Test 5 Flashcards
Solenoid Valve
An electro-magnet opens and closes
the valve
– Used to stop and start refrigerant flow
Magnetic coil energized (powered)
–
Plunger rises
– Refrigerant pressure lifts seat
– Fluid flows through valve
Magnetic coil de-energized (no power)
–
Plunger falls
– Refrigerant pressure closes seat
– No fluid flow through valve
Solenoid for Pumpdown
•(suction line)
Refrigerant in the suction line during off-cycle
can cause problems
Refrigerant may migrate to the compressor oil
So Compressor will be damaged on startup
•
A pumpdown removes refrigerant
before the
compressor shuts off
Improper Installation
• Flow direction is marked on the valve
– Look for an arrow, or the word “IN”
• If installed backward,
– Refrigerant will leak through
Solenoid valves control refrigerant flow
•
By
– “Automatic” or “Continuous” pumpdown
• The unit pumps down
until LP control stops compressor
Hot Gas Bypass
Solenoid valves are used in hot gas
bypass to:
– Raise the evaporator temperature, or
– Defrost the coil in freezers
Head Pressure Regulating (HPR) Valves
keeps what up in low amibient?
If refrigerant backs up what is this called and where does it happen?
head pressure
“flooding” the condenser
•
HPR Acts like
an overcharge of refrigerant
–
Compressor has to raise head pressure
Aka
Also known as “hold-back” valves
What does Evaporator Pressure Regulator (EPR) Valve do in evaporator?
– Keeps evaporator pressure and
temperature up
EPR also maintains stable…
Where would this be located…
• product temperature
• Located in the suction line
Does EPR sense evaporator pressure?
Does it rise or open on inlet pressure?
Yes
Rise
–
Sporlan calls EPR
an ORI valve
Evaporator #1:
– Walk-in refrigerator (25°Evaporator)
• Evaporator #2:
– Candy case (34°Evaporator)
• Where do you install the EPR?
– Near the highest temperature evaporator
What does a Crankcase Pressure Regulator (CPR) Valve look like?
Does CPR close or rise on of outlet pressure?
Hint: the C in CPR
• Looks like an EPR, but…
– Closes on Rise of Outlet pressure
What does CPR stand for?
What is it sometimes also called?
Crankcase Pressure Regulator
Closes on Rise of Outlet pressure- CRO
•
–
Does CRO ALSO sense crankcase pressure?
Where would this be located?
Yes
Located in the suction line near compressoe
CPR Keeps crankcase pressure down to prevent what?
Prevents compressor overload during hot pull down
(after freezer defrost)
Freezer Hot Pull Down
• Compressor shuts off during defrost
• Defrost heaters warm freezer evaporator
Evaporator pressure and temperature rises
So what happens next?
And what can overload compressor?
So After defrost, the compressor starts
– High evap pressure
Adjust CPR valve when
It is warm
Water Regulating Valves
•
Used on water-cooled condensers
• Maintains head pressure
–
Water regulatting valves also
Regulates water flow to condenser
