Parallel Switchback
If the EPC fails to maintain control of the
rack, its Switchback Relay de-energ i z e s
allowing the normally closed contacts to com-
plete the Time Delay Switchback Relay cir-
cuit. After a 24 second delay, the Switchback
Relay opens the circuits to:
T3 on all the rack’s compressor boards
and closes the circuits to
T4 on half the boards, plus Time Delay Split
Relay.
After another 24 second delay, the Split Relay
closes the circuits to:
T4 on the remaining half of the boards.
With a compound rack the medium tempera-
ture side is brought on first, and the low tem-
perature side by the Split Relay.
HUSSMANN CORPORATION • BRIDGETON, MO 63044-2483 • Printed in USA
ELECTRICAL Revised August 1, 1996
4 - 14
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