Electric Circuit Basics
You must understand the circuitry of the system you are installing or servicing to be an effective HVAC Technician. Before you can understand the complex circuitry of heating, air conditioning, and refrigeration systems, you must first understand the basics of electric circuits.
All electric circuits must have 3 elements to work properly, these elements are: Line, Switch, and Load.
Line - short for line voltage. AC power, 120 volts or 208/230 volts are the most common source of power for heating, cooling, and refrigeration systems.
Switch – the device which opens or closes the path for electrons to flow. While you are probably familiar with a light switch that you manually open or close. Heating, cooling, and refrigeration equipment uses switches that are controlled by temperature and pressure.
Load - a device which uses electrical energy to perform work. The most common device is an electric motor although, gas valves, and contactors are also examples of loads that you will often see. (These types of loads will be discussed in more detail later.)
In figure 1, you see the basic electrical circuit. In this instance, the switch is closed and the fan motor is running. This is called a closed circuit.
Figure 2 illustrates the same circuit with the switch open and the fan motor is not running. This is called a open circuit.
There are several different types of circuits but in with heating, air conditioning and refrigeration equipment most, if not all of the circuits you will find are series circuits. A series circuit is the simplest and easiest circuit to read, understand, and troubleshoot. A series circuit has only one path for current flowing through. All devices in a series circuit are connected end-to-end. Figure 3 shows a very basic series circuit. All switching devices in a series circuit must be closed for the load to receive power. If any one of the switching devices is open the load (motor) will not get power.
by Ron Walker
You must understand the circuitry of the system you are installing or servicing to be an effective HVAC Technician. Before you can understand the complex circuitry of heating, air conditioning, and refrigeration systems, you must first understand the basics of electric circuits.
All electric circuits must have 3 elements to work properly, these elements are: Line, Switch, and Load.
Line - short for line voltage. AC power, 120 volts or 208/230 volts are the most common source of power for heating, cooling, and refrigeration systems.
Switch – the device which opens or closes the path for electrons to flow. While you are probably familiar with a light switch that you manually open or close. Heating, cooling, and refrigeration equipment uses switches that are controlled by temperature and pressure.
Load - a device which uses electrical energy to perform work. The most common device is an electric motor although, gas valves, and contactors are also examples of loads that you will often see. (These types of loads will be discussed in more detail later.)
In figure 1, you see the basic electrical circuit. In this instance, the switch is closed and the fan motor is running. This is called a closed circuit.
Fig 1.
Figure 2 illustrates the same circuit with the switch open and the fan motor is not running. This is called a open circuit.
Fig. 2.
Series CircuitsThere are several different types of circuits but in with heating, air conditioning and refrigeration equipment most, if not all of the circuits you will find are series circuits. A series circuit is the simplest and easiest circuit to read, understand, and troubleshoot. A series circuit has only one path for current flowing through. All devices in a series circuit are connected end-to-end. Figure 3 shows a very basic series circuit. All switching devices in a series circuit must be closed for the load to receive power. If any one of the switching devices is open the load (motor) will not get power.
Fig. 3
Series circuits are used in the control of heating, air conditioning, and refrigeration equipment. With all of the components wired in series, or end-to-end, the opening of any switch or component will open the circuit and stop the electric load. The switches in a series control circuit are used to turn the load on or off based on temperature and/or pressure. Safety devices are designed to protect the equipment components should any unsafe operating condition occur; such as overheating or over pressure conditions.by Ron Walker