Rotary Compressor
This compressor is small and light weight and uses blades or vanes to move the refrigerant.
Screw Compressor
This compressor is used on large chilled water systems 20 tons and up. It uses the spacing between the lobes of the screws to compress the refrigerant and will operate smoothly even when its capacity is reduced to as low as 10%.
Scroll Compressor
This compressor is the newest type of compressor and has no intake or discharge valves except a check valve on the discharge. It has very little wear and tear because it has so few moving parts.
Centrifugal Compressor
This compressor is used in large commercial refrigeration systems over 50 tons. It uses impellers or wheels and has no valves or pistons and operates at high speeds.
systems
This compressor is a piston type compressor used in domestic and commercial
False
The compressor is a liquid pump
a. Use color coded wires
b. Plug holes to prevent wall drafts from affecting the thermostat
c. Maintain tight wire connections
(d. All of the above Correct)
When installing a low voltage thermostat you should
True
Digital thermostats usually display temperature, time of day, programming and operating status.
12,000
How many btu's make up one ton of refrigeration
When using a single transformer system
When using a low voltage T-stat for heating and cooling, when would there be a jumper between Rh and Rc?
Low voltage
What is the most common type of T-sat in the HVAC industry?
False
Most thermostats in the HVAC industry are 120 volts.
a. 24 volts
b. 208 volts
c. 120 volts Incorrect
(d. any of the above)
Contactor coils are
False
Heat is not a form of energy
Metering Device
In a refrigeration system, which device is responsible for regulating the flow of refrigerant into the evaporator setting up a pressure difference between the high inlet pressure refrigerant and the low pressure refrigerant in the evaporator.
Fan Center
What device is added to a oil or gas forced hot air system when it is not AC read
Fahrenheit & Celsius
Name the 2 Temperature Scales
have some type of head pressure control
An air-cooled condenser that is operating in a climate that has four distinct seasons must ____.
The refrigeration effect equal to the melting of one ton of ice in 24 hours
What is a ton of refrigeration?
True
Air cooled condensers consist of an enclosure containing one of more fans.
15�F
If an R-12 refrigeration system has its air-cooled condensing unit on a 100�F roof and the condenser outlet temperature (refrigerant) is 115�F, with how much subcooling is the condenser operating?
The correct answer is: Desuperheat, Condense & Subcool
What are the functions of the condenser?
insulator
Mineral deposits in the water portion of a water-cooled condenser act as ____.
on the suction line between the evaporator and the compressor
The TXV sensing bulb is mounted ____.
increases the flow of refrigerant
When the load on the evaporator increases, the TX valve ____.
False
As the load on an evaporator increases, the automatic expansion valve will open to allow more refrigerant to enter the evaporator.
a. cycling the condenser fan
b. controlling dampers in the airstream through the condenser
c. flooding the condenser with refrigerant
(d. all of the above Correct)
Control of the head pressure in an air-cooled condenser is done by ____.
True
Shell and coil condensers are available in horizontal and vertical designs. Select one:
1/4 to 200 ton
Single water cooled condensers have a capacity ranging from ____________________.
True
Shell and coil condensers are more compact than a shell and tube condenser.
b. The superheat in the evaporator would decrease.
c. Liquid refrigerant would flow back to the compressor.
(d. All of the above are correct. Correct)
If a thermostatic expansion valve's thermal bulb came loose from the suction line at the outlet of the evaporator, which of the following could result?
a. The bulb pressure would increase and the thermostatic expansion valve would open.
True
The step-motor valve uses a small motor to control the valve's port, which in turn controls evaporator superheat.
all of the above
The condenser in a refrigeration system ____.
superheat
A TXV is designed to maintain a proper
False
An AX valve works best when the evaporator load is constant.
True
A capillary tube controls the refrigerant flow into the evaporator.
a. produce a reduction in the pressure on the liquid refrigerant
b. regulate the flow of refrigerant into the evaporator
c. lower the boiling point of the refrigerant far enough below the temperature of the load to get the needed heat transfer rate
(d. al
The primary function of an expansion device is to ____.
The purpose of a capillary tube is to ____.
a. regulate the refrigerant flow into the evaporator
b. lower the pressure of the liquid refrigerant
c. lower the boiling point of the refrigerant
(d. all of the above)
When recovering refrigerant, it is important not to mix different refrigerants in the same container because; the mixture may be impossible to reclaim
False
An automatic expansion valve uses a thermal bulb to help control the amount of refrigerant being fed into the evaporator.
At the outlet of the metering device
Where does flashgas occur?
evaporator suction line superheat
A thermostatic expansion valve controls refrigerant flow to the evaporator based on ____.
goggles with side shields and gloves
When transferring refrigerants from a cylinder to a refrigeration system or any other container, you should always wear ____.
True
Refrigeration is the process of removing heat from a space.
a. sight glass
Name one system accessory used in a refrigeration system?
True Correct
Keep torches away from combustible materials.
False
Seeing bubbles in a sight glass means the system is low on charge.
polyol esters
Alkyl Benzene and________________ are synthetic oils.
frostbite
Liquid refrigerant can cause __________________.
False
Refrigerant needs to be recharged often because it gets used up in a system.
Ashrae
_______________________ addresses refrigerant toxicity and flammability.
-14 Degrees F
R134 a at 0 psig will boil at _________.
False
A high pressure control can be used to control the condenser fan to maintain the proper operating pressures.
a. thermostat, safety
What two controls can a low pressure control be used as?
False
Flash gas occurs in the compressor during the off cycle.
a. refrigerant
_____________ provide cooling for compressors
False
The high side pressure gauge reads the pressure from the compressor to the condenser.
low ambient control
An example of an operating control may be a ___________.
False
Excessive head pressure will cause the compressor to sweat.
c. metering device, compressor
The low pressure gauge reads the pressure from the _________ to the ________________.
a. left side
b. blue gauge
c. compound w gauge Incorrect
(d. none of the above)
What is another name for the low side gauge?
jump out the pressure control
What is step three of pumping down your gauges?
d. crankcase heater Correct.
A_________________ can reduce and stop refrigerant migration.
c. to the compressor
Where does the domestic bimetal overload mount?
b. large commercial refrigeration Correct
A centrifugal compressor is used in _________________ systems.
True
The dome of a rotary compressor is on the high side of the system.
b. at the shaft seal Correct
Where do leaks occur on an open drive compressor?
False
Net oil pressure will vary, normally between 30 and 40 psia.
False
Scroll compressors use valves to pump refrigerant.
a. compression Incorrect
b. evaporation
(d. both a and b)
A condenser removes heat via heat of _______________.
False
A compressor can pump liquid.
True
A screw compressor can be hermetically sealed.
False
The dome of a reciprocating compressor is on the high side of a refrigeration system.
d. last few passes
Subcooling takes place in the __________________ of the condenser.
True
Reciprocating compressors are used in domestic and commercial refrigertion systems.
Boil
A dirty condenser can cause the oil in the compressor to _______.
b. chilled water
A screw compressor is used for ___________________ and refrigeration systems.
a. water jacket
If a semi-hermetic compressor is wate cooled it uses a ______________ around the compressor.
d. water boxes
Another name for a shell and tube condenser is _________________.
True
A semi-hermetic compressor is welded together.
c. solid state controlled
A_________________ expansion valve uses a thermistor as a sensing element.
superheat , pressure
The capillary tube does not control
valve body, diaphragm,needle and seat,adjustment and packing gland,the sensing bulb, transmission.
List the components of a TXV:
c. It opens to allow more refrigerant into the coil
How does a TXV respond to a load increase?
True
Both the TXV and the AXV need a place to store the refrigerant when it is not needed. This storage tank is called a receiver.
2020
What year will R-22 production be totally banned?
d. none of the above
What are the three temperature ranges for Commercial refrigeration?
d. prerssure drop
How does a capillary tube control refrigerant flow?
c. 2 psig
An external equalizer is required for a commercial refrigeration application when the pressure drop exceeds__________________.
valve, fixed-bore
The metering device can either be a _____________ or a _____________.
c. hot gas from the discharge line from the compressor
What is used to accomplish hot gas defrost?
c. recover the refrigerant
What is the first step to field repairing a leaking heat exchanger?
d. Float type Correct
What does a flooded evaporator normally use as a metering device?
True
Dehumidifying the air means to remove the moisture and this is frequently desirable in refrigeration systems.
False
The three pressures that actually open,close and modulate the expansion valve are the bulb, evaporator and core.
8 to 12 degrees
What would be considered as the normal system superheat?
False
Refrigerant entering the evaporator is a 60% liquid and a 40% vapor mixture.
reverse
The AXV responds differently than the TXV to load changes. It actually acts in
it is the process of removing heat from a place where it is not wanted and transferring it to a place where it makes little or no difference.
Explain Refrigeration.
steel, brass, copper, stainless steel or aluminum
Evaporators may be manufactured from
c. particular refrigerant , group of refrigerants Correct
Each TXV is designed for a _______________ or ______________.
c. 15 minutes
After making an adjustment on a TXV how long should you allow the system to operate before making additional adjustments to the TXV?
It is the difference in the temperature between the boiling refrigerant temperature and the evaporator outlet temperature
Describe evaporator superheat.
Stamped and finned tubed evaporators
What are the two types of evaporators used in the HVACR industry?
True
One advantage to a rotary compressor is it can pull a deeper vacuum.
True
Liquid slugging usually causes immediate damage.
False
A high pressure control can be used to ocontrol the condenser fan to maintain the proper operating pressures.
True
In order to maintain a proper superheat reading you need to allow the system to run at least 15 minutes.
a. thermostat, safety
What two controls can a low pressure control be used as?
c. ASHRAE 34-1992
_________________________ addresses refrigerant toxicity and flammability.
False
The high side pressure gauge reads the pressure from the compressor to the condense
aev
A ________ is an example of a metering device.
a. evaporator
A dirty _________________ will cause the suction Pressure to drop.
False
An automatic expansion valve uses a sensing bulb as one of its operating pressures.
True
Bare coil evaporators are used in older systems.
none of the above
What is another name for the low side gauge?
a. electric heater
What does this symbol means �^^^^^^� ?
d. 2020 Correctpage 482
What year will R-22 production be totally banned?
d. fans Correct
Fin and tube evaporators use _____ to help with cooling a refrigerator.
False
A dry type evaporator uses more refrigerant than a flooded type evaporator.
d. prerssure drop
How does a capillary tube control refrigerant flow?
False
Plate type evaporators are used in commercial systems.
c. boil
A dirty condenser can cause the oil in the compressor to _______.
8 to 12 degrees
What is the normal superheat for a TXV system?
False
A semi-hermetic compressor is welded together.
True
The metering device controls the flow of refrigerant to the evaporator coil.
c. 75%
The start relay will remove the start circuit when the compressor reaches ______ of the full rpm's.
False
You can use a hammer or knife to remove ice from a shelf type evaporator.
a. natural convection
Two principal types of evaporator are called_____________________ and forced convections.
b. high
If you have a starving coil your superheat will be _______.
b. low
If you have a flooded coil your superheat will be ________.
b. the refrigerant directly cools the air
What is meant by direct expansion evaporator operating designs?
a. external equalizer
An ____________________ is used if there is a pressure drop greater than 2.5psi in the evaporator.
c. increase
A clockwise turn of the TXV stem will______________ the superheat.
c. solder
How is a capillary tube attached to the suction line?
True
Another name for a distributor is an octopus.
b. chilled water
A screw compressor is used for ___________________ and refrigeration systems.
True
Flooded type of evaporators are almost full of liquid.
c. It opens to allow more refrigerant into the coil
How does a TXV respond to a load increase?
False
A capillary tube can be adjusted to maintain a constant pressure.