Electrical Theory an Application for HVACR

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Chapter 6: Troubleshooting

Electrical Theory & Applications for HVACR

AMMETERS

Ammeters are used to measure the actual amount of current flowing in a circuit. This allows us to

determine whether a power consuming device is actually operaƟng. The example in Figure 6‐8 shows

the heaƟng elements in an electric furnace. The elements are sequenced so that they are energized

one at a Ɵme. By connecƟng a clamp‐on ammeter, a technician can see the current increase as each

element is energized.

Since each element has a raƟng of 5,000 waƩs, the amp draw of each element can be calculated using

Ohm’s law.

I = P / E

I = 5000 / 240

I = 20.8 amperes

Fig. 6‐6: Three ohmmeter readings are required to locate the common terminal.

Fig. 6‐7: Using an ohmmeter to check or “ring out” motor windings.