Quiz
Unit 61 Exam
Questions in this quiz (15)
1Why is it important to cycle the furnace on and off several times when replacing a sequencer?
- AIt is important to make sure the heating elements and the blower are switching on and off in the correct cycle.
- BIt is important to make sure the heating elements and the blower are turning on at the same time.
- CIt is important to make sure the power is working correctly.
- DIt is important to make sure that only the heating elements are coming on and not the blower.
2What could cause a false high reading for the supply-air temperature?
- AIf the temperature is taken with the blower on at the same time the heating elements are on.
- BIf the temperature is taken after the unit has been running for too long.
- CIf the temperature is taken with a probe inserted upside down.
- DIf the probe is inserted in the supply plenum in a direct line of sight with the heating elements.
3If the furnace has one or more broken heating elements or one or more fusible links open, what should the technician do?
- AThe technician should check the furnace airflow.
- BThe technician should check the power source to the furnace.
- CThe technician should replace all the heating elements.
- DThe technician should replace all the fusible links.
4The two general types of sequencers used on electric furnaces are
- AHigh current sequencers and low current sequencers
- BFast acting sequencers and slow acting sequencers
- CMechanical and electronic
- DIndividual time delay relays and all-in-one sequencers that control all the strips and the blower motor
5The most effective method of checking the heating elements of an electric furnace during operation is
- AA visual inspection
- BChecking the Amp draw of each heat strip
- CMeasuring the temperature of each heat strip
- DChecking the resistance of each heat strip
6What is the purpose of the white ceramic pieces on the strip heaters?
- AThey insulate the heater wire from the metal frame supporting it
- BThey make it easier to identify where the heat strips are installed
- CThey concentrate the heat of the strips
- DThey seal the heat produced by the strips inside the furnace
7An electric furnace that runs continuously, regardless of the thermostat setting probably has
- AAn open strip heater
- BAn open fusible link
- CA bad transformer
- DA stuck sequencer
8If a voltmeter shows a reading of 240 volts across the thermal limit to a strip heater on an electric furnace
- AThe limit is closed, breaking the circuit to the heater
- BThe limit is open, breaking the circuit to the heater
- CThe limit is open, completing the circuit to the heater
- DThe limit is closed, completing the circuit to the heater
9Whenever a thermal limit or fusible link needs replacing, the technician should always check
- AThe power wire for voltage drop
- BThe transformer control voltage
- CThe thermostat calibration
- DThe air filter and airflow
10Overheating can cause a terminal to discolor or the wiring insulation to melt. What should you consider when repairing the wire or the terminal?
- AReplace 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.
- BReplace 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.
- CIt 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.
- DIt 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.
11Given 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- AThe airflow is 336 CFM; No, the air flow is too low.
- BThe air flow is 312 CFM; No, the air flow is too low.
- CThe air flow is 312 CFM; Yes, the air flow is at the recommended level.
- DThe air flow is 336 CFM; Yes, the air flow is at the recommended level.
12A technician finds that a wire in an electric furnace is brittle and discolored from overheating. The technician should
- ACut off the overheated end, strip the remaining wire end, and reinstall it
- BCut off the overheated end and splice on a short length of similar wire using high quality electrical tape
- CReplace the entire wire
- DCut off the overheated end and add a short length of similar wire using a wire nut
13A 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?
- A(120 - 70) x 1.08 x 10 = 540 CFM
- B(220 x 36 x 3.41)/(120 - 70) = 27,002/50 = 540 CFM
- C(220 x 36)/(120 - 70) = 7,920/50 = 158 CFM
- D(220 x 36 x 3.41)/((120 - 70) x 1.08)) = 27,002/54 = 500 CFM
14When replacing a transformer, the technician should always check
- AThe 24 volt control circuit for shorts
- BThe air filter and airflow
- CThe temperature rise across the furnace
- DThe continuity of the electric strip heaters
15What problems can be caused by overlubricating a blower motor?
- AThis could eventually cause the motor windings to short out.
- BThe motor would run more effectively with the extra lubrication.
- CIt is not possible to overlubricate the motor.
- DThe blower motor could run faster than specifications recommend.
Information
- Description
- Unit 61- Troubleshooting Electric Heat
- Author
- Neil Revollo
- Language
- English
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