Refrigeration Final Exam
What is the temp on walk in Freezers
-10 degrees
How much system efficiency is gained by every 1 degree of subcooling
.5%
What is the temp on a reach in Freezer
0 degrees
What should the slope of the suction line be
1/8 per foot of 1/16 per foot direction of refrigerant flow
What is normal Subcooling for refrigeration
10 degrees
What is normal superheat on a refrigerator
10 degrees
The water leaving a water cooled condenser is 100 degrees what does the indicate the condensing temp should be?
110 degrees (water cooled about 10 degrees)
The air entering a walk in Freezer air cooled condenser is 90 degrees, what should the condensing temp be
115 degrees (freezer CS 25)
The air entering a walk in refrigerator air cooled condenser is 90 degrees, what should the condensing temp be?
120 degrees (refrigerator CS 30)
Which of the following start capacitors will replace one rated at 145 - 147uF x 240 VAC
145-174uF x 440VAC
What is normal Subcooling on high seer(efficiency)
15-20 degrees
What is the usual range of minimum and maximum water pressure for most ice machines
20 PSIG to 80 PSIG
What is the normal evap TD for a walk in refrigerator or Freezer
20 degrees (35 box - 25 evap = 10)
What is the normal evaporator TD for a Reach in refrigerator or freezer
20 degrees. (40 box - 20 evap =20)
What is the CS for Freezers
20 to 25 degrees CS
If a reach in is running at 42 degrees box temp, what should the evap temp be?
22 degrees (20 TD)
What size evaporator should you use with a 24,000 BTUH freezer condensing unit
24,000 BTUH
If a refrigerator box has a temp of 35 what would you expect the evaporator temp to be
25 degrees (based on a 10 degree TD)
If you need a 30 amp compressor contactor what can you use
30 amp inductive - 20 amp resistive
A walk in is running at 45 degrees box temp, what should the evaporator temp be?
35 degrees (10 TD)
What is the normal box temp on a medium temp walk in refrigerator
35 to 37 degrees
What is the temp for reach ins
38 to 40 degrees
What is the recommended slope on a freezer drain
4" per foot
What is the proper case temp for produce (veggies etc)
40 degrees
Based on TROT what is the approximate BTUH of a 5 HP medium temp compressor
40,000 BTUH
What is a units 24 hour ice production if it makes ice in 19 minutes drops ice in 1 and weight of each base is 6lbs
432 (1440/20)x6
How much do mechanical sub coolers cool the liquid
45 degrees
When troubleshooting a potential relay
5 and 2 are the coil, 1 and 2 are the relay contacts
The proper wiring sequence for a potential relay is
5 common, 2 start 1 Run
What is normal superheat on a freezer
5 degrees
If the ambient temp is 90 degrees what would you expect the Liquid line temp to be?
60 degrees (based on a 30 degree CS)
Store humidity above _________ will adversely affect open refrigerated case operations
60%
What is the approx leaving water temp of a water cooled ice machine
95 to 105 degrees
What do restaurants use to clean and sanitize their counters and equipment
A mixture of bleach and water ( 1 teaspoon bleach to a bucket of water
How often is it practical to replace the oil in a vacuum pump?
After every 5 evacuations or after each evacuation of highly contaminated systems
Why is it important to stock product with product load lines marked in the case
Air flow will be disrupted causing air flow to be directed outside the case
What info is needed to compare ice machines current production to the manufacturer chart for that machine
Ambient and water temp, slab weight and total production time
Which of th following will most likely cause a door gasket to deteriorate
Animal fat from hands of food handlers
What is the diff between commercially frozen meat and home frozen meat
Commercial freezing is done faster
The contact arrangements on potential and current relays currents relays are?
Current NO and Potential relay NC
What can cause high condensing temps
Dirty condenser, overcharge of refrigerant, non-condensate in the system
What controls the case temp in most supermarket cases on parallel rack systems
EPR valve
What is the best thing to do before evacuating a refrigeration system?
Evacuate the gauge and pump connections to ensure all connections are tight
An external overload is tripping Does not tripping, but does not trip when the terminal box cover is removed you should?
Find out why the overload is tripping
What does a superheat of 5 degrees or below indicate
Flooding
What would a superheat of 0 degrees always indicate
Flooding back to the compressor
What is the minimum requirement for a frozen product according to the FDA food code
Frozen hard
What is the best way to learn how to service an ice machine
Go to a factory sponsored seminar and training session
How does dirty or iced evaporator affect evap temps, pressure
Heat won't be absorbed so less temp, less pressure
How does an evaporator Load affect Evap Temps and pressures
High loads mean too much heat to absorb, both temp and pressure are high
If a TEV system is overcharged to a 40 degree condenser split the symptoms will be?
Higher head pressure and higher subcooling
How does a dirty condenser affect condensing temps, pressures
Higher pressure and temps (prevents rejection of heat)
What are 3 installation related troubleshooting problems a tech must check
Ice machine location, drainage and water supply
What is the Pure Ice that commercial cube ice makers produce
Ice that freezes without air, chlorine, or minerals in it
Run and start capacitors are wired
In series with the start winding
What does a high evaporator load do to Superheat
It would be high
How can refrigeration companies prevent customers from health department violations
Keep their customers equipment in good condition with a service contract
What will damage a 3 phase motor
Loss of phase or a voltage imbalance over 2%
What combination of symptoms ONLY occur on a unit with inefficient compressors?
Low head pressure and high suction pressure.
What cycle the compressor on most parallel rack systems
Low pressure controls
When any refrigerant system is low on refrigerant it will usually have?
Low suction and low head pressure
Why would a low ambient give a lower CS
Lower load more efficient
How does ambient temp affect the condensing temp and pressures
Lower pressure and temp
What is the quick method of calculating equivalent feet of run to determine pipe size
Measure the total run and multiply by 1.5
What is the CS for refrigerators
Most are 30 degrees CS at 95 ambient
Can the restaurant fool the inspector by making the thermometer to read lower temps than actual box tems
No the inspectors use their own thermometer
When replacing a compressor in a self contained reach in from R12 to R401 should you change the mineral oil to Alkylbenzene?
No, an oil change is not necessary when retrofitting close coupled systems
On a water cooled ice machine how much should be drained through the condenser during defrost
None
Why does a walk in fridge evaporator freeze up from too much load or open door.
Not enough off cycle to defrost the coil
What is the manufacture warranty coverage of most new ice machines
Only replacement of defective warranty parts during the warranty period.
Where is the P-trap of a walk in freezer supposed to be located
Outside the box
What does 20 degrees of above of Subcooling usually indicate
Overcharged
Micron gauge is not working properly, what is the first thing to do to correct it?
Pour alcohol into the inlet port to clean oil out of it.
What are the two most important factors for efficient supermarket equipment operation?
Proper installation and and an effective maintenance program
The incoming voltage to a contactor is 240 and the voltage leaving is 235 what should you do to fix it.
Replace the contact or contactor
What precautions should be taken when charging liquid through the suction service valve
Restrict the flow of liquid if the amperage is above 10% of RLA or the valve frosts
What can cause High superheat in a TEV metered evaporator?
Restrictions before the Receiver, liquid line dryer or metering device.
Why are starting components needed on a 1 phase motor
Single phase motors need a phase shift in order to start the rotor turning
What does a superheat of 20 degrees or above indicate
Starving
What is the most critical for proper walk in intallation
That the floor panels are level before the wall and door panels are attached
Which of the following statements in the most accurate when describing the replacement of an OEM relay with an electronic relay
The OEM relay is a more accurate relay than the electronic relay
What is condenser split
The difference between the Ambient temp and the Condensers temp.
What happens if warm product is placed in a refrigerator
The evap coil may freeze up which will reduce the fridges efficiency
What is the relationship of Evap TD to box humidity
The low the Evap TD the Higher the humidity
What is a Storage only walk in
The product entering the walk in is close to the walk ins designed temp
A 1 phase compressor (CSIR) has proper voltage, starts and runs for about 5 seconds, then goes out on overload, what is the problem.
The start relay contacts are welded closed
How do fixed metering devices react to what is going on in condensers or evaporator,
They are designed to feed a fixed amount so they don't really change.
How does a TEV act to what is going on in the condensers and evaporator?
They try to maintain a constant superheat in the evaporator so can feed more or less.
Why do supermarkets use split condensers on their parallel rack systems
To keep head pressure up in cold ambients
Why is the compressor started in the 2nd part of a triple evacuation?
To release moisture that may be trapped in the oil.
What does a 5 degrees or below of Subcooling usually indicate
Undercharged
What are the some considerations when charging refrigerant into a system high side?
Unit capacity is over 5 lbs in a vacuum, and compressor is off.
How do you get the Evaporator Temp?
Use the suction pressure and convert Pressure to Temp on a P/T chart
What is heat reclaim
Using discharge vapor to heat the store or its domestic water
How is evaporator temperature or TD calculated
Using the difference between the evaporator temp and the temp of the box.
What does a superheat of 10 degrees indicate
Usually properly charged.
How do you charge an R134a refrigerator with a cap tube system
Weigh in the charge per the nameplate
What is a common cause of clear algae and slime in an ice machine
Yeast from production of fresh bread and also from beer
Will an ambient of 70 degree give a lower CS than 95 degree ambient?
Yes
If the FDA code only requires a 41 degree food temp but local code requires 40 can the county inspector cite for 41 degrees
Yes the FDA is a minimum and local codes can be stronger
