Bryant 541A - Manual (Page 8)

E. Provide Safety Relief
A fusible plug is located on the compressor crankcase
(Fig. 8). Do not cap this plug. If local code requires additional
safety devices, install as directed.
Head Pressure Control
Fan cycling for head pressure control is a standard offering
but is functional on the cooling cycle only. Number 2 fan cycles
as a function of liquid pressure. Fan cycling pressure switch
cycles the fan off at 160 ± 10 psig as pressure decreases and
cycles back on at 255 ± 10 psig. Switch is automatically by-
passed in heating cycle. Table 6 shows minimum outdoor am-
bient air temperature for full cooling capacity.
Table 6 — Minimum Outdoor Air
Operating Temperature
UNIT
541A
%
COMPRESSOR
CAPACITY
OUTDOOR COIL
TEMP — F
MINIMUM
OUTDOOR
TEMP — F*
Standard Unit
120
100 90 35
67 80 45
180
100 90 23
67 80 36
*Applies to Cooling mode of operation only.
IV. STEP 4 — COMPLETE ELECTRICAL CONNECTIONS
A. Power Supply
Electrical characteristics of available power supply must agree
with nameplate rating. Supply voltage must be within toler-
ances shown in Table 7. Phase unbalance must not exceed
2%. Operation of unit on improper supply voltage or with ex-
cessive phase imbalance constitutes abuse and is not covered
by warranty.
Per local code requirements, provide an adequate fused dis-
connect switch within sight of unit and out of reach of chil-
dren. Provision for locking switch open (off) is advisable to
prevent power from being turned on while unit is being ser-
viced. The disconnect switch, fuses, and field wiring must com-
ply with local requirements. Refer to Table 7 for electrical
data. Route power wiring through entrance in right-hand cor-
ner post of unit. The power terminal block is sized to handle
either copper or aluminum wires. Unit must be grounded. Af-
fix crankcase heater warning sticker to unit disconnect switch.
B. Power Wiring
All power wiring must comply with applicable local require-
ments. Install a field-supplied branch circuit disconnect switch
that can be locked off or open. Run power wires from discon-
nect switch through unit power opening and connect to ter-
minal block inside the unit control box. See Fig. 9.
C. Unbalanced 3-Phase Supply Voltage
Never operate a motor where a phase imbalance in supply
voltage is greater than 2%. Use the following formula to de-
termine the percentage of voltage imbalance:
% Voltage Imbalance:
max voltage deviation from average voltage
= 100 x
average voltage
EXAMPLE: Supply voltage is 460-3-60.
AB = 452 v
BC = 464 v
AC = 455 v
452 + 464 + 455
Average Voltage =
3
= 457 v
Determine maximum deviation from average voltage:
(AB) 457 − 452 = 5 v
(BC) 464 − 457 = 7 v
(AC) 457 − 455 = 2 v
Maximum deviation is 7 v. Determine percentage of voltage
imbalance:
7
% Voltage Imbalance = 100 x
457
= 1.53%
This amount of phase imbalance is satisfactory as it is
below the maximum allowable of 2%.
IMPORTANT: Contact your local electric utility company
immediately if the supply voltage phase imbalance is more
than 2%.
WARNING: Unit cabinet must have an uninterrupted,
unbroken electrical ground to minimize the possibility
of personal injury if an electrical fault should occur. This
ground may consist of electrical wire connected to unit
ground lug in control compartment, or conduit ap-
proved for electrical ground when installed in accor-
dance with NEC (National Electrical Code), ANSI/
NFPA (American National Standards Institute/National
Fire Protection Association), and local electrical codes.
Failure to follow this warning could result in the
installer being liable for personal injury of others.
IMPORTANT: Operation of unit on improper power supply volt-
age or with excessive phase imbalance constitutes abuse and
is not covered by Bryant warranty.
D. General Wiring Notes
1. A crankcase heater is wired in the control circuit so it is
always operable as long as power supply disconnect is
on, even if any safety device is open or unit stop/start
switch is off.
2. The power-circuit field supply disconnect should never
be open except when unit is being serviced or is to
be down for a prolonged period. When operation is
resumed, crankcase heater should be energized for 24 hours
before start-up. If system is to be shut down for a pro-
longed period, it is recommended that the suction and
discharge valves be closed to prevent an excessive
accumulation of refrigerant in the compressor oil.
3. Terminals for field power supply are suitable for copper,
copper-clad aluminum, or aluminum conductors.
Fig. 8 — Location of Fusible Plug
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