Hussmann RDI-27 Installation & Operation Manual page 36

Refrigeration control with two compressors
This group of applications can be used if the controller is to cut
two compressors in and out.
The functions can be compared with wiring diagrams 1 to 3, but
instead of controlling fans the relay is here used for compressor
2.
The two compressors must be of the same size. When the
controller demands refrigeration it will rst cut in the compres-
sor with the shortest operating time. After the time delay the
second compressor will be cut in.
When the temperature has dropped to "the middle of the dif-
ferential", the compressor with the longest operation time will be
cut out.
If the running compressor does not manage to reduce the tem-
perature to the cutout point, the other compressor will be cut in
again. This happens when the temperature reaches the top part
of the di erential. If the temperature is instead "stuck" in the dif-
ferential for two hours, there will be a change-over between the
two compressors so that the operating time can be equalised.
The two compressors must be of a type that can start up against
a high pressure.
The compressors's settings for "Min On time" and "Min O time"
will always have top priority during normal regulation. But if one
of the override functions is activated, the "Min On time" will be
disregarded.
If the controller is to cut 2 compressor and 1 fan in and out, relay
4 must cut the fan in and out.
This function is activated in application 10.
Simple refrigeration with defrost
This application can be used where there is only regulation of
refrigeration and defrost.
Heating function
This application is the same as under 1, but a heating function
has been added which protects the unit against too low tem-
perature. The defrost function's heating element is here used for
heating.
This application is used where the temperature can go below
the set cutout temperature for the refrigeration. To ensure that
the temperature will not become too low the heating element is
activated x degrees below the reference value.
The S3 sensor must be mounted. It supplies the signal when
there is heating.
AK-CC 210 Manual RS8EP502 © Danfoss
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