McQuay SEASONCON ALP-037A, Manual, Page: 40 / 43

OPTIONAL CONTROLS
SPEEDTROL - HEAD PRESSURE CONTROL
ALP-037A thru 078B
The SPEEDTROL system of head pressure control operates
in conjunction with FANTROL by modulating the motor
speed on tans 11 and 21 in response to condensing pressure.
By reducing the speed of the last fan as the condensing
pressure falls, the unit can operate at lower ambient
temperatures.
The SPEEDTROL fan motor is a single phase, 208/240
volt, thermally protected motor specially designed for
variable speed application. The solid state speed controls
SC1 1 and SC21 are mounted inside the compressor
compartment near the top of the condenser coils. Units
with 460 volt power have a transformer mounted on the
back of the control box to step the voltage down to 230
volts for the SPEEDTROL motor.
The SPEEDTROL control starts to modulate the motor
speed at approximately 230 PSIG and maintains a mini-
mum condensing pressure of 170 to 180 PSIG.
DAMPERTROL - HEAD PRESSURE CONTROL
ALP-089B thru 159B
DAMPERTROL is an optional system for reducing con-
denser capacity. It consists of an assembly of damper
blades, linkages and blade operators installed over the first
fan turned on by FANTROL (fan no. 11) and arranged to
operate as shown. The blade operators sense condenser
pressure and extend or contract in response to the pressure
to open or close the damper blades as required to maintain
adequate condenser pressure. The operators are factory set
to begin opening the damper blades at
5 PSIG and to
be fully open at 250 10 PSIG.
DAMPERTROL IN OPEN POSITION DAMPERTROL
IN CLOSED POSITION
DAMPER
S E C T I O N
C O I L
To check the damper blade operator pressure settings,
the unit should be started with the fuses removed from fans
11 and 13 (on 3-fan units only). At condenser pressures
below 170 5 PSIG, the damper blades should be com-
pletely closed. As pressure rises above 170 5 PSIG, the
damper blades should begin opening and be fully open at
250 10 PSIG. Leaving the fuses in on fan 12 will prevent
head pressure from becoming excessive, since this fan will
start after the fully open setting of the damper operators
has been observed.
PART WINDING START (OPTIONAL)
Part winding
start is available on all voltage units and
consists of a solid state time delay wired in series with the
contactor that energizes the second winding of each com-
pressor motor. Its purpose is to limit current in-rush to the
compressors upon start-up. As each compressor starts, the
contactor for the first motor winding is energized instantly
while that for the second motor winding is delayed for 1
second.
Control checkout is best accomplished by observation as
each contactor is pulled in to see that the 1 second delay
occurs before the second contactor pulls in.
L I N E
N E U T R A L
PART WINDING
COMPRESSOR CONTACTOR
(2nd MOTOR WINDING)
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