Heating; Service; Capacity Control (576C, 566D Units); Head Pressure Control (566D, 566E150-240 Units Only) - Bryant 566D Installation, Start-Up And Service Instructions Manual

refrigerant migration back to the compressor during the off
cycle.
C. 569F120 Cooling
When the thermostat calls for stage one cooling at start-up,
and all safety devices are satisfied, the compressor contactor
no. 1 (C1) energizes causing compressor no. 1 and outdoor-
fan motor no. 1 to start (the indoor-fan contactor should be
wired to start at the same time as the compressor). The liq-
uid line solenoid (LLS) valve will open when compressor
no. 1 starts, allowing refrigerant to flow in the system.
When the thermostat calls for stage two cooling, compressor
contactor no. 2 (C2) energizes causing compressor no. 2 and
outdoor-fan motor no. 2 to start. As the cooling demand
decreases, stage two on the thermostat opens, causing com-
pressor no. 2 and outdoor-fan motor no. 2 to shut down. As
the cooling continues to decrease, stage one of the thermo-
stat opens causing compressor no. 1 and outdoor-fan motor
no. 1 to shut down. The LLS valve for each compressor will
close when the associated compressor stops, minimizing the
potential for refrigerant migration during the off cycle.
The indoor-fan motor will stop if the thermostat is set to
AUTO and will continue to operate if the thermostat is set to
CONT. Each compressor is protected with a CLO device so
that the compressor will not operate if there is a high-
pressure fault, low pressure fault, or a compressor is off due
to internal line break overcurrent/over temperature protec-
tion. To reset the CLO device, set the thermostat higher to
remove the cooling demand, then return to the original set
point. This should be done only once. If the system shuts
down with the same fault, the cause for the fault should be
determined and corrected before the a CLO device is reset
again.
D. 566E150-240 Cooling
At start-up, when the thermostat calls for first stage cooling
and all safety devices are satisfied, the compressor contactor
(C1) energizes causing compressor no. 1 and fan motor no. 1
to start. Fan motor no. 2 will start when the fan cycling pres-
sure switch (FCPS) closes as discharge pressure builds. With
the indoor-fan contactor wired to TB2-4 and TB2-9 contacts
on the terminal block, the indoor-fan will also start with the
compressor. The liquid line solenoid (LLS) valve will open
when compressor no. 1 starts, allowing refrigerant to flow in
the system.
When the thermostat calls for stage two cooling, compressor
contactor no. 2 (C2) energizes causing compressor no. 2 to
start. As the cooling demand decreases, stage two on the
thermostat opens, causing compressor no. 2 to shut down. As
the cooling continues to decrease, stage one of the thermo-
stat opens causing compressor no. 1 and outdoor-fan motor
to shut down. The LLS valve for each compressor will close
when the associated compressor stops, minimizing the
potential for refrigerant migration during the off cycle.
The indoor-fan motor will stop if the thermostat is set to
AUTO and will continue to operate if the thermostat is set on
CONT. Each compressor is controlled by the thermostat so
they will not start until there is a demand from the thermo-
stat. Each compressor is protected with a CLO device so that
the compressor will not operate if there is a high-pressure
fault, low-pressure fault, or compressor is off due to internal
line break overcurrent/overtemperature protection. To reset
the a CLO device, set the thermostat higher to remove the
cooling demand, then return to the original set point. This
should be done only once. If the system shuts down with the
same fault, the cause for the fault should be determined and
corrected before the a CLO device is reset again.
II. HEATING
The heating thermostat (TH) energizes a field-supplied relay
which operates heating controls and energizes the indoor
unit relay. When the fan switch is set at AUTO, the indoor
unit fan cycles with the heating control. The indoor unit fan
runs continuously when the fan switch is set at ON.
Causes of complete unit shutdown are: interruption of
supplied power, open compressor internal protector (IP),
open control circuit breaker, or an open high-pressure or
low-pressure safety switch.
I. CAPACITY CONTROL (576C, 566D UNITS)
A suction pressure-actuated unloader controls 2 cylinders
and provides capacity control. Unloaders are factory set (see
Tables 1A-1C), but can be field adjusted as described in the
next paragraphs.
Control set point (cylinder load point) is adjustable from 0 to
85 psig (586 kPa). To adjust, turn control set point
adjustment nut (Fig. 20) clockwise to its bottom stop. In this
position, set point is 85 psig. Next, turn adjustment counter-
clockwise to desired control set point. Every full turn
counterclockwise decreases set point by 7.5 psig.
Pressure differential (difference between cylinder load and
unload points) is adjustable from 6 to 22 psig. To adjust, turn
pressure differential adjustment screw (Fig. 20) counterclock-
wise to its back stop position. In this position, differential is
6 psig. Next, turn adjustment clockwise to desired pressure
differential setting. Every full turn clockwise increases differ-
ential by 1.5 psig.
II. HEAD PRESSURE CONTROL (566D, 566E150-240 UNITS
ONLY)
Fan cycling is a standard feature. The no. 2 fan cycles in
response to changes in liquid pressure. The switch cycles the
fan off at 160 ± 10 psig as pressure decreases, and cycles it
back on at 255 ± 10 psig.
Fig. 20 — Compressor Capacity Control Unloader
— —
21

SERVICE