Bryant 764A - Manual (Page 13)

C. Unit Controls
Compressor
High-Pressure Relief Valve — Valve is located in compressor.
Relief valve opens at a pressure differential of approximately
450 psi between suction (low side) and discharge (high side)
to allow pressure equalization.
Internal Current and Temperature Sensing Overload —
Device resets automatically when internal compressor motor
temperature drops to a safe level. When an internal overload
is suspected of being open, check by using an ohmmeter or
continuity tester.
D. Cooling Sequence of Operation
NOTE: With the FAN switch in the ON position, 24 v is sup-
plied to the time-delay relay (TDR) through the G terminal
on the thermostat. This voltage energizes the coil of the re-
lay, closing the normally-open set of contacts which provide
continuous power to the indoor (evaporator) fan motor (IFM).
Moving the FAN switch back to the AUTO. position (provid-
ing there is not a call for cooling) deenergizes the TDR (when
applicable) which deenergizes the IFM after a 30-second de-
lay. The FAN switch in AUTO. position cycles upon a call for
cooling.
On a call for cooling, 24 v is supplied to the compressor con-
tactor (C) and TDR simultaneously through the Y and G ter-
minals of the thermostat, respectively. On units with a com-
pressor TDR, there is a built-in, 5-minute (±45 seconds) delay
between compressor starts. Energizing the contactor closes
the normally-open set of contacts supplying power to both the
compressor and outdoor (condenser) fan motor (OFM). Ener-
gizing the TDR closes the normally-open set of contacts pro-
viding power to the IFM. On the loss of the call for cooling,
24 v is removed from both the Y and G terminals of the ther-
mostat (providing the FAN switch is in the AUTO. position),
deenergizing both the compressor and TDR and opening both
the contacts supplying power to compressor and OFM. IFM
has a 30-second delay.
III. INDOOR AIRFLOW AND AIRFLOW ADJUSTMENTS
CAUTION: For cooling operation, the recommended
airflow is 350 to 450 cfm per each 12,000 Btuh of rated
cooling capacity.
Table 3 shows dry coil air delivery for horizontal discharge
units.
WARNING: Disconnect electrical power to the unit be-
fore changing blower speed. Electrical shock can cause
personal injury or death.
Airflow can be changed by changing the lead connections of
the blower motor.
Units 564A/764A024, 036, 048, and 060 blower motors are
factory wired for low speed operation. Units 564A/764A030
and 042 are factory wired for medium speed operation.
Table 3 — Dry Coil Air Delivery —
Horizontal Discharge
UNIT
564A/764A
IFM SPEED
SETTING
AIRFLOW
(Cfm)
ESP
(in. wg)
POWER
(Watts)
024
Low 800 0.30 282
Med 800 0.65 349
High 800 0.80 439
030
Low* 1000 — —
Med 1000 0.35 370
High 1000 0.65 460
036
Low 1200 0.30 445
Med 1200 0.50 480
High 1200 0.65 530
042
Low* 1400 — —
Med 1400 0.30 495
High 1400 0.60 571
048†
Low 1600 0.50 650
— — — —
High 1600 0.65 720
060
Low 2000 0.15 900
Med** 2000 0.60 850
High 2000 0.65 945
LEGEND
ESP — External Static Pressure
IFM
— Indoor (Evaporator) Fan Motor
*Unit is factory set on medium speed, this airflow is not obtainable at
low speed.
†Size 048 has low and high speed only.
**460 volt motors do not have a medium speed.
NOTE: Values for 208/230-v motors are at 230 v; deduct 10% for 208 v.
A. For 208/230-v Blower Motors:
The motor leads are color-coded as follows:
3-SPEED 2-SPEED
black = high speed black = high speed
blue = medium speed red = low speed
red = low speed
To change the speed of the blower motor, remove the fan mo-
tor speed leg lead from the indoor (evaporator) fan relay (IFR)
and replace with lead for desired blower motor speed. Insu-
late the removed lead to avoid contact with chassis parts.
B. For 460-v (2-Speed) Blower Motors:
The motor leads are color coded as follows:
black = high
yellow = jumper
purple = jumper
red = low
To change the speed of the blower motor from low speed to
high speed, remove the red lead from the indoor fan relay
(IFR). Insulate the red lead to avoid contact with any chassis
parts. Separate the black lead from the purple jumper. Con-
nect the black lead to the IFR. Insulate the purple lead to
avoid contact with any chassis parts.
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