Bryant 558F, 551B, 551A manual CONTROLS cont, Sequence Of Operation Sizes

CONTROLS (cont)

Heating, Units Without Economizer — Upon a call for heating through terminal W1, indoor (evaporator) fan contactor (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.

Heating, Units With Economizer — When the room thermo- stat calls for heat through terminal W1, the indoor (evaporator) fan contactor (IFC) and heater contactor no. 1 (HC1) are ener- gized. 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 thermostat is satisfied, the damper moves to the fully closed position.

SEQUENCE OF OPERATION SIZES 155-300

Cooling, Units Without EconoMi$er — 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 motor, compressor no. 1, and condenser fans start. The condenser-fan motors run con- tinuously while unit is cooling. If the thermostat calls for a sec- ond stage of cooling by energizing Y2, compressor contactor no. 2 (C2) is energized and compressor no. 2 starts.

Heating, Units Without EconoMi$er (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.

Cooling, Units With EconoMi$er — When the OAT is above the ECON SP set point and the room thermostat calls for Stage 1 cooling (R to G + Y1), the indoor-fan motors (IFM) are energized and the EconoMi$er damper modulates to minimum position. The compressor contactor and OFC are energized to start 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 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: Compressors have a two-minute Minimum On and Mini- mum Off.

1.If Y1 is energized, and the room thermostat calls for Y2 (2-stage thermostat), the compressor and OFC are ener- gized. The position of the EconoMi$er damper is main- tained at its current value.

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 OFC are energized. The position of the EconoMi$er damper is maintained at its current value.

3.If Y1 is energized, and compressor no. 1 is already ener- gized (see Step 2) and the room thermostat calls for Y2,

compressor no. 1 continues to operate. If Y2 remains energized for more than 20 minutes, compressor no. 2 is energized.

NOTE: Compressor no. 2 cannot be energized unless there is a signal for Y2 from the space thermostat.

4.If compressor no. 2 is energized, and the Y2 signal from the thermostat is satisfied, compressors 1 and 2 are deener- gized. Re-asserting Y2 will start compressor no. 1 and (after a 20-minute interstage delay) compressor no. 2.

5.If compressor no. 1 is energized and the thermostat is satis- fied, compressor no. 1, 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.

Freeze Protection Thermostat(s) — A freeze protection ther- mostat (FPT) is located on the top and bottom of the evaporator coil. It detects frost build-up and turns off the compressor, allow- ing the coil to clear. Once frost has melted, the compressor can be reenergized by resetting the compressor lockout.

Heating, Units With EconoMi$er (If Accessory Heater is Installed) — When the room thermostat calls for heat, the heat- ing controls are energized as described in the Heating, Units Without EconoMi$er section. The IFM is energized and the EconoMi$er damper modulates to the minimum position. When the thermostat is satisfied, the damper modulates closed.

Units With Perfect Humidity™ Dehumidification Package — When thermostat calls for cooling, terminals G and Y1 and/or Y2 and the compressor contactor C1 and/or C2 are energized. The indoor (evaporator) fan motor (IFM), compressors, and out- door (condenser) fan motors (OFM) start. The OFMs run continuously while the unit is in cooling. As shipped from the factory, both Perfect Humidity dehumidification circuits are always energized.

If Perfect Humidity circuit modulation is desired, a field-installed, wall-mounted light-commercial thermidistat (with field-supplied relay) is required. If the thermidistat is installed and calls for the Perfect Humidity subcooler coil to operate, the relay switch closes. This energizes the 3-way liquid line solenoid valve coils (LLSV1 for circuit 1 and LLSV2 for circuit 2) of the Perfect Humidity circuits, forcing the warm liquid refrigerant of the liquid line to enter the subcooler coils.

As the warm liquid passes through the subcooler coils, it is exposed to the cold supply airflow coming off the evaporator coils and the liquid is further cooled to a temperature approach- ing the evaporator coil leaving-air temperature. The state of the refrigerant leaving the subcooler coils is a highly subcooled liquid refrigerant. The liquid then enters a thermostatic expan- sion valve (TXV) where the liquid is dropped to the evaporator pressure. The TXVs can throttle the pressure drop of the liquid refrigerant and maintain proper conditions at the compressor suction valves over a wide range of operating conditions. The liquid proceeds to the evaporator coils at a temperature lower than normal cooling operation. This lower temperature is what increases the latent and sensible capacity of the evapora- tor coils.

The 2-phase refrigerant passes through the evaporators and is changed into a vapor. The air passing over the evaporator coils will become colder than during normal operation as a result of the colder refrigerant temperatures. However, as it passes over the subcooler coils, the air will be warmed, decreasing the sen- sible capacity and reducing the sensible heat of the rooftop unit.

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