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TESTING CIRCUITS To troubleshoot an inoperative 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.
Figure 14-29(A).-Heat pump schematic.
Voltage Readings To begin, set your multimeter to voltage; ensure the power is on and all wires are connected to the component being tested. The four important troubleshooting procedures that apply to reading voltage are as follows: 1. Place the meter probes are on a path. If there is a voltage reading, the path is open. Place one meter probe on the left side of the CR contact and the other probe on the left side of the HP switch. If you obtain a voltage reading, this indicates that either the path is open or the contacts are open.
2. Place the meter probes on a path. If there is no-voltage reading, the path is closed. Place one meter probe on the left side of the CR contact and the other probe on the left side of the HP switch. If you obtain no voltage reading, the path is closed.
3. Place the meter probes across a load. If a voltage reading is obtained, the load is recieving current. When the load is NOT operating, you should check for a grounded winding and for winding resistance. Place one meter probe on the right side of the LLP switch and the other probe on the left side of IT. If you obtain a voltage reading, the compressor contactor is energized and the compressor should be running. 14-18(C)
4. Place the meter probes across a load. If there is no-voltage reading, you have an inoperative load. Replace the load. Place one meter probe on the right side of the LLP switch and the other probe on the left side of the IT. If there is no voltage reading, replace the load.
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