VDH MC3-SC, Manual, Page: 23 / 45

MC3-SC Stepped Controller
Document no.: 140744 version 1.3
Page 23 of 45
P 21
Valve lifting can allow compressors to run with no load. This parameter lets you
adjust how long the valves may be lifted for.
P 22 A time can be set here stating how long the compressor must keep running as a
minimum before it can be switched off again.
P 23 If the suction-side pressure gets higher than this value, the first compressor will
switch on immediately. The minimum off time (P20) will however be observed.
P 24 If the section pressure drops below this value, the minimum on time will be ignored
and switching off can commence straight away.
P 25 If a frequency-controlled compressor is being used and a PI 0-10V output has been
chosen, then the corresponding P band is defined here. This is the distance to the
setpoint at which the compressor must be running at 100%.
In the case of a Bitzer continuous slide regulation, this is the second dead zone
within which the slide says in the same position. This band is symmetric around the
setpoint and is smaller than (i.e. lies inside) the P bandwidth of P12. When the
pressure rises above this bandwidth, more capacity will be provided, and if the
pressure drops out of this band, less capacity will be provided.
P 26 The I time associated with P25.
This parameter is not used for regulation with a Bitzer continuous slide.
P 27 If the maximum number of starts per hour is exceeded, the compressor will no
longer start until the starting time of the earliest startup was at least one hour ago.
P 28 & P 29 This is the time between two pulses when increasing or reducing the capacity of a
Bitzer continuous slide. The pulse duration is always 0.5s.
4.2 Condenser part
P 30 & P 31 The range that the discharge pressure setpoint can be set between from the front
P 32 The proportional band. This is symmetrical around the setpoint. As long as the
pressure is within this bandwidth, no fans will be enabled or disabled.
P 33 Minimum signal level from the analogue output. If the condenser fan has to run, it
will always run at this percentage (as a minimum).
P 34 Analogue amplification factor for the fan regulation, 1 to 100% where 100% means
full speed and 1% is the slowest regulated speed.
P 35 Step-up time between the fans. This time starts at the moment a fan is switched on.
Note! This is not a switch-on delay. For example, take a step-up time of 2 minutes.
Fan 1 comes online and the pressure remains steady. The timer now begins to run. If
the pressure now begins to rise after 2 minutes, fan 2 will come on straight away.
However, if the pressure begins to rise within the first 2 minutes, the timer will first
have to expire before the next fan can come online.
P 36 Step-down time between the fans. Works in the same way as P35.
P 37 The fans are stepped up and down in a fixed sequence.
4.3 Temperature sensors
P 40 & P 41 These parameters let you set whether or not any temperature sensors are connected
up and what the functions of those sensors are.