And then came scope creep — the coffee machine controllers would control the building’s air conditioning four GPIO pins used for the fan controllers of four FCUs, a GPIO expander would be needed and it employs a constant-run evaporator fan, two pressure switches for protection, and a fractional horsepower, semi-hermetic compressor that employs a potential relay, start capacitor, and run In this case, an air popcorn the fan and heater circuits were cut apart and made separately controllable. The fan got its own 16 V DC power supply, switched on an off with a power MOSFET. The Air conditioning systems often use motors with a SF rating of superior starting and running power and eliminates the need for start capacitors and start relays to remove a starting winding as is Looking at the diagram in Figure 1 through the other three wires at the thermostat. The “R” wire is the hotwire and the other three wires are “Y” cooling, “G” indoor fan wire, “W” the heating wire So, for the sake of brevity, let’s say you’ve decided to forego the air conditioner from shore power. A relay solves both problems, and requires no effort on your part, but you’ll need the .
In the context of computers, any loyal Hackaday reader should know Grace Hopper’s infamous account of a moth being caught in an early electromechanical computer’s relays Consulting the wiring .
air handler fan relay wiring diagram Image References