There are two basic types of circuits-load and control. The LOAD CIRCUIT consists of a circuit that contains a load and all of the wiring that provides line voltage directly to the load, such as compressor motor, fan motor, solenoid valves, lights, or any device that consumes current (other than the movement of an electrical switch). The second type of circuit is the CONTROL CIRCUIT. Simply stated, a control circuit contains controls that either open or close a path that operates a load device. Each load has a control circuit. Control circuits consist of thermostats, pressure switches, overload protectors, and all of the wiring in the control circuit.
Air-conditioning and refrigeration units normally have two fan motors and a compressor. Thesr components are considered load. A load is any device that consumes electrical energy. Most loads convert electrical energy into another type of energy to create some type of work. For example, electrical energy is converted to magnetism within a motor to make the motor run.
All loads have some type of control so they can be turned on, off, or regulated. These controls are located in a control circuit. The circuit is made up of controls and paths wiring. Controls and control circuits consume no electrical energy; they simply provide a path for electrical energy to flow, thus indirectly controlling the operation of various types of loads. Figure 14-29(A) shows an electrical schematic wiring diagram of a heat pump. At first glance the diagram appears complex, but after studying the diagram briefly and looking at one circuit at a time, the diagram becomes easy to follow and understand. An example is as follows: Look at the first circuit in figure 14-29(A). The circuit contains a control relay contact (CR), high-pressure switch (HP), liquid line pressure switch (LLP), compressor contactor (C), and an internal thermostat (IT). This is a complete circuit. The CR is simply a set of contacts and falls in the category of a path; the contacts are either open or closed. The HP and LLP are both pressure switches and are controls in this circuit; the pressure switches are either open or closed. The C is the compressor contactor. Actually this is a magnetic coil located within a contactor that simply closes all of the contacts in the diagram that are labeled C. The IT (internal thermostat) is located inside the compressor and opens when there is a temperature rise. The only load in this circuit is the compressor contactor because it is a current consuming device. Now, look at figure 14-29(A) and see if you can find the load in the second circuit. The load is the indoor fan motor (IFM) because it is a current consuming device. The IFR contact only provides a path for the current to energize the indoor fan motor.
To troubleshoot an in operative or improperly operating unit electrically, you must be able to use a process of elimination systematically and use a multimeter effectively. Remembering and understanding a few simple rules will enable you to use a multimeter to locate a faulty electrical component or control. The first circuit in figure 14-29(A) is used as an insert to illustrate the different meter readings you will encounter when troubleshooting an electrical system. Refer to the insert next to the applicable troubleshooting procedure.Continue Reading