Operating Sequence

Heating — To start the unit, turn on the main power supply.

Set the thermostat at HEAT position at a setting above room temperature, the fan at AUTO position.

The first stage of the thermostat energizes the indoor-fan motor, compressor, and outdoor fan; the second stage energizes electric heater elements, if installed. Check the heating effects at the air supply grille(s).

If the accessory electric heaters do not energize, reset limit switch (located on indoor-fan scroll) by pressing the button located between terminals on the switch.

TO SHUT OFF UNIT — Set the system selector switch at OFF position. Resetting the heating selector lever below room temperature temporarily shuts the unit off until the space temperature falls below the thermostat setting.

Safety Relief — A soft solder joint on the suction line at the loss-of-charge/low-pressure fitting provides pressure relief under abnormal temperature and pressure conditions.

Ventilation (Continuous Fan) — Set the fan and system selector switches at ON and OFF positions, respectively. The in- door fan operates continuously to provide constant air circulation.

COOLING, UNITS WITHOUT ECONOMIZER — When thermostat calls for cooling, terminals G and Y1 are energized. The indoor-fan contactor (IFC), reversing valve solenoid (RVS1) and compressor contactor no. 1 (C1) are energized and indoor-fan motor, compressor no. 1, and outdoor fan starts. The outdoor-fan motor(s) run continuously while unit is cooling. If the thermostat calls for a second stage of cooling by energizing Y2, compressor contactor no. 2 (C2) and reversing valve sole- noid (RVS2) are energized and compressor no. 2 starts.

HEATING, UNITS WITHOUT ECONOMIZER — Upon a request for heating from the space thermostat, terminal W1 will be energized with 24 v. The IFC, outdoor-fan contactor (OFC), C1, and C2 will be energized. The reversing valves switch po- sition and the indoor fan, outdoor fan, compressor no. 1, and compressor no. 2 are energized.

If the space temperature continues to fall while W1 is ener- gized, W2 will be energized with 24 v, and the heater contac- tor(s) (HC) will be energized, which will energize the electric heater(s).

When the space thermostat is satisfied, W2 will be deener- gized first, and the electric heater(s) will be deenergized.

Upon a further rise in space temperature, W1 will be deenergized, and the reversing valve solenoids (RVS1 and RVS2) will be energized.

COOLING, UNITS WITH ECONOMI$ER IV — When free cooling is not available, the compressors will be controlled by the zone thermostat. When free cooling is available, the outdoor-air damper is modulated by the EconoMi$er IV con- trol 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 modulated (open or close) to bring the supply-air temperature back within 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 minimum 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 maintain at the minimum open position. Below 45 F the dampers will be completely shut. As the supply-air temperature rises, the damp- ers will come back open to the minimum open position 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 ener- gized and deenergized.

If field-installed accessory CO2 sensors are connected to the EconoMi$er IV control, a demand controlled ventilation strate- gy 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 high- er 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 cooling (Y1 closes at the thermostat) will cause the control to modulate the dampers open to maintain the supply-air temperature 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.

HEATING, UNITS WITH ECONOMI$ER IV — When the room temperature calls for heat, the heating controls are ener- gized as described in the Heating, Units Without Economizer section. When the thermostat is satisfied, the economizer damper moves to the minimum position.

COOLING, UNITS WITH ECONOMI$ER2, PREMIER- LINK™ CONTROL AND A THERMOSTAT — When free cooling is not available, the compressors will be controlled by the PremierLink control in response to the Y1 and Y2 inputs from the thermostat.

The PremierLink control will use the following information to determine if free cooling is available:

•Indoor fan has been on for at least 30 seconds.

•The SPT, SAT, and OAT inputs must have valid readings.

•OAT must be less than 75 F.

•OAT must be less than SPT.

•Enthalpy must be LOW (may be jumpered if an enthalpy sensor not available).

•Economizer position is NOT forced.

Pre-cooling occurs when the is no call from the thermostat except G. Pre-cooling is defined as the economizer modulates to provide 70 F supply air.

When free cooling is available the PremierLink control will control the compressors and economizer to provide a supply- air temperature determined to meet the Y1 and Y2 calls from the thermostat using the following three routines. The three control routines are based on OAT, where:

SASP = Supply Air Set Point

DXCTLO = Direct Expansion Cooling Lockout Set Point Routine 1 — (OAT < DXCTLO)

•Y1 energized — economizer maintains a SASP = (SATLO1 + 3).

•Y2 energized — economizer maintains a SASP = (SATLO2 + 3).

Routine 2 — (DXCTLO < OAT < 68 F)

•If only Y1 energized, the economizer maintains a SASP = (SATLO1 + 3).

•If SAT > SASP + 5 and economizer position > 80%, economizer will go to minimum position for 3 minutes or until SAT > 68 F.

•First stage of mechanical cooling will be energized.

•Integrator resets.

•Economizer opens again and controls to current SASP after stage one on for 90 seconds.

•With Y1 and Y2 energized Economizer maintains an SASP = SATLO2 + 3.