Finals Review Flashcards
Superheat Calculation
Suction line temp - SST
Subcooling Calculation
SDT - Liquid Line Temp
Evaporator Superheat - Where to take temp?
Outlet of the evaporator
System Superheat - Where to take the temp?
4-6” from inlet of compressor
Condenser Subcooling - Where to take the temp?
Measured at the outlet of the condenser
System Subcooling - Where to take the temp?
Inlet of the TXV (Metering Device)
Evaporator T.D
SST - Return Air
Evaporator Delta T
Return Air - Supply Air
Condenser Temperature Rise
Air Entering Condenser - Air Leaving Condenser
Condenser Split
Entering Air - SDT
Compressor Vibration Absorbers are used
Semi-Hermetics
Receivers can’t be lower than __% full
10%
Components that can not be used on capillary tube systems
Receiver
Filter Drier: Activated Alumina
High Acid, moderate moisture (Compressor Burnout)
Filter Drier: Molecular Sieve
Low Acid, High Moisture
Filter Drier: Silica Gel
High Moisture
Acceptable temp drop across a Filter Drier
2 F
Direct Acting Solenoid Valve
Used in low flow/ pressure differential across valve
Pilot Operated Solenoid Valve
Uses system pressure to keep open & close
Most efficient type of Evaporator
Liquid Overfeed
Least Efficient type of Evaporator
DX Coil
On multi-evaporator systems, which would require an EPR valve
All but the coldest
When is a suction line solenoid valve used?
-To protect against undershoot
-Systems with long runs/evaps
-Re-Evaporator Systems
How to size a Accumulator
Capacity + Tonnage
What does a CPR protect against?
High load situations = High current draw due to High Suction Pressure
High Pressure safety cut out temperature?
130 F
Insulation Wall Thickness for different applications
HVAC/ Residential = 3/8”
Coolers = 1/2”
Freezers = 3/4”
Why use an unloader?
Keep Suction pressure up, T.D. up means less frost build-up
Suction-Cut off Unloader
cuts gas from entering the cylinder on the suction side
Hydraulic unloaders use what pressure to unload?
Oil Pressure
A de-energized oil port solenoid in a hydraulic unloader means the compressor is loaded or unloaded
unloaded
Purpose of a Lock-out Relay
Requires the triggering of a safety to be manually reset.
Lock-out Relays have 1 set of NO or NC contacts
NC
This defrost initiation requires a time clock and is most reliable
Time Initiated
this defrost initiation tracks compressor run time and is used in residential applications
Run Time initiated
This defrost initiation initiates when required and is MOST energy efficient
On-Demand
Defrost initiation that’s only used on off-cycle defrost applications
Pressure/ Temperature Initiated
Most common type of defrost termination
Temperature Terminated
4 Main types of defrosts
- Supplemental Heat Defrost
- Natural Defrost
- Frost Removal
- Manuel Shutdown
Recovery Time
The period right after refrigeration starts following a defrost.
Most common method of defosting in blast freezers/coolers
Hot Gas Defrost
On hot gas defrost the condenser fan motor is energized/de-energized?
de-energized: Tt keep head pressure up
Type of vapour defrost that runs out of heat quickly into the defrost cycle
3 pipe conventional flow
What is conventional flow mean
Refrigerant flows in the same direction during cooling and defrosting
Cons of 3 pipe conventional flow
- 3rd pipes expensive
- Damages pipe due to thermal shock
3 pipe conventional flow with re-evaporator has a SLSV. Is it open or closed during the main evaporators cooling cycle?
Energized to prevent excessive pressure drop
Reversing Cycle Defrost requires what other component?
Reversing Valve
Is the Reversing Cycle a conventional flow system
Nah mate
2 Pipe Reverse Flow requires what special valves
- Defrost Pressure Regulating Valve
- 3 way solenoid Valve
Defrost Pressure Regulating Valve is energized/de-energized during a defrost call?
De-Energized to create the pressure differential
On a Natural Defrost Off Cycle Pressure Operated, every time the LPC contacts open, the system is in a…
Defrost
most common combination of defrost initiation/termination for commercial freezer application?
Time in - Temp Out
When measuring a compressor discharge temperature. How much higher is it expected to be 6” away
50-75 F
A perfect storm of moisture, heat and acidity can cause…
Copper Plating
Higher discharge or Lower suction will more greatly affect the compression ratio?
Lower Suction
How will floodback on a suction cooled compressor present itself?
Damage to the crankshaft will get progressively less as per oil flow
Floodback on an air-cooled compressor will present itself as?
Damage at the cylinder
What condition will cause erratic damage inside the compressor
Flooded Start
Cap tues can not handle more than __% overcharge
10%
