HEATING, UNITS WITHOUT ECONOMIZER — When the thermostat calls for heating, terminal 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. 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 out- door-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 move 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$ER — When the Outdoor Air Temperature (OAT) is above the ECON SP set point and the room thermostat calls for Stage 1 cooling (R to G +Y1), the indoor-fan motor (IFM) is energized and the EconoMi$er damper modulates to minimum position. The compressor contactor is energized starting the compressor and outdoor-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 set point 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$er modulates open, allowing a greater amount of outdoor air to enter the unit. If the SAT drops below 53 F, the outdoor-air damper modules closed to reduce the amount of outdoor air. When the SAT is between 53 and 57 F, the EconoMi$er maintains its position.
HEATING, UNITS WITH ECONOMIZER — When the ther- mostat calls for heating, terminal 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 and the damper moves to the minimum position. When additional heat is need- ed, W2 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. The economizer damper then moves to the fully closed position. When using continuous fan, the damper will remain in the minimum position.
UNITS WITH MOISTUREMISER DEHUMIDIFICATION PACKAGE — When thermostat calls for cooling, terminals G and Y1 and the compressor contactor C1 is energized. The in- door (evaporator) fan motor (IFM), compressor, and outdoor (condenser) fan motor (OFM) start. The OFM runs continuous- ly while the unit is in cooling. As shipped from the factory, MoistureMiser dehumidification circuit is always energized. If MoistureMiser circuit modulation is desired, a field-installed, wall-mounted humidistat is required.
If the MoistureMiser humidistat is installed and calls for the MoistureMiser subcooler coil to operate, the humidistat inter- nal switch closes. This energizes and closes the liquid line sole- noid valve coil (LLSV) of the MoistureMiser circuit, forcing the hot liquid refrigerant of the liquid line to enter the subcooler coil (see Fig. 39). As the hot liquid passes through the subcool- er coil, it is exposed to the cold supply airflow coming off from the evaporator coil and the liquid is further cooled to a temper- ature approaching the evaporator coil leaving-air temperature. The state of the refrigerant leaving the subcooler coil is a high- ly subcooled liquid refrigerant. The liquid then enters a thermo- static expansion valve (TXV) where the liquid is dropped to a lower pressure. The TXV does not have a pressure drop great enough to change the liquid to a 2-phase fluid. The TXV can throttle the pressure drop of the liquid refrigerant and maintain proper conditions at the compressor suction valve over a wide range of operating conditions. The liquid then enters a second fixed restrictor expansion device for a second pressure drop to a 2-phase fluid. The liquid proceeds to the evaporator coil at a temperature lower than normal cooling operation. This lower temperature is what increases the latent capacity of the rooftop. The 2-phase refrigerant passes through the evaporator and is changed into a vapor. The air passing over the evaporator coil will become colder than during normal operation as a result of the colder refrigerant temperatures. However, as it passes over the subcooler coil, the air will be warmed slightly.
As the refrigerant leaves the evaporator, the refrigerant passes a low-pressure switch in the suction line. This low- pressure switch will de-activate the MoistureMiser package when the suction pressure reaches 60 psig. The low-pressure switch is an added safety device to protect against evaporator coil freeze-up. The low-pressure switch will only de-activate and open the liquid line solenoid valve in the MoistureMiser circuit. The compressors will continue to run as long as there is a call for cooling, regardless of the position of the low-pressure switch. The solenoid valve and the MoistureMiser package will be re-activated only when the call for cooling has been satis- fied, the low-pressure switch has closed, and a new call for cooling exists. The crankcase heaters on the scroll compressor provide additional protection for the compressor due to the ad- ditional refrigerant charge in the subcooler.
When the humidistat is satisfied, the humidistat internal switch opens cutting power to and opening the LLSV. The re- frigerant is routed back through the evaporator and the sub- cooler coil is removed from the refrigerant loop.
When the thermostat is satisfied, C1 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 IFM will run continuously.
