Installation Bulletin
P D - G 4
Page 9
Sequence Of Operation
Starting Sequence
Move control switch "S1" to the “On” posi-
tion. This will provide power for SSM1-SSM4
(solid state motor protectors), through flow
switch T1 (low water temp. safety), cycling
thermostat T2 Stage 1, through LL1 (lead-lag
switch), to energize R1 (non-recycle relay) and
TD1 (stage start relay). Contacts
1
and 3 of R1
close providing power through HP1 (high
pressure safety), LPF1 (low pressure freeze
safety), SSM1 and SSM2, OP1 (oil pressure
safety). contacts 4 and 6 of R1, to energize
SOL1 (liquid line solenoid).
When SOL1 opens, low side pressure Increases
to the cut-in setting of LP1 flow pressure con-
trol). LP1 closes, energizing compressor con
tactor Cl, which provides power to compressor
motor No. 1.
TD1 times out, closes contacts 2 and 4 of TD1.
If T2 Stage 2 is calling for cooling, power is
provided through LL1, contacts 2 and 4 of TDI
to energize R3 and TD2. Contacts 1 and 3 of
R3 close providing power through OP2 to
energize C3 which provides power to com-
pressor Motor No. 2.
Compressor motors No. 3 and No. 4 (ref. cir-
cuit No. 21, start in same sequence as No. 1
and No. 2 through T2 Stage 3 and 4, TD2 and
TD3 TD4 stages starting between compressor
motors No. 3 and No. 2 when LL1 is in op-
posite position.
The fan circuit is interlocked through auxiliary
contacts CIA, C3A. C5A, C7A of contactors
Cl, C3, C5, C7 respectively. to energize fan
contactor C9 when the high side pressure in
creases to the cut-in setting of FCP1 or FCP2
(fan cycling pressure control). Fan Motor M2
and M3 are energized through their respective
ambient thermostats FCT1 and FCT2.
P u m p - D o w n S e q u e n c e
T2 Stage 4 is satisfied and opens, R4 de-
energizes, contacts
1
and 3 of R4 opens de-
energizing C7. Compressor Motor No 4 drops
off the line.
T2 Stage 3 is satisfied and opens, R2 de-
energizes, Contacts
1
and 3 and 4 and 6 of R2
open, SOL1 de-energizes and closes. Contactor
C5 remains energized through auxiliary contact
C5B until the low side pressure drops to the
cut-out setting of LP2. When LP2 opens, C5
de-energizes and compressor Motor No.3 drops
off the line.
Circuit No.
1
de-energizes in the same se-
quence as circuit No. 2 through T2 Stages 2
and 1. in response to return water temperature.
Optional Accessory Sequence
Part Winding Start (208/230 Volt Units Only)
A time delay relay is wired in series with
compressor contractor C2 and delays
energizing of C2 for 1 second after Cl is
energized.
Unloading solenoid(s) mounted on com-
pressor head is energized in response to
return water temperature, by cycling
thermostat T2.
Non-Short Cycling
Non-short cycling relay (TD5) is energiz-
ed through N. C. contacts of R7 at
start-up and immediately following
pump-down. TD5 times out closing con-
tacts 3 and 4 of TD5. This allows R1 to
become energized on cooling demand
anytime unit has been off for 5 minutes.