written test 3 Unit 19,20,36,38,40,41 Flashcards
A common practice in condensing units is to use a contactor with only one set of contact opening only one side the power to the unit. This is to
Provide off cycle heat to the compressor
Besides maintaining pressure on the contacts for current carrying capacity, the pressure Springs have a second important function. This is took
Help obtain equal contacts against the stationary contacts
When a contactor coil is energized, how much resistant should be measured between “L1” and terminal “T1”
Zero ohms
Technician “A” says that if you take your voltage reading from terminal “L1” to terminal “T1” on contactor whose coil is energized, you should read zero votls. Technician “B” says that contactors only have normally open contacts. Which of the following statement is correct?
technician A is correct. Technition B is incorrect
An inherent motor protector is a
Thermally activated device in motor winding
The service factor of an electric motor is determined by
Motors Reserve capacity
Standards for motor overload protection are set by
National Electric Code
a solder pot is part of a
Resettable circuit breaker
Which of the following overload device is not affected to ambient temperature
A solder pot
B. Magnetic
C. Bimetal
D. Time delay fuse
Magnetic
The locked rotor amperage, LRA, of a motor is typically five times higher than the full load amper
the motor and can be as high as seven times the FLA
a. True
b. False
True
A set of contacts are closed when the relay is energized. These contacts are classified as normally closed.
a. True
b. False
False
auxillary contacts are usually rated at a lower amperage than the contactor’s primary contacts.
a. True
b. False
True
Contactor contacts that are badly pitted ean cause the motor to burn out.
a. True
b. False
True
A sure sign of contact failure is discoloration on the contact surfaces
a. True
b. False
False
Bimetal and solder pot overload devices are thermally operated.
a. True
B false
True
The sun shining on a distribution panel has no effect on the breakers in the panel.
True
false
True
- Magnetic overload devices are the most accurate type of device for electrical protection.
a. True
b. False
True
- The best way to repair a defective relay is by replacement
A. True
B. False
True
The most common material used on the surface of contacts is Brass.
A. True
B. False
False
Unit 20
Most electrical problems with an electrical motor are _____, _____, and _____.
shorted windings; open windings or grounded windings
Unit 20
A technician needs to check a single-phase compressor. He labels the three terminals “A,” “B,” and “C” and takes resistance readings of the windings. He reads 10 ohms from “A” to “B,” infinity from “B” to “C,” and infinity from “C” to “A.” Identify the terminals.
I can’t identify because it has open windings (infinity for B to C & C to A)
Technician “A” says that a shorted winding will result in an increased current flow through the winding. Technician “B” says that if a motor is to be replaced, a motor with a lower horsepower rating should always be used. Which of the following statements is correct?
Technician A
An open winding in an electric motor means that _____.
A wire in the winding is broken
Technician “A” says that well check in the bindings of a compressor, a reading of 10 ohms or less from the common terminal 2 ground indicates the motor is okay. Technician “B” says that the resistance of the start winding should always be less than the resistance of the run whindng.
Technician A Is correct
If the resistance of the run winding decreases, the _____.
motor will draw too much current while it is running.
If a condenser fan motor grounds out, it will usually _____.
trips the circuit breaker and shuts off the unit.
a megger
measure very high resistance
If a motor hums but does not start, there is a potential problem _____.
All the above
The recommended way to discharge a capacitor is to _____.
Use a 20,000 ohms 5 watt resistor that has had insulated leads solders to it
The wiring and connectors that carry the power to a motor must be in good condition. When a connection becomes loose, oxidation of the copper wire occurs. The oxidation _____.
acts as an electrical resistance that causes a connection to heat more
What is the best method to repair a fractional horsepower motor that has bad bearing?
Replace the entire motor
If the cost of repairing the motor is close to the cost of replacing the motor, it would definitely pay to repair the motor if the new components carries a one-year warranty and the repaired motor carries a 90-day guarantee.
T or f
False
belt tension will not have any affect on the wear of the bearings. True or false
False
Pulleys must be in proper alignment or belt and bearing wear will occur.
True or false
True
Open winding will not affect the resistance reading of the start winding as well as the resistance reading between the run and start terminals. True or false
False
If the resistance of the run winding is lowered, the imbalance in magnetic fields between the start and the run winding will be increased, and the starting torque of the motor will actually increase.
True or false
True
If a resilient mounted motor develops a short to frame, that technition can simply cut the ground strap wire as a permanent repair. True or false
False
Before testing a run or start capacitor with an ohmmeter, the capacitor should be discharged with a 20,000-ohm 5-watt resistor.
True or false
True
The electrical components for a fully welded hermetic compressor are checked at the disconnect box for the compressor unit.
True or False
Fales
Unit 36
The total heat content of infiltrated air of the same dry-bulb temperature may vary from one part of the country to another because of difference in _____.
humidity
A homeowner plans to build a house out in Las Vegas, Nevada, in the middle of the desert. It would be in his/her best interest to lower the “solar load,” to locate most of the windows on the _____.
North and south
The solar load on a structure is the heat gain resulting from the _____.
Heat from the radiation of the sun
More than one evaporator coil circuit is used when _____.
there will be an excessive pressure drop by using a coil circuit.
The most popular material combination used in air conditioning evaporators and condensers is _____.
copper and aluminum
In the reciprocating and scroll type motor-compressor assemblies, the motor is cooled by _____.
air over the shell of the assembly & suction gas return to compressor
In rotary type motor-compressor assemblies, the motor is cooled by _____.
discharge gas from the compressor
A dirty condenser coil can lead to _____.
Reduce the efficiency
High efficiency condensers _____.
have more surface area than standard
when exposed to the Salt air,___ should be used for the screws to secure the sheet metal of cabinets of air conditioning equipment.
Stainless steal
On a package air conditioning system, which refrigerant lines must be field installed?
None
the package air conditioning system is ___ then the split system because it’s completely Factory assembled and charged with refrigerant
is it more efficient or less efficient?
More efficiant
appearance is a major drawback with that type of air conditioning equipment
ductless split system
the moisture content of the air in different locations of the country must be taken into account When selecting air conditioning
True
Tru
The air temperature of the air off an evaporative cooler is _____.
Is cooler than
After being threaded many times, the screw holes in condenser cabinets may become oversized; if so, replace the screws with new ones of the same size.
T or F
False
If a structure has no attic, there should be sufficient insulation in the roof to minimize the heat gain in the occupied space
Truee or false
True
Air-conditioning equipment will perform at its best efficiency when running at full load.
T or f
Tr
If a residential split air-conditioning system has a compressor equipped with a start capacitor and relay, it is probably using a thermostatic expansion valve as a metering device.
T or f
True
the supply duct portion of an air handling system needs to be insulated when run through an unconditioned space
T
One drawback using custom-made, pre-measured duct section is that _____.
They have to be precise or the job will not fit and and be costly
What two fasteners are used with fiberglass duct?
staples and taps
What fastener is commonly used with round flexible duct?
self-tapping screws and Draw bands
_____ used at the end of a metal duct run will help reduce any noise that may be traveling through the duct.
Flexible duct
A boot in a duct system is used _____.
between the branch duct and register
A trap in the condensate line prevents _____.
A. Air from being drawn up into unit the end of the drain
b. foreign from being being pulled into the condenser
C. the pump turning on if the float fails
D. Both a and B
D. Both a and B
A good way to fasten insulation to the inside of sheet metal duct is to use_____.
tabs and adhesives
What two fasteners are used with fiberglass duct?
staples and tape
An auxiliary drain pan under an air handler is required when the air handler is installed_____.
above a traffic area
After refrigerant lines have been installed, they should be evacuated to a _____ vacuum.
deep
One purpose of a flexible duct connector in a duct system is to reduce the transmission of noise and vibration.
True or False
True
Application of acoustical lining to the interior of the duct is accomplished by using tabs, glue, or both
True or False
True
Power to the control transformer is controlled by the conditioned area thermostat.
True or False
False
When hanging a horizontal air handler, it should be pitched toward the drain port for proper condensate removal.
True or False
False
the sun shinning on the panels and coils of the condensing unit section will lower the efficiency of the unit
True or False
true
When installing a split air-conditioning system with a remote condensing unit, the line set may be altered if the standard length was incorrect for installation.
True or False
true
When removing the rubber plugs from a line set, the hiss indicates that the tubing is not leaking.
True or False
True
When the length of quick-connect precharged line sets is altered, the charge will not normally have to be altered.
True or False
False
Once the power has been connected to the condensing unit of a package air conditioner, it is a good idea to start the compressor immediately to make certain it runs.
True or False
False
A fitting used to change the size of a square or rectangular duct is called transition
True or False
True
Unit 40 Most occupants will normally operate their systems at about\_\_\_\_\_ degrees F. A. 68 B. 72 C. 75 D. 80
c. 75
AHRI rates condensers with\_\_\_\_\_ degrees F air passing over them. A. 72 B. 75 C. 85 D. 90
D. 90
At what conditions are AC systems rated? A. 95 F outdoors - 70 F DB - 50% indoors B. 95 F outdoors - 75 F DB - 50% indoors C. 95 F outdoors - 80 F DB - 50% indoors D. 100 F outdoors - 80 F DB - 60% indoors
C. 95 F outdoors-80 F DB - 50% indoors
At typical operating conditions, the standard AC system will operate with an evaporator boiling point of \_\_\_\_\_ F. A. 40 B. 45 C. 50 D. 55
A. 40
A normal evaporator superheat at the evaporator outlet in a standard efficiency AC system operating under design conditions will be\_\_\_\_\_ F. A. 10 B. 15 C. 20 D. 25
A. 10
At typical operating conditions, the high efficiency AC system will operate with an evaporator boiling point of \_\_\_\_\_ F. A. 40 B. 45 C. 50 D. 55
B. 45
A more accurate rating system for AC equipment that takes into consideration operation during the complete cycle is the \_\_\_\_\_ standard. A. ARI B. ACCA C. SEER D. EER
C. SEER
Ratings that are not completely accurate are known as \_\_\_\_\_ A. load ratings B. maximal ratings C. nominal ratings D. floor ratings
C. nominal ratings
Since the evaporator absorbs both sensible and latent heat, humidity must be taken into account and considered part of the load on the evaporator.
True or False
True
High efficiency condensers can actually be too efficient on cool days.
True or False
True
The larger the EER rating, the less efficient the equipment.
True or False
False
Typically, the fan will run on high speed when the outdoor temperature is above 100 degrees F.
True or False
false
its 85
The evaporator_____heat.
absorb
The condenser_____heat.
reject
A 4 ton AC system that requires an output power of 5kW would have an energy efficiency ratio of 16.5
True or False
False
its 9.6
The electrical operating conditions are measured with a volt-ohmmeter and a(n millivolt meter
True or False
False
its with ammeter
For residential AC units,230V single-phase is the typical voltage.
True or False
True
A 4 pole motor runs at 800 rpm.
True or False
false
its 1800 rpm
Air-conditioning systems normally move 800 cfm of air per ton
True or False
False
its 400
As a rule of thumb, the air leaving the evaporator will be about_____than the air entering the evaporator.
C. 17-20 degrees cooler
A service valve can be used to ____.
B. isolate the refrigerant so the system can be serviced
A typical evaporator superheat reading at the evaporator outlet for a central AC system on a 95 F day would be_____F
C. 10-12
On a 95 F day, the R-22 refrigerant pressure on the high side should be about_____psig.
243
The liquid line temperature is used to determine the _____ of a condenser
subcooling
To accurately add refrigerant to a system, a condenser ambient temperature of_____ F should be simulated.
95
The instrument to use to check for a short in the compressor motor winding is a(n)_____.
Ohmmeter
True or False
With a rise in outdoor temperature, the head pressure will rise.
True
True or False
Superheat occurs in the condenser as well as the evaporator.
False
True or False
The best way to tell if a compressor’s discharge line is at the correct temperature is to grab hold of it.
False
True or False
Subcooling occurs in the evaporator as well as the condenser.
False
True or False
When checking the electrical circuits of an AC system, each parallel circuit should be isolated and checked separately.
True
True or False
If a compressor has a partially shorted winding, it could run for a while, overheat, and shut off.
True
On most gauge manifolds, the suction or low side gauge is located on the Left
True
Temperature difference is used to describe the difference in the inlet and inlet temperature of a heat exchanger.
True or False
False
its the outlet temperature
Two types of fix-bore metering devices are capillary tubed and Orifice
True or False
True
Reducing the CFM through the evaporator will cause the amperage draw of the compressor to decrease
True or False
true
What two fasteners are used with sheet metal square and rectangle duct
“S” fasteners (slips) and drive clips.
