7. Defrosting
control
(reverse
defrosting
method)
• Frost formation temperature
is 29.3 °F (-1.5°C).
• If the outdoor units are a
combination of different
models, defrosting
operation, once started,
cannot be manually
terminated for about 2
minutes.
• To protect the refrigerating
cycle circuit, the fan mode
may be controlled during
defrosting.
• During defrosting control,
compressors are controlled
so that their speeds do not
exceed 76.6 rps.
1. Defrosting commencement c
onditions
•
During heating
ope
ration, the
cumulative
durat
ion
of operation
in
which TE1 and
TE2 sensor temperature falls below frost formation temperature is measured, and
when this reaches 55 minutes, defrosting control is introduced. (Just after startup
or upon changeover from cooling to heating, the target cumulative duration is 25
minutes.)
* If the outdoor units are a combination of different models, all the units begin engaging
in defrosting control as soon as one of them satisfies defrosting commencement
conditions.
2. Details of defrosting control
1)All compressors currently in operation are operated at the minimum speed.
2)When a specified amount of time passes from the time the compressors reached
the minimum speed, the outdoor fans are turned off by closing the 4-way valves.
And the PMV4 opening operated at the target opening for defrosting control.
3)All compressors currently not in operation are turned on and operated at the target
rotational speed for defrosting control.
3. Defrosting termination conditions
• Defrosting termination conditions are met when the TE1 and TE2 temperature
sensor measurement reaches a specified value (roughly 53 °F (12°C)) a certain
period of time after the commencement of defrosting control. In that event,
defrosting termination control takes over.
* If the outdoor units are a combination of different models, defrosting termination
control commences when all the units satisfy the defrosting termination conditions.
As long as one or more outdoor units are yet to satisfy the defrosting termination
conditions, those that have engage in standby operation.
4. Details of defrosting termination control
1)Compressors are operated at the standby operation speed.
2)When a specified amount of time passes, the 4-way valves are opened.
3)Indoor heating refrigerant recovery control is performed.
For control details, see “ 7. Refrigerant/oil recovery control”.
• During standby operation,
compressor speed is in the
24-33.5 rps range.
(It varies from outdoor unit to
outdoor unit.)
Item Description of operation, numerical data, and other information Remarks
− 60 −
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