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2. Energize the compressor.
3. The suction pressure should drop and the discharge
pressure should rise, as is normal on any start-up.
If the suction pressure does not drop and the discharge pres-
sure does not rise to normal levels:
1. Note that the evaporator fan is probably also rotating
in the wrong direction.
2. Turn off power to the unit, tag disconnect.
3. Reverse any two of the unit power leads.
4. Turn on power to the unit.
The suction and discharge pressure levels should now move
to their normal start-up levels.
NOTE: When the compressor is rotating in the wrong direc-
tion, the unit makes an elevated level of noise and does not
provide cooling.
VIII. COOLING
To start unit, turn on main power supply. Set system selector
switch at COOL position and fan switch at AUTO. position.
Adjust thermostat to a setting below room temperature.
Compressor starts on closure of contactor.
Check unit charge. Refer to Refrigerant Charge section on
page 57. Unit must operate a minimum of 10 minutes before
adjusting charge.
Reset thermostat at a position above room temperature.
Compressor will shut off.
A. To Shut Off Unit
Set system selector switch at OFF position. Resetting thermo-
stat at a position above room temperature shuts unit off tem-
porarily until space temperature exceeds thermostat setting.
IX. HEATING (If Accessory Electric Heater is Installed)
To start unit, turn on main power supply.
Set thermostat at HEAT position and a setting above room
temperature, and set fan at AUTO. position.
First stage of thermostat energizes the first-stage electric
heater; second stage energizes second-stage electric heater
elements, if installed. Check air supply grille(s) to ensure
proper heat supply.
If unit does not energize, reset limit switch (located on
evaporator-fan scroll) by pressing button located between
terminals on the switch.
A. To Shut Off Unit
Set system selector switch at OFF position. Resetting heat-
ing selector lever below room temperature will shut unit off
temporarily until space temperature falls below thermostat
setting.
X. SAFETY RELIEF
A soft solder joint in the suction line at the low-pressure
service port provides pressure relief under abnormal temper-
ature and pressure conditions.
XI. VENTILATION (Continuous Fan)
Set fan and system selector switches at ON and OFF posi-
tions, respectively. Evaporator fan operates continuously to
provide air circulation.
XII. OPERATING SEQUENCE
A. Cooling, Units Without EconoMi$er IV
When thermostat calls for cooling, terminals G and Y1 are
energized. The indoor (evaporator) fan contactor (IFC) and
compressor contactor no. 1 (C1) are energized, and
evaporator-fan motors, compressor no. 1, and condenser fans
start. The condenser-fan motor runs continuously while unit
is cooling. For units with 2 stages of cooling, if the thermostat
calls for a second stage of cooling by energizing Y2, compres-
sor contactor no. 2 (C2) is energized and compressor no. 2
starts.
When the thermostat is satisfied, C1 and C2 are deenergized
and the compressors and outdoor (condenser) fan motors
(OFM) shut off. After a 30-second delay, the indoor (evapora-
tor) fan motor (IFM) shuts off. If the thermostat fan selector
switch is in the ON position, the evaporator motor will run
continuously.
B. Heating, Units Without EconoMi$er IV (If Optional or
Accessory Heater is Installed)
Upon a call for heating through terminal W1, IFC and
heater contactor no. 1 (HC1) are energized. On units
equipped for 2 stages of heat, when additional heat is needed
HC2 is energized through W2.
C. Cooling, Units With EconoMi$er IV
When free cooling is not available, the compressors will be
controlled by the zone thermostat. When free cooling is avail-
able, the outdoor-air damper is modulated by the
EconoMi$er IV control to provide a 50 to 55 F supply-air
temperature into the zone. As the supply-air temperature
fluctuates above 55 or below 50 F, the dampers will be modu-
lated (open or close) to bring the supply-air temperature
back within set points limits.
For EconoMi$er IV operation, there must be a thermostat
call for the fan (G). This will move the damper to its mini-
mum position during the occupied mode.
Above 50 F supply-air temperature, the dampers will modu-
late from 100% open to the minimum open position. From
50 F to 45 F supply-air temperature, the dampers will main-
tain at the minimum open position. Below 45 F the dampers
will be completely shut. As the supply-air temperature rises,
the dampers will come back open to the minimum open posi-
tion once the supply-air temperature rises to 48 F.
If optional power exhaust is installed, as the outdoor-air
damper opens and closes, the power exhaust fans will be
energized and deenergized.
If field-installed accessory CO
2
sensors are connected to the
EconoMi$er IV control, a demand controlled ventilation
strategy will begin to operate. As the CO
2
level in the zone
increases above the CO
2
set point, the minimum position of
the damper will be increased proportionally. As the CO
2
level
decreases because of the increase in fresh air, the outdoor-air
damper will be proportionally closed. Damper position will
follow the higher demand condition from DCV mode or free
cooling mode.
Damper movement from full closed to full open (or vice
versa) will take between 1
1
/
2
and 2
1
/
2
minutes.
If free cooling can be used as determined from the appropri-
ate changeover command (switch, dry bulb, enthalpy curve,
differential dry bulb, or differential enthalpy), a call for cool-
ing (Y1 closes at the thermostat) will cause the control to
modulate the dampers open to maintain the supply air tem-
perature set point at 50 to 55 F.
As the supply-air temperature drops below the set point range
of 50 to 55 F, the control will modulate the outdoor-air damp-
ers closed to maintain the proper supply-air temperature.
D. Heating, Units With EconoMi$er IV
When the room temperature calls for heat, the heating
controls are energized as described in the Heating, Units
Without EconoMi$er IV section. When the thermostat is
satisfied, the economizer damper moves to the minimum
position.