Defrost Operation Control; Defrost Cycle Type; Starting The Defrost Operation - Mitsubishi Electric CMB-WP1016V-GA1 Service Handbook

[ VI Control ]

Defrost Operation Control

-7- Defrost Operation Control

(1) Defrost cycle type

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.
HBC refrigerant system
Low-pressure
pipe
T16
High-pressure S
pipe
Refrigerant flow

(2) Starting the defrost operation

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.
Outside temperature
(TH7)
Cumulative compressor
operation time
Pipe temperature
(TH6)
1) Outdoor unit pipe temperature (TH6)
SW3-3 OFF
SW3-3 ON
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.
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.
HWE1410A
21S4Mb
T14
Cooling-main
heat exchanger
Water
Water
T12
T15
LEV2
LEV3
M
HIC SV1
PS
PS3
Condition 1
-5ºC [23ºF] or above
90 minutes or more if the defrost prohibit timer is set to 90.
The pipe temperature has
stayed below the temperatures
in the table below (Note1) for
three minutes.
-8ºC
-5ºC
21S4Ma
T13
Heating-main
heat exchanger
Water
Water
PS
PS1
T11
LEV1
Condition 2
50 minutes or more
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.
- 74 -
HBC water system
Water pump WP2
T34
T33
T32
Refrigerant Refrigerant Refrigerant
Refrigerant
Water pump WP1
Water pressure
protection valves
Water purge
Expansion Water
valve
supply
tank
Condition 3
-5ºC [23ºF] or below
250 minutes or more
The pipe temperature has
stayed below the temperatures
in the table below (Note1) for
three minutes
Strainer
S
Air purge valves
Strainer
T35
S
GB