| Step | Expected Result/Action |
|---|---|
| 19. Turn power off. Use the capacitor discharge tool {Figure SP-8-6) to discharge any capacitors in the unit. Locate the wiring connected to the compressor motor windings. (Refer to the unit wiring diagram.) | The wiring related to the compressor motor is identified. All high-voltage capacitors used in the equipment are discharged. |
| 20. Measure the three-phase current as follows: Check the compressor and/or motor nameplate for full load amps (FLA). Set up a clamp-on ammeter to measure AC current on the highest range scale (higher than motor FLA). Place the damp-on ammeter around the wire connected to ihe T 1 terminal of the compressor as shown in Figure SP-9-20. Turn power on, then measure and record the current drawn by the T1 leg. Repeat the current measurement for the remaining two phases. One at a time, measure the current flow through the wires connected to the T2 and T3 terminals of the compressor motor. Calculate percent of current imbalance for a three-phase system using the formula below. % Imbalance = Maximum Current Deviation x , 00 Average Current | Current measured and recorded for the three legs. The percent current imbalance should be within 10%. (See the example calculation below.) If current imbalance exceeds 10%, look for an electrical terminal, contact, etc., that is loose or corroded and is causing a high resistance in the leg. Example of % current imbalance calculation Current measured T1 2 5 amps Current measured T2 2 7 amps Current measured T3 26 amps Average current 7 8 amps + 3 = 2 6 amps Difference between the average current and the measured current: T1 - 26 amps - 2 5 amps = 1 amp T2 = 2 7 amps - 26 amps - 1 amp T3 = 2 6 amps - 26 amps = 0 amp % Imbalances Maximum Current Deviation x Average Current % Imbalance x 700 = 3 . 8 % 26 Since the imbalance is less than 10%, the current balance between phases is acceptable. |
