2-20
Defrosting operation
(1) Defrosting system
A hot-gas defrost system is adopted in the units; i.e. the high temperature and high pressure refrigerant
(hot gas) from the compressor is sent to the evaporator and drain pan for defrosting. Since the evaporator
is heated directly by the hot gas (refrigerant), defrosting can be performed effectively.
(2) Defrosting initiation
Defrosting is initiated by the timer or the manual defrost key.
However, defrosting is not initiated when frosting on the evaporator can not be detected.
¡
Evaporator inlet temperature : 5˚C or higher
¡
Evaporator outlet temperature : 20˚C or higher
q
Initiation by timer (Timer is set at the electronic controller, refer to section 3.3.2 for its operating method.)
Type of timer
Defrosting interval set
Function
Long timer
3, 6, 9, 12, 24 and 99
※
1
hours are
Regardless of the control temperature, defrosting
selectable.
is initiated according to the selected interval.
Defrosting is initiated every 4 hours until the control
Short timer
4 hours
※
2
temperature comes within the in-range after pull-down.
When the temperature is in-range, defrosting timer
will change into the selected long timer.
After the control temperature comes within
Out-range timer
30 minutes
in-range once, defrosting will be started 30 minutes later if
the control temperature rises out of the in-range.
※
1. Refer to "(3) On-demand defrost"
※
2. 6 hours when the control temperature is –20˚C or below.
w
Starting by MANUAL DEFROST key (on the operation panel sheet key)
Press the MANUAL DEFROST key, then press the ENTER/ESC key while indicate "ON" on the LED
display. The manual defrosting operation starts.
e
Initiation by frost detection
If the suction air temperature does not drop at the speed of 0.2˚C/1hr during frozen pull-down
operation, defrosting will be initiated because it is judged that frost is formed on the evaporator.
However, if the suction temperature is –20˚C or lower, defrosting will not be initiated. (activated)
(3) On demand defrost
When "99" in long timer is selected, defrosting is activated upon the condition of frost on evaporator
coil. This function is only for Frozen setting (SP < –10.1 deg C). and starting with 12 hours.
(If this function is selected for chilled setting, defrost initiates every 6 hours automatically.)
Procedure:
Step 1: After defrost, the controller records compressor running time for 1
st
1 hour. (T1)
Step 2: When 12 hours passed after defrost, controller records compressor running time for last 1
hour (T2). And the controller check whether the below condition is satisfied.
Step 3: If the above condition is satisfied, defrost is activated.
If above condition is not satisfied, defrost is postponed another one hour.
After counting up 13 hours, then repeat "Step 2".
Defrost will be postponed every one hour until the above condition (Step 2) is satisfied.
(Max. 24 hours)
T2 > T1
×
1.15
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