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3.0 OPERATION
The standard range is 10°F [5.6°C]. To
determine the range of a condensing
unit, subtract the design no load return
air temperature (TNL) from the design
full load return air temperature (TFL) (R=
TFL- TNL). The standard range is 6°F
[3.3°C].
Set point of the opstat should be your
design leaving chilled water temperature
(TLW) for water chillers. The standard
adjustment range for AC units is 32 to
104°F [0° to 40°C].
The location of setting knob is shown in
Figure 3.7.2A.
Step Temp adjusts the temperature
range per stage in degrees F. To
determine TRB. For a standard
condensing unit TRB= 0.25 x R. Check
the dial setting on the opstat. The
approximate setting of Step Temp is
shown in the Figure 3.7.2B by the Step
Temp should be changed by an
authorized serviceman only.
3.8 ELECTRICAL CONTROLS
MCCB/MCB/MMS - Main Circuit Breaker
This is an automatic, calibrated, ambient
compensated, magnetic trip circuit breaker, which
provides both direct line-break compressor
branch circuit. short circuit locked rotor and
overload protection. It has a manually operable
handle for compressor circuit disconnect, and an
auxiliary NO. switch (optional) which interrupts the
115V compressor control circuit when the breaker
opens.
M - Contactor (Compressor and Fan
Motor)
The contactor, operated by the control circuit,
provides power individually to the compressor and
fan motors. Contactors are used either singly or in
parallel pairs for across-the-line start
(simultaneous operation). These devices are amp
rated to handle both rated load amp and locked
rotor amps.
CR - Relays (Miscellaneous Control)
These relays provide the necessary circuit logic
for lock-in, lock -out and transfer functions.
HTR - Crankcase Heater
Energized continuously as long as control circuit
power disconnect switch (not supplied with the
unit) is closed and compressor is off. This heater
maintains crankcase temperature above the
system temperature during the compressor off
cycle, preventing refrigerant migration into the
crankcase and consequent compressor damage.
SOL-
i.) Liquid Line Solenoid Valve
Closes when the compressor(s) is off to
prevent any liquid refrigerant from
accumulating in the chiller during the off
cycle.
ii.) Discharge Solenoid Control (Optional)
This function is used in low ambient
application. Discharge solenoid is turn off to
reduce condensing surface and to increase
head pressure.
OL - Motor Overload
(Manual Reset)
For AC the compressor is protected by overload
relays utilizing quick trip, ambient compensated
heaters. The overload relays are manually reset.
OUVR - Over Under Voltage Relay
(Optional)
Protects the unit from the following electric supply
malfunctions: over voltage, under voltage, please
reversal, single phasing and phase imbalance. If
the OUVR trips, a control relay will de-energize
and open the control circuit. A red LED trip light,
located on the OUVR, will indicate a supply
malfunction. Tile OUVR is a manual reset control
device.
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