Lab Flashcards
What is compressor flooding?
What damage does it cause?
How to prevent it?
Small amounts of liquid refrigerant in compressor.
Air cooled compressors - wears pistons and causes blow-by
Suction cooled compressors- dilutes oil & decreases lubrication
Prevent: Ensure 20 F Superheat
What is compressor slugging?
What damage does it cause?
Large amounts of liquid refrigerant entering compressor.
Broken internal parts.
What is a flooded start in a compressor?
How do you prevent flooded starts?
Flooded starts is refrigerant migration in the off cycle to the compressor.
Prevented by crankcase heaters and pumpdown/pump out control modes
What temperature does oil lose it’s lubrication?
300 F
What temperature does oil begin to break down?
350 F
How far from the discharge port do you measure overheating temperature and what is the maximum allowed temperature at this point?
6 Inches from discharge port and no more then 225 F
Current Relays have a NO or NC set of contacts?
NO
Potential Relays have a NO or NC set of contacts?
NC
Current relays are often used on what type of compressor?
Hermetic Compressors
Potential Relays are normally used on what type of compressors?
Semi-hermetic Compressors
Potential Relays are in series or parallel with the start winding?
Parallel
Current relays are wired in series or parallel with the run winding?
Series
Start capacitors must not exceed what % of their rated mfd?
130%
What type of contacts does a PTC relay have?
No set of contacts
Hot Wire Relays have how many sets of contacts?
2
Run Capacitors stay in the circuit, true or false?
True
Adding micro farad ratings in a parallel circuit is done by?
MFDt=MFD1 + MFD2
Potential Relays Contacts switch on an increase or decrease of voltage?
Increase
Adding micro farad ratings in a series circuit is done by
1/MFDt = 1/MFD1 + 1/MFD2
What happens to current relays contacts when the compressor hits LRA?
The contacts close
Relief valves are sized and rated according to?
SCFM or lbs of dry air per minute
According to Ashrae the relief valve settings must be…?
25% higher than the maximum expected operating pressure and not higher than the pressure rating of the vessel
Run capacitors can be replaced with what % larger than it’s original size?
110%
Start Capacitors help with what?
Starting Torque
Start Capacitors stay in the circuit. True or False?
False
RSIR has what type of capacitor?
No Capacitor
RSIR keeps the start winding in the circuit. True or False?
False
RSIR motors are only found alongside fixed orfices and cap tubes?
True
CSIR has what kind of capacitor?
Start Capacitor
CSIR motors can be used with TXV’s. True or False?
True
CSCR has what kind of relay?
Potential Relay
In a CSCR motor the caps are in series or parallel?
Parallel
PSC stands for what?
Permanent Split Capacitor
The start winding does what in a PSC motor?
Stays in the circuit
PSC motors have what type of capacitor?
Run Capacitor
Line Duty overloads directly or indirectly cut power to the compressor?
Directly
Pilot Duty overloads cut power to the compressor how?
Indirectly via contactor or relay
Inherent overloads combine which two properties?
Heat and current
The write pin connects which two parts of a reciprocating compressor?
Piston and the connecting rod
In a Defrost Timeclock, Defrost termination occurs between which two sets of contacts?
3 and X
In a Defrost Timeclock, the normally open contacts are between which numbered conatcs?
1 and 3
In a Defrost Timeclock, which two contacts are always jumpered?
1 and 2
Oil Failure controls are automatic resets. True or False?
False
OFC use what device to utilize either 120 or 208 supply voltage?
Drop Resistor
If the capillary lines off of an oil failure control are inadvertently reversed in connections the result would be?
The compressor will start and then go off on oil failure
Where is the ideal bulb postion on the suction line for pipe 7/8” & larger?
4 or 8 o’clock
Where should you NOT mount the TXV bulb?
6 o’clock
What is the purpose of all evaporator feed devices?
Reduce the pressure and meter refrigerant into the evaporator
What is the opening force of a TXV?
Bulb Pressure
What is the closing force of a TXV?
Evaporator Pressure & Spring Pressure
An oversized TXV will do what to the evaporator?
Hunt
An undersized TXV will do what to the evaporator?
Starve
You must use an externally equalized TXV with what piping device?
Distributor
You must use an externally equalized TXV if the pressure decrease the evaporator is greater than what?
2 F
TXV is rated in what?
Tonnage
The bulb of a externally equalized TXV should be mounted upstream or downstream of the equalization port?
Downstream
Cap Tube minimum and maximum length?
6 inches minimum & 18 Inches maximum
Capillary Tubes are critically charged systems. True or False?
True
Bubble point is directly related to what?
Subcooling
High side floats are critically charged? True or flase?
True
The first symptom of an overcharge of a system using a high side float would be?
Flood back to the compressor
High side floats maintain what?
A constant liquid level in the high side of the system
The first symptom of an overcharge in a system using a low side float would be?
High Discharge Pressure
An AEV’s opening force?
Spring Pressure
An AEV’s Closing force
Evaporator Pressure
An undercharged high side float will do what to the evaporator?
Starve it
What accessory will prevent overfeeding in low loads and underfeeding in high loads?
Accumulator
What does nominal mean?
Normal conditions
What is the range of a “c” bulb charge?
50 to -10 F
What is the range of a “z” bulb charge?
0 to -40 F
What is the range of a “x” bulb charge?
-40 to -100 F
A gas charged bulb has a Maximum Operating Pressure. True or False?
True
The best liquid line filter drier for removing moisture is?
Molecular Seive
A service valve must be in which position to put your gauges on?
Back seat
Oil separators remove oil in the what and return it to where?
Discharge line and return it to the crankcase
Where is the best place for a sight glass?
Downstream of the liquid line filter drier
Solenoid valves are gravity sensitive. True or Flase?
True
A solenoid valve will do what if installed backwards?
Will not close
Suction line accumulators hold what percentage of total charge?
50%
Which liquid line filter drier is best for removing acids?
Activated Alumina
What is the job of an EPR Valve?
To prevent suction pressure from getting too low
What is an EPR’s operating action?
Open on Rise of Inlet
What is the closing force of an EPR valve?
Spring Pressure
What is the operating action of a CPR valve
Closes on Rise of Outlet
What is the job of a CPR Valve?
Prevents the compressor from overamping by limiting the suction pressure the compressor see’s
What is the opening force on a CPR valve
Spring Pressure
An LAC Valve must be used in conjuction with what other device?
A check valve
What is the operating action of a headmaster control valve?
Open on Rise of Outlet
A Hot Gas Bypass Valve is used for what?
Capacity Control
What additional device is needed if the HGBV is equipped to the outlet of the evaporator?
Desuperheating TXV
Increased air velocities in an evaporator will increase or decrease the RH
Decrease the RH
A draw through fan should be 2/3 in or out of the shroud?
2/3 in the shroud
A blow through fan should be 2/3 in or out of the shroud?
2/3 out of the shroud
A 4 way reversing valve used in a heat pump system in Canada with the reversing valve solenoid energized you must be in?
Cooling Mode
A defrost differential regulator valve’s purpose is to…?
Lower the liquid pressure below the discharge pressure when a system is in defrost mode
A large temperature difference will cause low RH and can dry out exposed product, True or False?
True
What two characteristics of refrigerant help with oil return?
Refrigerant velocity and Refrigerant miscibility
What are two application for a 3 way solenoid valve?
Heat Reclaim and Hot Gas Defrost
