CFESA Chapter 17 Defrost
What are the advantages of using low pressure control on a cooler? - answer 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? - answer 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? - answerIn air stream or in
evap coil
Which way is best and why? - answerIn 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? - answer2/3
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? -
answerWhen relative humidity levels are high and the doors are opened frequently
When is forced defrost needed on a cooler and how is it done? - answerWhen 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? - answerIn 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? - answerTime
iniated/terminated and time iniated/temp terminated
In a commercial freezer, what are the three areas that must be considered in defrost
cycle? - answerThe evap coil, the evap drain pain and evap drain line
What is a defrost termination/fan delay thermostat and how does it work? -
answerThermostatic 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? - answerDEfrost
timer with mechanical release solenoid or special relay to terminate defrost
What are the advantages of using low pressure control on a cooler? - answer 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? - answer 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? - answerIn air stream or in
evap coil
Which way is best and why? - answerIn 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? - answer2/3
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? -
answerWhen relative humidity levels are high and the doors are opened frequently
When is forced defrost needed on a cooler and how is it done? - answerWhen 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? - answerIn 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? - answerTime
iniated/terminated and time iniated/temp terminated
In a commercial freezer, what are the three areas that must be considered in defrost
cycle? - answerThe evap coil, the evap drain pain and evap drain line
What is a defrost termination/fan delay thermostat and how does it work? -
answerThermostatic 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? - answerDEfrost
timer with mechanical release solenoid or special relay to terminate defrost
