Bryant DuraPac 558F Installation & Service Instructions Manual page 25

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 deenergized. Re-asserting Y2 will start compres-
sor no. 1 and (after a 20-minute interstage delay)
compressor no. 2.
5. If compressor no. 1 is energized and the thermostat is
satisfied, compressor no. 1, the OFM, and IFM are
deenergized and the EconoMi$er modulates closed.
When the OAT is below the MECH CLG LOCKOUT set
point, the compressors remain off.
D. Freeze Protection Thermostat(s)
A freeze protection thermostat (FPT) is located on the top
and bottom of the evaporator coil. It detects frost build-up
and turns off the compressor, allowing the coil to clear. Once
frost has melted, the compressor can be reenergized by reset-
ting the compressor lockout.
E. Heating, Units with EconoMi$er (If Accessory or
Optional Heater is Installed)
When the room thermostat calls for heat, the heating 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 ther-
mostat is satisfied, the damper modulates closed.
F. 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 ener-
gized. The indoor (evaporator) fan motor (IFM), compressors,
and outdoor (condenser) fan motors (OFM) start. The OFMs
run continuously while the unit is in cooling. As shipped
Fig. 32 — Perfect Humidity Operation Diagram (Single Circuit Shown)
from the factory, both Perfect Humidity dehumidification cir-
cuits are always energized.
If Perfect Humidity circuit modulation is desired, a field-
installed, wall-mounted humidistat or light commercial ther-
midistat is required. If the Perfect Humidity control is
installed and calls for the Perfect Humidity subcooler coil to
operate, the control 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 refrig-
erant of the liquid line to enter the subcooler coils. See
Fig. 32.
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
approaching 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 expansion 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 evaporator 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 sensible capacity and reducing the sensible
heat of the roof-top unit.
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