ABSTRACT
End devices are devices that play a critical part in the control of mechanical systems. This chapter explores the various end devices that we encounter in every day life in the HVAC. A relay is basically an electrically operated switch. Rated for a specific coil voltage, the relay’s switch, or “contacts” change state when the proper voltage is applied to the “coil” of the relay. A relay with a single switch or set of contacts is referred to as a single pole relay. Relay logic, or ladder logic, is a method of using relays to accomplish some function or arrive at some outcome, given certain required conditions. Contactors are essentially relays whose contacts can handle much more power. Control valves are one of the most critical components of many, many HVAC systems.
