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CFESA Chapter 17 Defrost

Terms in this set (15)

What are the advantages of using low pressure control on a cooler?
Be sure an off cycle defrost by having the cut in pressure set above the pressure corresponding to 36 degrees
What restrictions are there to using low pressure controls?
They cant be used as controls for temp in low ambient temps with some refrigerants. they cant be used on cap tube systems
Two ways that a thermostat can be installed in a cooler?
In air stream or in evap coil
Which way is best and why?
In the coil and this type of installation can better ensure defrost on the off cycle
Where should the thermostat sensor be mounted if mounted in evap coil?
2/3 of the way down the evap coil tubing in the fins
When do coolers have more problems trying to keep frost off the evap coil?
When relative humidity levels are high and the doors are opened frequently
When is forced defrost needed on a cooler and how is it done?
When trying to mainttain box temp at the low cooler temps like 34-35 degrees. Install a time in the circuit to shut down the condensing unit for about 30 minutes a couple times a day
How to set commercial defrost timer?
In most timers there are pins to set the defrost times and an adjustable spring loaded pointer to set the length of the defrost cycle. Other timers may be pins to set the start and. stop times for defrost
Two basic types of defrost timers used in commercial refrigeration?
Time iniated/terminated and time iniated/temp terminated
In a commercial freezer, what are the three areas that must be considered in defrost cycle?
The evap coil, the evap drain pain and evap drain line
What is a defrost termination/fan delay thermostat and how does it work?
Thermostatic control that actuates a solenoid in the timer to take the timer out of defrost when coil reaches a certain temp and keeps the evap fans from coming on until the coil reaches about 20 degrees
What kind of defrost timer is required with a defrost termination t stat?
DEfrost timer with mechanical release solenoid or special relay to terminate defrost
Why is a defrost system with defrost termination t stat so much more efficient
Keeps freezer in defrost only as long as needed to clear evap coil of ice and frost
What causes ice build up on the ends of the evap coil where the return bends and expansion valve is located?
ICe builds up in this area because the lines are so much colder than the dewpoint of the air in the box. KEeping the covers on these areas will help reduce the buildup
When should defrost cycles be set to occur?
When doors are being opened most frequently. 12am, 6am, 12 pm, 6pm
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