Bryant 541A - Manual (Page 13)

V. CHECK HEATING CYCLE OPERATION
Place thermostat selector switch at HEAT and reset the space
set point above ambient temperature so that a call for heat-
ing is ensured. Compressor will start within 5 minutes. Ob-
serve system operation.
VI. CHECK COMPRESSOR OIL LEVEL
After adjusting the refrigerant charge, allow the system to
run fully loaded for 20 minutes. Running oil level should be
within view in the crankcase sight glass. Stop the compres-
sor at the field power supply disconnect and check the crank-
case oil level. Add oil only if necessary to bring the oil into
view in the sight glass. If oil is added, run the system for an
additional 10 minutes, then stop and check oil level. If the
level remains low, check the piping system for proper design
for oil return; also check the system for leaks.
If the initial check shows too much oil (too high in the sight
glass) remove oil to proper level. See Preliminary Oil Charge,
page 12, for proper procedure for adding and removing oil.
When the above checks are complete, repeat the procedure
with the unit operating at minimum load conditions.
Unload the compressor by disconnecting the field-control
Y2 circuit lead at TB2 .
Reconnect the field-control circuit lead when checks are
complete.
VII. FINAL CHECKS
Ensure all safety controls are operating, control panel covers
are on, and the service panels are in place.
VIII. SEQUENCE OF OPERATION
A. Heating
Place thermostat selector at HEAT and set temperature se-
lector above room ambient.
B. Cooling
Place thermostat selector at COOL and set temperature se-
lector below room ambient.
When thermostat calls for unit operation (either heating or
cooling), the indoor-fan motor starts immediately. The outdoor-
fan motors and compressor start within 3 seconds to 5 min-
utes depending on when unit was last shut off by thermostat,
because unit contains a Time Guard
௡ circuit. When first-
stage cooling is required, thermostat (TC1) closes, causing the
heat pump to start with an unloaded compressor. When TC2
closes, demanding additional cooling, the compressor loads
to full load operation.
During heating, compressor is always fully loaded. When TH1
demands first-stage heating, the heat pump starts within
3 seconds to 5 minutes depending on when unit was last
shut off by thermostat, because unit contains a Time Guard
circuit. (The defrost board has speed terminals to shorten this
cycle.) When TH2 of the thermostat closes, auxiliary heat sup-
ply (electric strip heat) is energized in 1 or 2 stages depend-
ing on number of stages available and whether outdoor ther-
mostats are closed.
Defrost is achieved by reversal from heating to cooling cycle
and deenergization of outdoor-fan motors, allowing hot re-
frigerant gas to defrost outdoor coil. Defrost is achieved with
a timer set to initiate defrost every 30, 50 or 90 minutes (fac-
tory set at 30 minutes).
Defrost is initiated when refrigerant temperature leaving the
outdoor coil is measured below 27 F, (typically when the out-
door ambient temperature is below 45 F as sensed by the de-
frost thermostat [DFT]).
Defrost is terminated when: The refrigerant temperature rises
to 65 F (80 F for 541A180) at the DFT location on the liquid
line; or the refrigerant pressure rises to 280 psig at the HPS2
location on the liquid line; or the defrost timer completes the
10-minute cycle.
Malfunction
The high-pressure switch, loss-of-charge switch, oil pressure
safety switch, and compressor overtemperature safety are lo-
cated in a Signal-LOC™ circuit that prevents heat pump op-
eration if these safety devices are activated. A light at the
thermostat energizes when Signal-LOC circuit is affected. The
lockout system can be reset by adjusting the thermostat to
open the contacts (down for Heating mode, up for Cooling mode),
deenergizing the Signal-LOC circuitry. Compressor overcur-
rent protection is achieved with a circuit breaker which re-
quires manual resetting at the outdoor unit control box.
The unit is equipped with an oil pressure safety switch that
protects the compressor if oil pressure does not develop on
start-up or is lost during operation. The oil pressure switch
is of the manual reset type and therefore must be reset at
the outdoor unit. DO NOT RESET MORE THAN ONCE.
If oil pressure switch trips, determine cause and correct. DO
NOT JUMPER OIL PRESSURE SAFETY SWITCH.
To reset the oil pressure switch:
1. Disconnect power to the unit.
2. Press the RESET button on the oil pressure switch.
3. Reconnect power to the unit.
Unit is equipped with a no-dump reversing valve circuit. When
unit is in Cooling mode, reversing valve remains in cooling
position until a call for heating is requested by thermostat.
When unit is in Heating mode, reversing valve remains in
heating position until there is a call for cooling.
The crankcase heater is in a lockout circuit. If crankcase heater
is defective, compressor is locked off. Heat pump remains off
until corrective action is taken. The lockout circuit cannot be
reactivated by adjusting the thermostat. To reset the crank-
case heater lockout, disconnect and then reconnect power to
unit.
C. Liquid Line Solenoid
To minimize refrigerant migration to the compressor during
the heat pump OFF cycle, the unit features a bi-flow liquid
line solenoid valve. The valve opens when the compressor is
energized, and closes when the compressor is deenergized. This
feature reduces compressor flooded starts, significantly in-
creasing compressor life.
D. Accumulator
The unit accumulator controls the rate of liquid refrigerant
to the compressor during heat pump operation. The accumu-
lator features a unique method for returning oil to the com-
pressor. The oil return mechanism is external to the accumu-
lator. The mixture of oil and refrigerant is metered to the
compressor by a brass orifice which is removable and clean-
able. The oil return mechanism also contains a solenoid valve
that opens when the compressor is ON and closes when the
compressor is OFF. This keeps the liquid refrigerant stored
in the accumulator from draining to the compressor during
the heat pump OFF cycle, which further protects the com-
pressor against flooded starts.
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