Table 16: Trip lock
Par. nr.
Name
Set value
Default value
14-20
Reset Mode
Automatic reset x10
Automatic reset x10
14-21
Automatic reset time
30s
30s
Stop compressor in case of safeties (LP, HP, DGT)
Table 17: Stop compressor in case of safeties (LP, HP, DGT)
Safeties
Tripping conditions
Re-start conditions
Value
Time
Value
Time
HP safety switch
See Pressure setting and max
DGT in Operating envelope da-
ta
Immediate, no delay. No by-
pass
Conditions back to normal
Switch closed again
Manual reset
LP safety switch
Manual or Automatic Maximum
5 auto reset during a period of
12 hours, then manual reset.
DGT external
4 Way valve control and defrost logic
The main challenge of a system equipped with a 4-way valve is during the time of the switch period. After that
switch, condenser becomes evaporator and vice versa. Pressurized liquid in condenser directly
flows
to the
compressor suction and lead to oil dilution and in extreme case, liquid slugging.
Liquid
flood
back due to reversing cycle can be reduced by using pressure to transfer liquid refrigerant from one
exchanger to the other before the 4-way valve switch. Following
flow
chart describes the strongly suggested
sequence by Danfoss.
Time and pressure
difference
have to be
fine-tuned
during system
qualification.
EXV Opening degree and time have
to be set to keep a minimum pressure
difference
to allow 4-way valve switch.
In any case, defrost logics must respect requirements and tests described in Manage Superheat and Operating
envelope data sections. Maximum speed 100rps is proposed for defrost cycle.
Start defrost
Stop Compressor
Set EXV @40% (manual mode)
Stop Compressor
Set EXV @40% (manual mode)
Switch 4 way valve
Set EXV automatic mode
Switch 4 way valve
Set EXV automatic mode
Start Compressor @max.100 rps
Start Compressor
Differential pressure
<3 bar or >2 minutes
Differential pressure
<3 bar or >2 minutes
Defrost
completed AND
>3 minutes
End defrost
CC-000213
Unit remotely controlled
If the system demand, and thus compressor speed, can be controlled remotely, for example by a building
management system (BMS), it is essential to make sure the demand signal is consistent. Unit controller shall not
directly transmit demand from external signal to compressor. Table below show some examples of erratic external
demand signal and possible preventions.
Scroll compressors, VCH115 | Frequency converter
© Danfoss | Climate Solutions | 2023.08
AB392939083370en-000202 | 30
