Parallel Switchback
If the EPC fails to maintain control of the rack, its
Switchback Relay de-energizes allowing the nor-
mally closed contacts to complete the Time Delay
Switchback Relay circuit. 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 temperature
side is brought on first, and the low temperature
side by the Split Relay.
ELECTRICAL
September 1, 1997
4 - 14
HUSSM ANN CORPORATION • BRIDGETON, M O 63044-2483 • Printed in USA
EPC Compressor
Controller Contacts
O
P
C# Aux Cont
C#
TD
NO
4
2
1
BL
BR
120
O
GY
GY
HP
Oil Failure
O
W
R
T2
T1
T3
T7
T4
T5
T6
T8
S1
T10
T9
P1, 1
P1, 2
P1, 3
P1, 4
P1, 6
P1, 7
P2, 3
P2, 5
K1
K2
Alarm LED
H Press LED
Run LED
Alm
G
Y
R
R
R
P
P1, 8
T
P1, 5
BL
BR
B
O
R
W
K2
K1
K1
K1
C# Protector
Motor Cont Coil
Fuse LED
Circuit
R
P2, 2
Y
F1
P2, 1
O
K1
Oil LED
Circuit
Power LED
LP
Figure 4-9 Parallel Switchback Controls
R
Y
BL
B
BL
X1C
X22
Time Delay Switchback (TDSB) Relay
EPC Switchback Relay
P
P
Y
Y
W
X1
TD
T4
T4
T4
T4
T4
X24 X2D
W
W
W
Compressor Board #1
on Compressor Board #2
on Compressor Board #3
on Compressor Board #4
on Compressor Board #5
on Compressor Board #6
BL
BL
BL
BL
BL
BL
BL
R
24 Sec Delay
24 Sec Delay
Time Delay Split (TDSP) Relay
TD
TDSB
24 Sec Delay
Figure 4-9 — Parallel Switchback Controls
Return to Contents
