Bryant 551A Mechanical Cooling Lockout, Dry Bulb Changeover Set Up, Changeover Set Points

F. Mechanical Cooling Lockout

Determine the outdoor-air temperature at which you want the mechanical cooling (compressors) to be disabled. Locate the mechanical cooling lockout (MECH CLG LOCKOUT) potentiometer. To disable this feature, turn the potentiome- ter counterclockwise (CCW) to the OFF position. Otherwise, set the value between 10 and 60 F. Mechanical cooling will not operate when the outdoor air temperature is below this value. See Fig. 16.

G. Dry Bulb Changeover Set Up

Determine the dry bulb changeover set point from Table 6. The settings are A, B, C and D. Locate the ECON SP potenti- ometer and set the dry bulb changeover set point. See Fig. 16. When the OAT is above this set point, the damper is limited to minimum position setting.

If a potentiometer fails, its setting will default to the values in Table 7.

Table 5 — EconoMi$er Switchover Control Strategy

ECONOMI$ER SWITCHOVER STRATEGY		SENSORS REQUIRED
	Outdoor Air Temperature	Outdoor Air Enthalpy	Return Air Temperature	Return Air Enthalpy
Dry Bulb	X
Single Enthalpy		X
Differential Temperature	X		X
Differential Enthalpy*		X		X

*Must be selected manually.

Table 6 — Changeover Set Points

SETTINGS	A	B	C	D
Dry Bulb (°F)	73	69	66	63
Single Enthalpy* (Btu/lb)	27	25	24	22
Differential Temperature*	2	2	2	2
(°F, Not Adjustable)
Differential Enthalpy*	1	1	1	1
(Btu/lb, Not Adjustable)
*Field-installed accessory.

Table 7 — Default Potentiometer Settings

POTENTIOMETER	DEFAULT SETTING
CO2 SP (PPM)	1,000
MECH CLG LOCKOUT	50 F
ECON SP	D
MIN POS (%)	20

LEGEND

COM — Common

DAT — Discharge Air Thermistor

DM — Damper Motor

GND — Ground

OAH — Outdoor-Air Enthalpy Sensor

OAT — Outdoor-Air Temperature Sensor

POT — Potentiometer

RAH — Return-Air Enthalpy Sensor

RAT — Return-Air Temperature Sensor

REM — Remote

*OAT sensor shipped with economizer option. OAH, RAT, RAH and CO2 are field-installed accessories.

Fig. 23 — Typical EconoMi$er Wiring

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