Carel pCO Manual page 19

Compressors shift
Selecting the compressors shift ensures longer life to the compressors. This procedure, in fact,
makes them work in a very balanced way and compensates the number of their on/off routines as
well as their working hours.
The shift is based on a F.I.F.O. logic: the first compressor that turns On will be the first to turn Off.
At the very beginning this logic might cause an unbalanced compressors management but the
system will gradually settle.
Upon a call for compressor ON, the logic will be as follows:
- the compressor that has been Off for the longest time-interval will be the first to start;
- the first compressor that turns On will be the first to turn Off;
- any compressor will turn On again only after all the other compressors have turned On.
Compressors timer
pCO also controls the working hours of the compressors. Set the required value (default 10,000
hours) in the dedicated mask. When the compressors reach the set threshold an alarm message
prompting maintenance will be displayed.
Fans
Fans are managed on the basis of a 'steps control action'. After having selected set-point and
differential, a series of steps will automatically be created within the working zone. The number of
steps depends on the number of fans. The dedicated masks will show the On routines of each single
fan. The steps relative to the unused fans will be calculated beyond the working zone, so the fans
will never be activated. Fans will start according to the values measured by the high pressure
transducer (delivery side of the compressors). Fans shift is also available.
Inverter
The analogue output Y1 (0 - 10 Volt) is used to control an inverter; in this way the fans will be
managed according to the values measured by the high pressure probe. The purpose of this function
is to keep the condensation pressure as close as possible to the set-point by modulating the speed of
the fans. As a result, the fans will work less and with less noise, especially when the external
temperature is low.
Ver. 1.0 dated 21/10/94 19