Electric Motor Control
10th Edition
ISBN: 9781133702818
Author: Herman
Publisher: CENGAGE L
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Textbook Question
Chapter 10, Problem 9SQ
Refer to the circuit shown in Figure 10–6. Assume that when the thermostat contact closes the compressor does not start, but the condenser fan and evaporator fan do start. When troubleshooting the circuit, a voltmeter connected across the compressor contactor coil CC indicates 0 volts. A voltmeter connected across the high-pressure switch indicates 0 volts, and a voltmeter placed across the thermostat contact indicates 0 volts. When the voltmeter is connected across the low-pressure switch it indicates 24 volts. Which of the following conditions could cause this problem?
a. The refrigerant pressure is too high.
b. The compressor contactor coil is open.
c. The refrigerant pressure is too low.
d. The thermostat contact is open.
Fig. 10–6 Pressure switches are often used in air-conditioning circuits.
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Chapter 10 Solutions
Electric Motor Control
Ch. 10 - Describe how pressure switches are connected to...Ch. 10 - What type of pressure switch is generally used to...Ch. 10 - A pressure switch is set to cut in at a pressure...Ch. 10 - A pressure switch is to be installed on a system...Ch. 10 - A pressure switch is to be installed in a circuit...Ch. 10 - Refer to the circuit shown in Figure 105. If the...Ch. 10 - Refer to the circuit shown in Figure 105. Assume...Ch. 10 - Refer to the circuit shown in Figure 106. Assume...Ch. 10 - Refer to the circuit shown in Figure 106. Assume...Ch. 10 - Refer to Figure 106. When the thermostat contact...
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- Refer to the circuit shown in Figure 105. If the pressure should become high enough for the pressure switch to close and stop the motor, is it possible to restart the motor before the pressure drops to a safe level?arrow_forwardRefer to the circuit shown in Figure 105. Assume that the motor is running and an overload occurs, which causes the OL contact to open and disconnect coil M to stop the motor. What effect does the opening of the overload contact have on the pressure switch circuit?arrow_forwardRefer to Figure 106. When the thermostat contact closes, the compressor and evaporator fan start but the condenser fan does not start. Which of the following could NOT cause this problem? a. The condenser fan motor is burned out. b. The coil of the CF contactor is open. c. One of the CF load contacts is defective. d. The CFOL contact is open. Fig. 106 Pressure switches are often used in air-conditioning circuits.arrow_forward
- A 230-volt, single-phase, hermetic compressor with an FLA of 21 and an LRA of 250 requires a disconnect switch with a rating of ___________ horsepower.arrow_forwardRefer to the circuit shown in Figure 106. Assume that when the thermostat contact closes nothing happens. Which of the following could NOT cause this condition? a. The high-pressure switch is open. b. The CCOL contact is open. c. The low-pressure switch is open. d. he coil of the compressor contactor is open. Fig. 106 Pressure switches are often used in air-conditioning circuits.arrow_forwardA single-phase electric motor is connected to a 240-volt, 30-ampere circuit. The motor nameplate indicates that the full-load current draw of the motor is 21 amperes. The motor is connected to an inertia load (a large flywheel) that requires several seconds for the motor to accelerate to full speed. Because of the long starting time, the motor causes the circuit breaker to trip before the load has reached full speed. Your job is to connect a resistor in series with the motor during the starting period that will limit the starting current to 90% of the circuit-breaker rating. An ammeter indicates that the motor has a current draw of 64 amperes when power is first applied to the motor. Determine the ohmic value and wattage rating of the resistor that should be connected in series with the motor during the starting period.arrow_forward
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