Once the source of an electrical problem has been isolated to a malfunctioning load or control circuit (Service Procedure SP-7), the next step in the troubleshooting procedure is to find the faulty component in the circuit. This can be done by observing what load devices are working and not working in the equipment, then troubleshooting the circuit containing the load device that is not working. It is done by using a troubleshooting technique called hopscotching.
As shown in Figure SP-8-1, hopscotching involves making a series of voltage measurements across each component in the malfunctioning circuit. The measurements start from the line or control voltage side of the circuit and move toward the load device, such as a motor or a relay coil. Measurements are made until either no voltage is observed, or until the voltage has been measured across all the components in the circuit. As a result of making the voltage measurements, one of the conditions described below should be observed.
Open Component — A t some point within the circuit being tested, no voltage is indicated on the VOM/DMM. This pinpoints an open component or set of switch contacts between the last measurement point and the previous measurement point. Figure SP-8-1 shows an example of this situation, where the thermally-activated T C contacts are open, preventing the relay coil from energizing.
If the open is caused by a set of contactor or relay contacts, you must find out if the problem is because the related contactor or relay coil is not being energized or is bad. Figure SP-8-2 shows an example of this situation. The contacts (C ) in the load circuit are open, preventing the compressor (COMP) and outdoor fan motor (OFM) from running. These contacts close when the contactor coil (C ) in the control circuit is energized. Before assuming that the problem is caused by the open contacts, you must use the hopscotch method to troubleshoot the control circuit containing the related contactor coil to find out if the coil is energized or bad. For example, if the thermostat cooling contacts (T C ) are open as shown in Figure SP-8-2, the contactor coil (C ) will not energize.
Load Device is Defective — If voltage is observed at the contactor coil, motor, or other load device, and the device is not working, the load device is most likely bad. You should turn off the power to the unit, then disconnect the load from the circuit and test its resistance to confirm that it is bad. For example, in Figure SP-8-3, there is power to the motor but it is not running. The motor is probably bad in this case.
