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Unit 61- Troubleshooting Electric Heat

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Neil Revollo
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Unit 61 Exam

Frage 1 von 15

1

Why is it important to cycle the furnace on and off several times when replacing a sequencer?

Wähle eine der folgenden:

  • It is important to make sure the heating elements and the blower are switching on and off in the correct cycle.

  • It is important to make sure the heating elements and the blower are turning on at the same time.

  • It is important to make sure the power is working correctly.

  • It is important to make sure that only the heating elements are coming on and not the blower.

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Frage 2 von 15

1

What could cause a false high reading for the supply-air temperature?

Wähle eine der folgenden:

  • If the temperature is taken with the blower on at the same time the heating elements are on.

  • If the temperature is taken after the unit has been running for too long.

  • If the temperature is taken with a probe inserted upside down.

  • If the probe is inserted in the supply plenum in a direct line of sight with the heating elements.

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Frage 3 von 15

1

If the furnace has one or more broken heating elements or one or more fusible links open, what should the technician do?

Wähle eine der folgenden:

  • The technician should check the furnace airflow.

  • The technician should check the power source to the furnace.

  • The technician should replace all the heating elements.

  • The technician should replace all the fusible links.

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Frage 4 von 15

1

The two general types of sequencers used on electric furnaces are

Wähle eine der folgenden:

  • High current sequencers and low current sequencers

  • Fast acting sequencers and slow acting sequencers

  • Mechanical and electronic

  • Individual time delay relays and all-in-one sequencers that control all the strips and the blower motor

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Frage 5 von 15

1

The most effective method of checking the heating elements of an electric furnace during operation is

Wähle eine der folgenden:

  • A visual inspection

  • Checking the Amp draw of each heat strip

  • Measuring the temperature of each heat strip

  • Checking the resistance of each heat strip

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Frage 6 von 15

1

What is the purpose of the white ceramic pieces on the strip heaters?

Wähle eine der folgenden:

  • They insulate the heater wire from the metal frame supporting it

  • They make it easier to identify where the heat strips are installed

  • They concentrate the heat of the strips

  • They seal the heat produced by the strips inside the furnace

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Frage 7 von 15

1

An electric furnace that runs continuously, regardless of the thermostat setting probably has

Wähle eine der folgenden:

  • An open strip heater

  • An open fusible link

  • A bad transformer

  • A stuck sequencer

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Frage 8 von 15

1

If a voltmeter shows a reading of 240 volts across the thermal limit to a strip heater on an electric furnace

Wähle eine der folgenden:

  • The limit is closed, breaking the circuit to the heater

  • The limit is open, breaking the circuit to the heater

  • The limit is open, completing the circuit to the heater

  • The limit is closed, completing the circuit to the heater

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Frage 9 von 15

1

Whenever a thermal limit or fusible link needs replacing, the technician should always check

Wähle eine der folgenden:

  • The power wire for voltage drop

  • The transformer control voltage

  • The thermostat calibration

  • The air filter and airflow

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Frage 10 von 15

1

Overheating can cause a terminal to discolor or the wiring insulation to melt. What should you consider when repairing the wire or the terminal?

Wähle eine der folgenden:

  • Replace the terminal end only. It is okay to cut off the end and repair the wire. If the terminal is on a relay, sequencer or fuse block, the component should also be replaced in addition to the wire.

  • Replace the terminal end only. It is okay to cut off the end and repair the wire. If the terminal is on a relay, sequencer or fuse block, only the wire needs to be replaced. The component does not need to be replaced.

  • It is recommended to replace the entire wire with another wire of the same or larger gauge. If the terminal is on a relay, sequencer, or fuse block, the component should also be replaced in addition to the wire.

  • It is recommended to replace the entire wire with another wire of the same or larger gauge. If the terminal is on a relay, sequencer, or fuse block, only the wire needs to be replaced. The component does not need to be replaced.

Erklärung

Frage 11 von 15

1

Given the following readings from an electric furnace, use the formula to calculate airflow.

CFM = (V x A x 3.412)/(∆T x 1.08)

What is the airflow in CFM and does this furnace have the recommended air flow?

Voltage at strips = 240 V
Amp draw of strips = 22.6 A
Return-air temperature = 65 ºF
Supply-air temperature = 120 ºF

Wähle eine der folgenden:

  • The airflow is 336 CFM; No, the air flow is too low.

  • The air flow is 312 CFM; No, the air flow is too low.

  • The air flow is 312 CFM; Yes, the air flow is at the recommended level.

  • The air flow is 336 CFM; Yes, the air flow is at the recommended level.

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Frage 12 von 15

1

A technician finds that a wire in an electric furnace is brittle and discolored from overheating. The technician should

Wähle eine der folgenden:

  • Cut off the overheated end, strip the remaining wire end, and reinstall it

  • Cut off the overheated end and splice on a short length of similar wire using high quality electrical tape

  • Replace the entire wire

  • Cut off the overheated end and add a short length of similar wire using a wire nut

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Frage 13 von 15

1

A technician takes the following readings while checking the operation of an electric furnace with 2 heat strips: 220 volts, 36 amps, 70ºF return air temperature, and 120ºF supply air temperature. What is the airflow through the furnace?

Wähle eine der folgenden:

  • (120 - 70) x 1.08 x 10 = 540 CFM

  • (220 x 36 x 3.41)/(120 - 70) = 27,002/50 = 540 CFM

  • (220 x 36)/(120 - 70) = 7,920/50 = 158 CFM

  • (220 x 36 x 3.41)/((120 - 70) x 1.08)) = 27,002/54 = 500 CFM

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Frage 14 von 15

1

When replacing a transformer, the technician should always check

Wähle eine der folgenden:

  • The 24 volt control circuit for shorts

  • The air filter and airflow

  • The temperature rise across the furnace

  • The continuity of the electric strip heaters

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Frage 15 von 15

1

What problems can be caused by overlubricating a blower motor?

Wähle eine der folgenden:

  • This could eventually cause the motor windings to short out.

  • The motor would run more effectively with the extra lubrication.

  • It is not possible to overlubricate the motor.

  • The blower motor could run faster than specifications recommend.

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