Installation manual

035-16682-000-E-0303
Unitary Products Group 79
The proportional integral sequence controller (PI controller),
provides 13.9 VDC power from terminal “VDC” to each pres-
sure transducer. The transducer has an output signal of 0-10
VDC, which connects to the PI controller at terminal “SN”.
The PI controller regulates the output signal to the variable
frequency drive based on a fixed setpoint of 240 PSI. The
output signal from the PI controller is 4-20ma at the “I” termi-
nal. The input terminal on the variable frequency drive is the
“II” terminal. The PI controller will vary the output to maintain
a minimum discharge pressure of 240 PSI.
The Proportional Integral Sequence controller is factory set
for direct acting operation (the signal output increases as the
pressure signal increases). DIP switch setting is factory set
for C1 (switch 4 is in the ON position, all others are in the
OFF position). This is the fastest integration time available,
designed to compensate for extremely rapid rates of change.
The Throttling range is factory set to 20 PSIG factory set for
2VDC (20%) which is adjustable from 0 to 6VDC (0 to 60%).
NOTE: Altering the factory settings could result in poor con-
trol or operation of the system.
No special motor is required on the 208-230/460 volt units.
The 208-230 volt variable frequency drive requires single-
phase input power and it produces three-phase variable out-
put power to condenser fan motor #1. The 460-volt variable
frequency drive requires three-phase input power and pro-
duces three-phase variable output power to condenser fan
motor #1. On the 575-volt and 380-volt 60-hertz units a trans-
former is used to reduce line voltage to 230 volts.
The variable Frequency Drive is pre programmed at the fac-
tory and the keypad locked out.
SEQUENCE OF OPERATION - FOR HEAD
PRESSURE CONTROL
A call for the first stage cooling powers the 6M contactor
energizing the variable frequency drive. The drive will ramp to
the pre programmed minimum speed of 10 hertz immediately
upon start up. The drive is pre programmed for a minimum
speed of 10 hertz and a maximum speed of 60 hertz.
As the discharge pressure on system #1 or #2 compressor
rises above 240 PSI upon start up the PI controller will
increase the output signal to the variable frequency drive.
The drive will increase the speed of condenser #1 fan accord-
ingly.
The scroll compressor produces a rapid rise in discharge
pressure upon start up and this, usually will result in full
speed operation of condenser fan #1. After the discharge
pressure has settled out, the speed of condenser #1 may
decrease especially during times when the ambient tempera-
ture is below 80°F. After the #1 system has stabilized and
compressor #2 is energized, the speed of condenser Fan #1
will increase to compensate for the discharge pressure rise.
As the discharge pressure begins to fall below the 240-PSI
setpoint, the drive will reduce the speed of condenser fan #1.
As the ambient temperature drips below 40°F the #1 con-
denser fan will slow to the minimum speed. The #2 con-
denser fan will disengage when the discharge pressure drops
below 180 PSIG as the ambient temperature falls. The dis-
charge pressure of system #1 and/or #2 will increase when
condenser fan #2 stops consequently causing an increase in
the speed of condenser fan #1.
SERVICE
REFRIGERATION SYSTEM
CHARGE: Each system is fully factory charged with R-22.
The correct charge appears on the unit nameplate.
Thermal Expansion Valves: The 30 ton unit has 3 and the 40
ton unit has 4 independent refrigeration systems. These
TXVs are set to maintain 15°F superheat leaving the evapo-
rator coil. The superheat on each valve is adjustable, how-
ever, adjustments should only be made if absolutely
necessary.
MOISTURE/LIQUID SIGHT GLASS: Each system has a
moisture/liquid sight glass. These are located on the liquid
lines in the condenser section.
A clear flow of liquid indicates the unit is properly charged.
Any bubbles indicates the system is undercharged or non-
condensables may exist. Corrective action should be taken.
A change in color of the moisture indicator shows the approx-
imate moisture content of the system in parts per million. If
moisture is indicated, corrective action should be taken.
FILTER DRIER: Each system is equipped with a filter drier.
The drier should be replaced whenever moisture is indicated
in the system.
COMPRESSORS
Each compressor is inherently protected from over current
and over temperature. High and low pressure switches are
installed on the discharge and suction lines respectively for
high and low pressure protection. Scroll compressors operate
in only one direction. If the compressor is experiencing low
amperage draw, similar discharge and suction pressure or
increased noise level, it is operating in reverse. Switch two
line voltage connections to correct (See Compressor Rotation
page 61).