IX. 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 42.
Reset thermostat at a position above room temperature. Compressor will shut off.
To Shut Off Unit
Set system selector switch at OFF position. Resetting ther- mostat at a position above room temperature shuts unit off temporarily until space temperature exceeds thermostat set- ting. Units are equipped with Cycle-LOC™ protection device. Unit shuts down on any safety trip and remains off; an indicator light on the thermostat comes on. Check reason for safety trip.
Compressor restart is accomplished by manual reset at the thermostat by turning the selector switch to OFF position and then ON position.
X. HEATING (IF ACCESSORY 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 elements; second stage energizes second-stage electric heater elements. Check heating effects at air supply grille(s).
If accessory electric heaters do not energize, reset limit switch (located on evaporator-fan scroll) by pressing button located between terminals on the switch.
To Shut Off Unit
Set system selector switch at OFF position. Resetting heating selector lever below room temperature temporarily shuts unit off until space temperature falls below thermostat setting.
XI. SAFETY RELIEF
Asoft solder joint in the suction line at the loss-of-charge/ low-pressure switch fitting provides pressure relief under abnormal temperature and pressure conditions.
XII. VENTILATION (CONTINUOUS FAN)
Set fan and system selector switches at ON and OFF posi- tions, respectively. Evaporator fan operates continuously to provide constant air circulation.
XIII. OPERATING SEQUENCE
A. Cooling, Units Without EconoMi$er IV
When the thermostat calls for cooling, terminals G and Y1 are energized. The indoor (evaporator) fan contactor (IFC), outdoor (condenser) fan contactor (OFC), and compressor contactor no. 1 (C1) are energized and the evaporator-fan motor, compressor no. 1, and condenser fans start. The condenser-fan motors run continuously while unit is in cool- ing. If the thermostat calls for a second stage of cooling by energizing Y2, compressor contactor no. 2 (C2) is energized and compressor no. 2 starts.
B.Heating, Units Without EconoMi$er IV (If 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 the set point limits.
For EconoMi$er IV operation, there must be a thermostat call for the fan (G). This will move the damper to its mini- mum position during the occupied mode.
Above 50 F supply-air temperature, the dampers will modu- late from 100% open to the minimum open position. From 50 F to 45 F supply-air temperature, the dampers will main- tain at the minimum open position. Below 45 F the dampers will be completely shut. As the supply-air temperature rises, the dampers will come back open to the minimum open posi- tion once the supply air temperature rises to 48 F.
If optional power exhaust is installed, as the outdoor-air damper opens and closes, the power exhaust fans will be energized and deenergized.
If field-installed accessory CO2 sensors are connected to the EconoMi$er IV control, a demand controlled ventilation strategy will begin to operate. As the CO2 level in the zone increases above the CO2 set point, the minimum position of the damper will be increased proportionally. As the CO2 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 11/2 and 21/2 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 dampers closed to maintain the proper supply-air temperature.
D. Heating, Units with EconoMi$er IV
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. The economizer damper moves to the minimum position. When the thermo- stat is satisfied, the damper moves to the fully closed position.
E. Units With Perfect Humidity™ Dehumidification System
Normal Design Cooling Operation
When the rooftop operates under the normal sequence of operation, the compressors will cycle to maintain indoor con- ditions. See Fig. 40.
The Perfect Humidity dehumidification system includes a factory-installed Motormaster® low ambient control to keep the head and suction pressure high, allowing normal design cooling mode operation down to 0° F.