Final Study Guide Hvac Maisy Flashcards
if a resilient mounted motor develops a short to the frame the tech can simply cut the ground strap wire as a permanent repair
false
before testing a run or star capacitor with an ohmmeter the capacitor should be discharged with a 20,000 ohm a fully 5 watt resistor
true
the electrical components for a fully welded hermetic compressor are checked at the disconnect box for the compressor unit
false
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
On a package air conditioning system, which refrigerant lines must be field installed?
Condensing line, power & low voltage line
The solar load on a structure is the heat gain resulting from the _____.
radiation of the sun
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
More than one evaporator coil circuit is used when _____.
there will be an excessive pressure drop in the coil circuit.
A popular material combination used in air conditioning evaporators and condensers is _____.
Copper tube and aluminum fin
Fractionation occurs when
some of a blended refrigerant evaporates or condenses before the rest of the blend
Using a restrictor, liquid refrigerant can be charged into the low-side of the system with the system operating.
true
When charging a refrigeration system with a near-azeotropic mixture, what must be done to prevent liquid from entering the system?
Charge as a liquid through the low side using a restrictor.
Refrigerant in vapor form is normally put into the system through the
suction line
When charging a system with vapor refrigerant from a refrigerant cylinder, the cylinder will become
cold
A manufacturer’s charging chart may be used when available to determine the correct charge for a system.
true
Wear all your equipment including
Glasses
Hat
Boots
Gloves
The factory charge in a split system, using R-22, shows 6 lb. 8 oz. in the outdoor condensing unit and 2 oz. in the evaporator. The 3/8” liquid line contains 0.48 oz. per foot and the 7/8” suction line contains 0.10 oz. per foot. The refrigerant lines are 30’ long. What is the correct refrigerant charge for this system?
7 lb 11 oz.
When adding refrigerant in liquid form into the high-side of the system, the system motor/compressor assembly is running.
false
One good feature of an electronic charging scale is that it counts upward as refrigerant is removed, to tell the technician how much refrigerant was used.
true
Charging a refrigeration system refers to
adding refrigerant to a system
When charging liquid refrigerant from a single valve supply cylinder, the cylinder is placed
upside down
Refrigerant in liquid form is normally put into the system through the
liquid line
When your in customer home, you must give consideration to what issue?
Tarps
When adding refrigerant in vapor form to an operating refrigeration system, the refrigerant must be added to the low-pressure side of the system.
true
If 22 oz. of refrigerant are to be added to a refrigeration system and the supply cylinder weighs 24 lb. 12 oz. before any is added, what will be the supply cylinder weight after the system has been charged?
23 lb 6 oz.
If a critically charged refrigeration system is over charged, which of the following is a likely result?
Increased operating pressures.
If the tank is a reusable tank, there are no check valves and system refrigerant can enter the tank as long as the system pressure is higher than the pressure in the tank.
true
The quickest method to charge a system is to charge only vapor.
false
Air-conditioning equipment will perform at its best efficiency when running at full load.
true
High-efficiency condensers
have more surface area than standard condensers
In rotary compressors, the motor is cooled by
discharge gas from the compressor
The air temperature of the air off an evaporative cooler is
cooler than the entering air
The moisture content of the air in different locations of the country must be taken into account when selecting air-conditioning equipment.
true
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.
True
In reciprocating compressors used in air conditioning, the motor is mainly cooled by
Air over the shell of the assembly
Suction gas returning to the compresser
A dirty condenser coil can lead to
reduced efficiency
If 30 oz. of refrigerant are to be added to a refrigeration system and the supply cylinder weighs 26 lb. 4 oz. before any is added, what will the supply cylinder weigh after the system has been charged?
24 lb 6 oz.
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.
false
If a structure has no attic, there should be sufficient insulation in the roof to minimize the heat gain in the occupied space.
True
The supply duct portion of an air handling system need to be insulated when run through an unconditioned space.
True
One drawback of using custom made, pre-measured duct sections is that ____.
a. if the measuring was not done correctly, the job may not go together
b. the sharp edges provide possible safety issues
c. altering a duct section at the job site is extremely cost-ineffective
What two fasteners are used with fiberglass ductboard?
staples and taps
A fitting used to change the size of a square or rectangular duct is called a _______.
Transition
What fastener is commonly used with round flexible duct?
Draw bands or self-tapping screws
A good way to fasten insulation to the inside of sheet metal duct is to use _____.
Tabs or adhesives(glue)
An auxiliary drain pan under the unit is recommended when the evaporator is installed _____.
above the conditioned space.
_____ 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 the register
A trap in the condensate line prevents _____.
A. air and foreign material from being drawn up into the drain line
B. additional cooling load from warm air being drawn up into the air handler
After refrigerant lines have been installed, they should be evacuated to a _____ vacuum.
deep
Most occupants will normally operate their systems at about_____ degrees F.
75
AHRI rates condensers with_____ degrees F air passing over them.
95
At what conditions are AC systems rated?
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.
40
A normal evaporator superheat at the evaporator outlet in a standard efficiency AC system operating under design conditions will be_____ F.
10
At typical operating conditions, the high efficiency AC system will operate with an evaporator boiling point of _____ F.
45
A more accurate rating system for AC equipment that takes into consideration operation during the complete cycle is the _____ standard.
SEER
The_____rating is a steady-state rating and does not account for the time the unit operates before reaching peak efficiency.
EER
Ratings that are not completely accurate are known as _____
Nominal ratings
As a rule of thumb, the air leaving the evaporator will be about_____than the air entering the evaporator.
17-20 degrees cooler
A service valve can be used to ____.
a. check the electrical service to the compressor
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
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
One purpose of a flexible duct connector in a duct system is to reduce the transmission of noise and vibration.
TRUE
Power to the control transformer is controlled by the conditioned area thermostat.
false
When hanging a horizontal air handler, it should be pitched toward the drain port for proper condensate removal.
false
The sun shining on the outdoor section of the AC system has a direct affect on the operation of the unit.
True
When installing a split AC system with a remote condensing unit, the line set may be altered if the standard length was incorrect for installation.
True
When removing rubber plugs from a line set, the hiss indicates that the tubing is not leaking before installation.
true
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
High efficiency condensers can actually be too efficient on cool days.
true
With a rise in outdoor temperature, the head pressure will rise.
true
Superheat occurs in the condenser as well as the evaporator.
false
The best way to tell if a compressor’s discharge line is at the correct temperature is to grab hold of it.
false
Subcooling occurs in the evaporator as well as the condenser.
false
When checking the electrical circuits of an AC system, each parallel circuit should be isolated and checked separately.
true
If a compressor has a partially shorted winding, it could run for a while, overheat, and shut off.
True
When the length of quick-connect precharged line sets is altered, the charge will not normally have to be altered.
false
Application of acoustical lining to the interior of a duct is accomplished by using tabs, glue, or both.
true
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.
false
The magnetic fields generated in the rotor and stator of a motor causes the rotor to be pushed around the shaft.
false
The heavier the load on an operating motor, the greater the amount of slip.
true
In order to change the direction of rotation of a split-phase motor, the technician must change the direction of current flow through the start winding.
true
The centrifugal switch mounted on the shaft of a split-phase motor has a normally closed contact.
True
an open winding in an electric motor means that
a wire in a winding is broken
Which of the following voltages are not safe for a 208-V motor to operate?
170 volt and 238 volt
If the voltage supplied to the motor is well below the motor rated voltage, the current draw will be _____ it should be.
higher than
The voltage tolerance of a standard electric motor is ___.
+10% -10%
The locked-rotor amperage is normally ___ times as great as the run-load amperage.
5
A direct-drive motor is usually connected to a load with a ___.
coupling
Which of the following statements are correct when referring to large refrigerant or nitrogen tanks?
a. The protective cap must be on
b. Safety Goggles or glasses must be worn when moving
c. Large Tanks should not be carried, but moved with an approved cart
