Theory and troubleshooting using short modules packed with images to make learning quick and easy.
Polarity is the direction of current flow in a circuit from the two poles, positive and negative. You require two points of differential charge for any electron movement to take place. In an AC circuit, each pole alternates between positive and negative 60 times per second. You can see from the image of the AC…
What is Direct Current? In a DC (direct current) circuit, all the electrons hop from electron to electron in a single direction, hence the name, direct current. Since electrons only flow in one direction, electrical polarity matters, so you'll need to place each wire exactly how it's depicted on a wiring diagram. Electrons flow from…
What is Alternating Current? Alternating current, (AC) is the most common form of electricity. AC became the standard due to the ease of distributing power over a long distance. With AC, a simple transformer outside your house steps the voltage down from the power company supply to a usable voltage in your home. Since it’s…
Everything is made up of atoms. Atoms are made up of protons, electrons, and neutrons. The nucleus of the atom contains neutrons which have a neutral charge and protons which have a positive charge. Electrons orbit the nucleus and have a negative charge. If you have the same amount of protons as electrons, you’d have…
Caution: It cannot be said enough how careful you need to be when drilling into a furnace to make pressure testing ports. Avoid drilling through the cabinet and hitting anything such as electrical, condensate traps, or the heat exchanger. Static pressure is the resistance air faces when moving through a duct system or the balloon…
Temperature rise is the difference of air temperature between the conditioned return air and the heated supply air sent from the furnace. Temperature rise is part of the initial setup of a furnace. Before taking a temperature rise reading, you will need to make sure you have a clean filter, proper gas pressure, combustion test,…
Relative humidity is the amount of water vapor in the air, expressed as a percentage, compared to the amount of water vapor it can hold at that temperature. As air is heated, it expands. With this expansion, the amount of moisture it can hold also increases as there’s more space for the water to be…
When our bodies overheat, it begins to sweat to reduce your core body temperature. Once the sweat is on your skin, it should evaporate which in turn will cool your body. However, when there’s more moisture in the air (high dew point) the sweat takes longer to evaporate and the warmer and more uncomfortable you…
The wet-bulb temperature is a measure of moisture evaporation. Basically how easy it is for moisture to evaporate. Wet-bulb is measured by an ordinary thermometer with a wet cloth on the end. You can also use a sling psychrometer or digital psychrometer as well. When the air passes through the wet cloth, moisture from the…
The dry-bulb temperature is also referred to as the air temperature or ambient air temperature. The dry-bulb temperature is not affected by the moisture in the air. It measures the sensible temperature of the air. It’s the temperature you’re usually referring to when you’re telling your friends how hot it is outside. The dry-bulb can…