Bryant 764A C. Unit Controls, D. Cooling Sequence of Operation, Ð Dry Coil Air Delivery Ð

C. Unit Controls

Compressor

High-Pressure Relief Valve Ð 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 Ð 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 air¯ow 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.

Air¯ow 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 Ð Dry Coil Air Delivery Ð

Horizontal Discharge

UNIT	IFM SPEED	AIRFLOW	ESP	POWER
564A/764A	SETTING	(Cfm)	(in. wg)	(Watts)
	Low	800	0.30	282
024	Med	800	0.65	349
	High	800	0.80	439
	Low*	1000	Ð	Ð
030	Med	1000	0.35	370
	High	1000	0.65	460
	Low	1200	0.30	445
036	Med	1200	0.50	480
	High	1200	0.65	530
	Low*	1400	Ð	Ð
042	Med	1400	0.30	495
	High	1400	0.60	571
	Low	1600	0.50	650
048²	Ð	Ð	Ð	Ð
	High	1600	0.65	720
	Low	2000	0.15	900
060	Med**	2000	0.60	850
	High	2000	0.65	945

LEGEND

ESP Ð External Static Pressure

IFM Ð Indoor (Evaporator) Fan Motor

*Unit is factory set on medium speed, this air¯ow is not obtainable at low speed.

²Size 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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