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$er IV operation, there must be a thermostat call for the fan (G). This will move the damper to its mini- mum position during the occupied mode.
Above 50 F supply-air temperature, the dampers will modu- late from 100% open to the minimum open position. From 50 F to 45 F supply-air temperature, the dampers will main- tain at the minimum open position. Below 45 F the dampers will be completely shut. As the supply-air temperature rises, the dampers will come back open to the minimum open posi- tion once the supply-air temperature rises to 48 F.
If optional power exhaust is installed, as the outdoor-air damper opens and closes, the power exhaust fans will be energized and deenergized.
If field-installed accessory CO2 sensors are connected to the EconoMi$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 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.