Mitsubishi Electric City Multi CMB-WP108V-G, Service Manual, Page: 108 / 301

[
VII
Control ]
- 99 - HWE1113B GB
Defrost Operation Control
-5- Defrost Operation Control
(1) Defrost cycle type
Œ
The defrost cycle has following two types: Bypass defrost that is the same method as that used in a CITY MULTI series sys-
tem and heat recovery defrost (default) that the heat is collected from the water circuit and the defrost cycle ends early.
The following figure shows the refrigerant flow for the bypass defrost. In the bypass defrost method, LEV1 and 2 are closed
and the heat is not exchanged between the refrigerant and water. In the heat recovery defrost method, the defrost cycle ends
early because the heat is caught from the water.
The basic defrost method is the heat recovery defrost with the dip switch 3-10 on the HBC turned OFF (default). The bypass
defrost may be performed depending on the water temperature. Setting the dip switch 3-10 to ON performs the bypass defrost.
(2) Starting the defrost operation
Œ
The 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.
1) Pipe temperature(TH6)
Œ
If 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.
Œ
Even if the defrost-prohibit timer is set to 90 minutes (or 150 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.
Condition 1 Condition 2 Condition 3
Outside temperature
(TH7) -5ºC [23ºF] or above -5ºC [23ºF] or below
Cumulative compressor
operation time 50 minutes or more
90 minutes or more if the defrost prohibit timer is set to 90.
250 minutes or more
Pipe temperature
(TH6) The pipe temperature has
stayed below the temperatures
in the table below (Note1) for
three minutes. The pipe temperature (TH6)
has stayed at or below the val-
ue obtained from the formula
"Outside temperature (TH7) -
10ºC [18ºF]" for three minutes.
or the 63LS reading has stayed
below the value obtained from
the formula "1.5 + 0.02 x
(20+TH7)" for three minutes. The pipe temperature has
stayed below the temperatures
in the table below (Note1) for
three minutes
SW3-3 OFF -8ºC
SW3-3 ON -5ºC
Refrigerant flow
SVM1
HIC
TH15
TH16
LEV3
TH12
S
S
LEV1
TH13
PS1
TH11
TH14
Water Water Water Water
Cooling-main
heat exchanger
Heating-main
heat exchanger
21S4Ma
21S4Mb
HBC water system HBC refrigerant system
TH33
TH32
TH34 TH37
Water pump WP2
Refrigerant Refrigerant Refrigerant Refrigerant
Water pressure
protection valves
Water pressure
protection valves
Water pump WP1
TH36
TH35
S
S
LEV2
PS
High-pressure
pipe
Low-pressure
pipe
Water vent
valve Expansion
tank Water
supply