wind against the exhaust or the burners igniting. The snubber is designed to only allow a designed amount of pressure to be pulled against the switch at one time.

The insert should not be removed to make the appliance function. If you remove the insert and the appliance works, you have another larger problem such as a plugged intake, plugged exhaust or drain. continue reading...

Fan center control

Fan center control

Two different fan center controls

Fan center controls generally are found in older standard furnaces. These are added to separate the heating side from the air conditioning side and added while air conditioning is installed. Newer furnaces have everything controlled via the control board.

Older atmospheric furnace fans are controlled by temperature and a temperature-controlled fan won’t work for air conditioning since the fan needs to run as soon as air conditioning is triggered on. continue reading...

Igniter

Igniter

The igniter is what’s going to ignite the gas in the combustion chamber.

Two of the most common igniters are the silicon carbide and silicon nitride.

Silicon Carbide

Silicon carbide is among the older of the hot surface igniters. They come in different styles, and most of them run off 120v. They are very fragile and crack easily if not handled carefully. There’s a myth that the oils in your skin will cause damage. It’s not true. continue reading...

Burners

Burners

Inshot Burners

There are many different kinds of burners. We’re mainly going to focus on the inshot type burner as seen above. The inshot burners are in most modern furnaces. A combustion blower is used to pull the flames through the burner tubes into the heat exchanger.

Burners are used to prepare the air:gas mixture for combustion. Gas is shot through one side, and as gas flows through at a relatively high speed, it pulls primary air into the burners with it. The quick flow of gas pulling air in with it is called the venturi effect. continue reading...

Control board

Control board

Furnace control boards can be very intimidating for newer technicians without much experience working with them. They’ll typically have many wires running to/from them, flashy lights, bulky built-in relays, resistors, and capacitors. It all looks very confusing, but it’s really not.

Ignition control boards

Ignition control boards are typical in older systems. They control the gas valve, igniter, flame sensor, and the damper (when used). With a call for heat, the board will start the sparker and light the pilot. When it senses the pilot, it will continue to light the burners. continue reading...

Flame roll-out

Flame roll-out

The side facing outside furnace / the side facing inside of the furnace

Flame rollout switches are mounted around your burners. They exist to sense when/if the flame were ever to pose a risk to the homeowner.

These are usually bimetal switches that warp when heated to break the heat cycle when they sense a flame rollout situation. They’re traditionally manually reset by pressing the button in the middle, although some use a heat-activated fuse which would mean you’d need to replace the whole part if it were ever to sense rollout. continue reading...

High-limit

High-limit

Above images are two of the more common high limits found in residential and lite commercial furnaces

A high-limit switch is a bi-metal snap disc switch that warps when heated to break a heat cycle and used to protect the heat exchanger from overheating and burning out due to insufficient indoor air passing over it. A dirty filter or squirrel cage, undersized ductwork, or many supply air vents closed are among some of the reasons to set this switch off. continue reading...