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530.18-N6Y
COOLING SYSTEM
The cooling section is a complete factory package utilizing an
air-cooled condenser. The system is factory-charged with
Refrigerant-22.
The compressors are hermetically sealed, internally sprung
and base mounted with rubber insulated hold-down bolts.
Compressors have inherent (internal protection. If there is an
abnormal temperature rise in compressor, the protector will
open to shut down the compressor.
PRELIMINARY OPERATION COOLING
After installation has been completed, energize the crankcase
heaters for at lest four hours before operation the unit. After the
initial installation, the compressors should be given three false
starts (energized just long enough to make a few revolutions
with 5-7 minutes delay between each start, before being put
into full time service.
COOLING SEQUENCE OF OPERATION
NO OUTDOOR AIR OPTIONS - When the room thermostat
calls for "first-stage" cooling, the low voltage control circuit from
"R" to "G" and "Y1" is completed to energize compressor #1,
condenser fan motor #1, condenser fan motor #2 (if the ambient
temperature is above 60°F), and the supply air blower motor (if
the fan switch on the room thermostat is set in the "AUTO"
position).
When the thermostat calls for "second-stage" cooling, the low
voltage control circuit from "R" to "Y2" is completed to energize
compressor #2.
After the thermostat is satisfied and opens, all components will
stop simultaneously. The blower motor will continue to operate
if the fan switch on the room thermostat is set in the "ON"
position.
ECONOMIZER WITH SINGLE ENTHALPY SENSOR - When
the room thermostat calls for "first-stage" cooling, the low
voltage control circuit from "R" to "G" and "Y1" is completed.
The "R" to "G" circuit energizes the blower motor (if the fan
switch on the room thermostat is set in the "AUTO" position)
and drives the economizer dampers from fully closed to their
minimum position. If the enthalpy of the outdoor air is below the
setpoint of the enthalpy controller (previously determined), "Y1"
energizes the economizer. The dampers will modulate to
maintain a constant supply air temperature as monitored by the
discharge air sensor. If the outdoor air enthalpy is above the
setpoint, "Y1" energizes compressor #1, condenser fan motor
#1, and condenser fan motor #2 (if the ambient temperature is
above 60°F).
When the thermostat calls for "second-stage" cooling, the low
voltage control circuit from "R" to "Y2" is completed. If the
enthalpy of the outdoor air is below the setpoint of the enthalpy
controller (i.e. first stage has energized the economizer), "Y2"
will energize compressor #1. If the outdoor air is above the
setpoint, "Y2" will energize compressor #2.
After the thermostat is satisfied and opens, all components will
stop simultaneously. The blower motor will continue to operate
if the fan switch on the room thermostat is set in the "ON"
position.
ECONOMIZER WITH DUAL ENTHALPY SENSORS - The
operation with the dual enthalpy sensors is identical to the
single sensor except that a second enthalpy sensor is mounted
in the return air. This return air sensor allows the economizer
to choose between outdoor air and return air, whichever has
the lowest enthalpy value, to provide maximum operating
efficiency.
16
OPERATION
ECONOM IZER (SINGLE OR DUAL) WITH POWER
EXHAUST - This system operates as specified above with one
addition. The power exhaust motor is energized whenever the
economizer is chosen by the enthalpy sensor for first stage
cooling, "Y1". As always, the "R" to "G" connection provides
minimum position but does not provide power exhaust
operation.
MOTORIZED OUTDOOR AIR DAMPERS - This system
operation is the same as the units with no outdoor air options
with one exception. When the "R" to "G" circuit is complete, the
motorized damper drives open to a position set by the
thumbwheel on the damper motor. When the "R" to "G" circuit
is opened, the damper spring returns fully closed.
CONTINUOUS BLOWER - Continuous blower operation is
possible by closing the R to G circuit on the thermostat.
SAFETY CONTROLS
Each refrigerant system is equipped with the following safety
controls:
1. A Suction Line Freezestat to protect against low evaporator
temperatures due to a low air flow or a low return air
temperature. (Opens at 26°F +5° F and resets at 38°F +
5°F.)
2. A High Pressure Cutout Switch to protect against excessive
discharge pressures due to a blocked condenser coil or a
condenser motor failure. (Opens at 380 psig + 10 and resets
at 300 psig + 10.)
3. A Low Pressure Switch to protect against loss of refrigerant
charge. (Opens at 7 psiog + 3 and resets at 22 psig + 5.)
If either one of the above safety controls opens, that individual
refrigerant system will be locked out. The other refrigerant
system will continue in operation unless it too is effected by the
same fault. The lock out of either system can be reset by
opening the 24V circuit either at the room thermostat or at the
unit disconnect.
HEATING SYSTEM
The following sequence describes the operation of the gas heat
section.
CONTINUOUS BLOWER
With the room thermostat switch set to "ON", the supply air
blower will operate continuously. The normally closed contact
"K5-1" provides 24 volt power to the "3M" contactor. The "3M-1,
2 & 3" power contacts close and the blower motor operates.
INTERMITTENT BLOWER
With the room thermostat system switch set to the "AUTO" or
"HEAT" position and the fan switch set to "AUTO", the supply
air blower will operate after the room thermostat calls for heat
and the time delay relay closes.
The "TH1" closes, the heat relay "RW1" is energized. The
"RW1-1" power contact closes energizing the line voltage draft
motor. The "RW1-2" contact is also closed. As the speed of the
draft motor reaches approximately 2500 RPM, the centrifugal
switch contact located on the end of the draft motor shaft closes
to power the first stage ignition module "IC1".
Ignition module "IC1" will immediately start the first stage ignitor
sparking and will open the redundant valve located inside the
first stage main gas valve "GV1" to allow a flow of gas to only
the first stage carryover tube. Only after the pilot flame has been
ignited and the presence of pilot flame detected at the "IC1" by
a signal sent back through the flame sensor is sparking
terminated and the first stage main gas valve opened.
Gas flows into each of the main burners and is ignited from the
carryover tube flame.
If "IC1" fails to detect a pilot flame, it will continue to try for a
maximum of 85 seconds to ignite the pilot tube. If the pilot flame
is not detected, then "IC1" will lock out first stage furnace
Unitary Products Group
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