Controlling The Plate Heat Exchanger 2; Defrost Operation Control - Mitsubishi Electric PUHY-RP200 Service Handbook

[ VII Control ]
-9- Controlling the plate heat exchanger 2 (Solenoid valve (SV3))(Opens when ON)
ŒThe valve positions in different modes are summarized in the table below.
Mode
Cooling
Refrigerant oil recovery in the cooling
mode with the compressor operated
at low frequency
Heating
Defrost
Refrigerant oil recovery in the heat-
ing mode with the compressor oper-
ated at low frequency
When high pressure (63HS1) rises in
the heating mode

-10- Defrost Operation Control

(1) Starting the defrost operation
ŒThe defrost cycle will start when all of the three conditions (outside temperature, cumulative compressor operation time, and
pipe temperature) under <Condition 1>, <Condition 2>, or <Condition 3> are met.
Outside temper-
ature (TH7)
Cumulative
compressor op-
eration time
The pipe temperature has stayed at or be-
low -10ºC for three minutes or the 63LS
reading has stayed below the value ob-
Pipe tempera-
tained from the formula "1.5 + 0.02 x TH7"
ture (TH3)
ŒIf 10 minutes have passed since compressor startup or since the completion of a defrost cycle, a forced defrost cycle can be
started by setting DIP SW2-7 to ON.
ŒEven if the defrost-prohibit timer is set to 90 minutes (or 250 minutes for "Condition 3" to be met), the actual defrost-prohibit
time for the next defrost cycle is 50 minutes if the last defrost cycle took 12 minutes.
ŒAll units in the heating mode will simultaneously go into the defrost cycle in a system with multiple units. Units that are not in
operation will remain stopped.
(2) Defrost operation
Outdoor unit
HWE10010
SV3 turns on if high pressure (63HS1) exceeds 2.98 MPa while the compressor is
operated at the minimum frequency.
Condition 1
-5ºC [23ºF] or above
50 minutes or more
90 minutes or more if the defrost prohibit timer is set to 90.
for three minutes.
Compressor fre-
quency
Outdoor unit fan
SV1a,SV1b
SV3
21S4a
LEV1
LEV2
SLEV
SV3
OFF
OFF
OFF
OFF
ON
Condition 2
-5ºC [23ºF] or below
The pipe temperature has stayed below the
value obtained from the formula "Outside
temperature (TH7) -5ºC" for three minutes,
or the 63LS reading has stayed below the
value obtained from the formula "1.5 + 0.02
x TH7" for three minutes.
Model
RP200 model
RP250 model
RP300 model
RP350 model
Stopped
ON
OFF
OFF
480 pulses
1400 pulses
480 pulses
- 98 -
Condition 3
250 minutes or
more
The pipe tem-
perature has
stayed at or
below -10ºC
for three min-
utes.
Compressor frequency
60Hz
60Hz
65Hz
65Hz
GB