Theory and troubleshooting using short modules packed with images to make learning quick and easy.
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…
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." A thermistor changes electrical resistance…
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…
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…
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…
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…
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…
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…
Above images are two of the more common high limits found in residential and lite commercial furnaces Overhead view with the supply air plenum removed so you can see into the furnace 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…
Thermocouple A thermocouple is a type of flame safety that prevents the gas valve from dispensing the gas into the burners without the presence of a flame. These are found mostly in older standard pilot appliances including (mostly older) furnaces, water heaters, and unit heaters. A typical thermocouple will produce upwards of about 30 millivolts.…