Commercial Refrig. Special Refrig. System Components Chapter 25

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Author:
salvatorefricano
ID:
296773
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Commercial Refrig. Special Refrig. System Components Chapter 25
Updated:
2015-02-25 22:21:18
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defrost pumpdown
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Description:
mechanical controls, electrical controls,defrost,pumpdown
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  1. Four Basic components of the system
    • Compressor
    • condenser
    • txv
    • evaporator
  2. Two- Temp controls
    EPR, Utilized when there are multiple evap in the system, that operate @ different temp.
  3. Evaporator pressure regulator does what
    • -Stops press. from leaving the evap.
    • -Prevents the pressure in an evap from dropping below a predetermined pressure.
    • -Modulates vapor.
    • -Adjustable for different pressure of individual coils
    • -Located on the suction line of each evap, except the lowest temp coil
  4. On multiple evap where would the check valve be installed.
    on the lowest temp coil
  5. Multiple Evaporator
  6. The Electronic Evaporator Pressure Regulator (EEPR) job is to do what, where is it located, used on what.
    • Accurate control
    • located at the evap outlet
    • used on single & multi evap
    • Multiprocessor senses & maintain air temp @ discharge
    • must be used in with a (CPR)

    uses a Bi-Polar motor.
  7. Crankcase Pressure Regulator does what.
    Where is it located.
    • Located close to the compressor
    • prevents compressor from overloading on start-up, and on hot pull downs
    • limits the press. entering the compressor
    • (CRO) Close on rise of pressure
    • ports sre located on different locations that the EEPR, but looks similar
  8. Adjusting the CPR
    • Shut off box and warm to 10* above thermostat C/I.
    • Put an amp-meter on the common wire of the compressor
    • Record the FLA from the nameplate
    • Turn on the system & watch the Amp draw
    • If the amp is not equal to the manufacturer amp, adjust the valve until it is equal
    • Record the suction line pressure in/out of (CPR)
  9. What is the location, purpose of a  Spring Loaded Relief Valve
    • It Releases refrigerant from a system when high pressure conditions exist
    • located in the vapor space
    • Resets after opening
    • Will Not release all the refrigerant into the atmosphere
    • Can be piped to a recovery tank in a fire proof room
    • Should never be by-passed, unless testing
  10. Where is the One time relief valve located, what are it's use's
    • Releases refrigerant from the system when a high pressure condition exist
    • fittings are filled with low-temp solder, melts @ 220*
    • Usually located @ the suction line near the compressor
    • It will release all the refrigerant at one time into the atmosphere.
    • Must take out of the system if you are brazing
  11. What are some causes of the Safety valve failing, other than fire
    • Condenser fan not working
    • Dirty condenser,causing high head pressure
    • Water pump not working
    • The biggest mistake you can make is,you will forget to check for a relief valve before servicing the system.
  12. What is the Sequence of the Automatic Pump Down start up
    • Box temp rises, thermostat close
    • Liquid line solenoid is energized
    • Refrigerant flows to the evaporator
    • the compressor is still off
    • When the low side pressure increases, the low side pressure control closes
    • The compressor is once again energized
  13. Automatic pump down system shutdown sequence
    • N/C liquid line solenoid valve controlled by a thermpostat
    • Thermostat opens whendesired box temp is reached
    • solenoid is de-energized  and close
    • compressor continues to pump
    • suction pressure drops
    • low pressure control opens when suction pressure drops
    • low pressure control, controls compressor operations
  14. Low pressure control applied as a thermostat
    • Control will cut off the compressor when the pressure equals the system pressure that corresponds to a temp of about 15* cooler than desired box temp
    • Control is rated by pressure and current draw of the contacts
  15. what are some low ambient controls, and when are they used
    • Motor master or Fan cycling switch: Controls fan speed
    • Dampers & louvers: Adjusts the volume of air at the tower
    • Fan cycling: cycles fan on or off
    • HPR: Floods condensor-regulates head press.
    • Balanced TXV: Floating head press, above & below 60*F, different seasons
    • They are used in areas when the ambient goes below 60*F
    • Tricks the system it's in design ambient(60-95)
  16. What does the Fan cycling head pressure control do, and
    • Causes large variances in head pressure
    • Device opens on drop in head pressure, turning condenser fan off
    • Device closes on rise in head pressure, turning condenser fan on.
    • Has a 40# diff between open & close
  17. How does a fan speed control for controlling pressure work
    • As outside temp drops, the fan slow down, reducing the airflow through the condenser
    • as the outside temp rises, the fan speeds up, increasing the airflow through the condenser
  18. What is the magnetic solenoid valve used for
    • Used to start or stop refrigerant flow
    • can be normally open or closed
    • must be installed in the direction of refrigerant flow
    • Often used in conjunction with automatic pump down
  19. What does the Low Pressure Switch do
    • Can be used as a low charge protection & space temp control
    • Prevents system from operating in a vacuum
    • C/O pressure set below normal operating pressure
  20. Setting the Low Pressure Control as a Thermostat on TXV systems ony
    • Box Temp converted to a pressure#= C/I
    • ___________________________________
    • Cut Out:
    • Pressure equal to 5* below box temp plus
    • pressure equal to evap TD, usually(20*), plus
    • pressure equal to 3* lower= C/O
    • Example: (R134a) 45* box temp, converted=40#-20*-5*-3*=17* convert=16#C/O
  21. How does the receiver ensure that only 100% liquid refrigerant enters the liquid line?

    Test?
    By means of dip tube.
  22. One use for a low pressure switch is?

    Test?
    For low charge protection.
  23. A condenser flooding system is sometimes used to provide low ambient temperature operation. To use this method, an extra device must be added to this system. The device is a___?

    Test?
    Over sized receiver.
  24. To protect the compressor during periods of a hot pull down a __ valve is used.
    • CPR (crank case pressure regulator)
  25. Refrigeration systems are designed to operate year round. For this reason they are equipped with___?
    • A low ambient control
    • Some type of head pressure control.
  26. Random defrost is accomplished how___?
    It occurs automatically during the off cycle of the compressor.
  27. When a system pumps down, where is the refrigerant stored?
    • Receiver
    • Evaporator
  28. Defrost using internal heat is accomplished using__?
    Hot gas from the compressor.
  29. What are some type of low ambient temperature head pressure control?
    • Pressure controlled dampers in the condenser air stream.
    • fan cycling
    • vfd, motormaster controls fan speed
  30. Two temperature operation of a refrigeration system is necessary when__?
    • More than one evaporator, each at a different temperature, is operating from one compressor.
  31. A hot pull down is when___?
    The load on the evaporator produces a suction pressure that increases the load on the compressor.
  32. As the adjusting spring on an evaporator pressure regulator is tightened, the pressure in the evaporator will____?
    Increase.
  33. The best way to adjust a CPR valve is by___?
    Adjusting the CPR to produce an amperage draw of the compressor motor to the motor name plate rating.
  34. A suction line accumulator is used to reduce the possibility of liquid refrigerant entering the compressor.

    True or False

    True
  35. An oil separator is installed at the suction intake of the compressor to ensure separation of the refrigerant and oil before entering the compressor. 

    True or False
    False
  36. The crankcase pressure regulator (CPR) puts a limit on the pressure that can return to the compressor
    true

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