If the limit switch trips at the start of the heating cycle dur- ing the evaporator ON delay, the time period of the ON delay for the next cycle will be 5 seconds less than the time at which the switch tripped. (Example: If the limit switch trips at 30 sec- onds, the evaporator-fan ON delay for the next cycle will occur at 25 seconds.) To prevent short-cycling, a 5-second reduction will only occur if a minimum of 10 minutes has elapsed since the last call for heating.
The evaporator-fan OFF delay can also be modified. Once the call for heating has ended, there is a 10-minute period dur- ing which the modification can occur. If the limit switch trips during this period, the evaporator-fan OFF delay will increase by 15 seconds. A maximum of 9 trips can occur, extending the evaporator-fan OFF delay to 180 seconds.
To restore the original default value, reset the power to the unit.
TO SHUT OFF UNIT — Set system selector switch at OFF position. Resetting heating selector lever below room tempera- ture will temporarily shut unit off until space temperature falls below thermostat setting.
Safety Relief — A soft solder joint at the suction service Schrader port provides pressure relief under abnormal tempera- ture and pressure conditions (i.e., fire in building).
Ventilation (Continuous Fan) — Set fan and system selector switches at ON and OFF positions, respectively. Evap- orator fan operates continuously to provide constant air circula- tion. When the evaporator-fan selector switch is turned to the OFF position, there is a 30-second delay before the fan turns off.
Operating Sequence
COOLING, UNITS WITHOUT ECONOMIZER — When thermostat calls for cooling, terminals G and Y1 are energized, and the indoor (evaporator) fan motor (IFM), compressor, and outdoor (condenser) fan motor (OFM) start. The OFM runs continuously while the unit is in cooling. When the thermostat is satisfied, compressor contactor (C) is deenergized and the compressor and OFM shut off. After a 30-second delay, the IFM shuts off. If the thermostat fan selector switch is in the ON position, the evaporator motor will run continuously.
HEATING, UNITS WITHOUT ECONOMIZER — When the thermostat calls for heating, terminal W1 is energized. To prevent thermostat short-cycling, the unit is locked into the Heating mode for at least 1 minute when W1 is energized. The induced-draft motor is energized and the burner ignition se- quence begins. The indoor (evaporator) fan motor (IFM) is en- ergized 45 seconds after a flame is ignited. On units equipped for two stages of heat, when additional heat is needed, W2 is energized and the high-fire solenoid on the main gas valve (MGV) is energized. When the thermostat is satisfied and W1 is deenergized, the IFM stops after a 45-second time-off delay.
COOLING, UNITS WITH DURABLADE ECONO- MIZER — When the outdoor-air temperature is above the outdoor-air thermostat (OAT) setting and the room thermostat calls for cooling, compressor contactor is energized to start compressor and the outdoor (condenser) fan motor (OFM). The indoor (evaporator) fan motor (IFM) is energized and the economizer damper moves to the minimum position. After the thermostat is satisfied, there is a 30-second delay before the evaporator fan turns off. The damper then moves to the fully closed position. When using continuous fan, the damper moves to the minimum position.
When the outdoor-air temperature is below the OAT setting and the thermostat calls for cooling, the economizer damper moves to the minimum position. If the supply-air temperature is above 57 F, the damper continues to open until it reaches the
fully open position or until the supply-air temperature drops below 52 F.
When the supply-air temperature falls between 57 F and
52 F, the damper will remain at an intermediate open position. If the supply-air temperature falls below 52 F, the damper will modulate closed until it reaches the minimum position or until the supply air temperature is above 52 F. When the thermostat is satisfied, the damper moves to the fully closed position when using AUTO. fan or to the minimum position when using con- tinuous fan.
If the outdoor air alone cannot satisfy the cooling require- ments of the conditioned space, economizer cooling is integrat- ed with mechanical cooling, providing two stages of cooling. Compressor and the condenser fan will be energized and the position of the economizer damper will be determined by the supply-air temperature. When the second stage of cooling is satisfied, the compressor and OFM will be deenergized. The damper position will be determined by the supply-air tempera- ture. When the first stage of cooling is satisfied, there is a 30-second delay before the evaporator fan shuts off. The damp- er then moves to the fully closed position. When using a con- tinuous fan, the damper moves to the minimum position.
COOLING, UNITS WITH ECONOMI$ER — When the outdoor-air temperature (OAT) is above the ECON SP set point and the room thermostat calls for Stage 1 cooling (R to G + Y1), the indoor (evaporator) fan motor (IFM) is energized and the EconoMi$er damper modulates to minimum position. The compressor contactor is energized to start the compressor and outdoor (condenser) fan motor (OFM). After the thermostat is satisfied, the damper modulates to the fully closed position when the IFM is deenergized.
When the OAT is below the ECON SP setting and the room thermostat calls for Stage 1 cooling (R to G + Y1), the EconoMi$er modulates to the minimum position when the IFM is energized. The EconoMi$er provides Stage 1 of cooling by modulating the return and outdoor air dampers to maintain a 55 F supply air set point. If the supply-air temperature (SAT) is greater than 57 F, the EconoMi$er modulates open, allowing a greater amount of outdoor air to enter the unit. If the SAT drops below 53 F, the outdoor air damper modulates closed to reduce the amount of outdoor air. When the SAT is between 53 and 57 F, the EconoMi$er maintains its position.
If outdoor air alone cannot satisfy the cooling requirements of the conditioned space, and the OAT is above the MECH CLG LOCKOUT set point, the EconoMi$er integrates free cooling with mechanical cooling. This is accomplished by the strategies below.
NOTE: Compressor has a 2-minute Minimum On, Minimum Off, and Interstage delay timer.
1.If Y1 is energized, and the room thermostat calls for Y2 (2-stage thermostat), the compressor and OFM are ener- gized. The EconoMi$er damper is maintained at its cur- rent position.
2.If Y1 is energized for more than 20 minutes, and Y2 is not energized (whether or not a 2-stage thermostat is used), the compressor and OFM are energized. The EconoMi$er damper is maintained at its current position.
3.If Y1 is energized, and the compressor is already ener- gized (see Step 2) and the room thermostat calls for Y2, the compressor contains to operate.
4.If the compressor is energized and the thermostat is satis- fied, the compressor, the OFM, and IFM are deenergized and the EconoMi$er modulates closed.
When the OAT is below the MECH CLG LOCKOUT set point, the compressors remain off.
