Bryant General Information, Evolution Controlled low ambient cooling, Defrost, 286B / 289B

286B / 289B

MODEL

PLUG

UTILITY RELAY *

UTILITY SIGNAL

OPEN RELAY

MODEL

PLUG

LLS

* SUPPLIED BY UTILITY PROVIDER	Liquid Line Solenoid
A06525	A06526

Fig. 6 - 2-Stage Control Board

GENERAL INFORMATION

Evolution Controlled low ambient cooling:

This unit is capable of low ambient cooling down to 0°F (-17.8°C) without a kit ONLY when using an Evolution Control. A low ambient kit is not required for Evolution controlled low ambient operation. The Evolution Control provides an automatic evaporator freeze thermostat. Low ambient cooling must be enabled in the User Interface setup. Fan may not begin to cycle until about 40°F (4.4°C) OAT. Fan will cycle based on coil and outdoor air temperature.

Evolution controlled low ambient mode operates as follows:

SFan is OFF when outdoor coil temperature is less than outdoor air

temperature (+ 3 _F/1.7_C) or outdoor fan has been ON for 30 minutes. (Fan is turned off to allow refrigerant system to stabilize.)

SFan is ON when outdoor coil temperature is less than outdoor air temperature (+25_F/13.9_C) or outdoor coil temperature is more than 80_F (26.7_C) or if outdoor fan has been OFF for 30 minutes.

(Fan is turned on to allow refrigerant system to stabilize.)

S Low pressure switch is ignored for first 3 minutes during low ambient start up. After 3 minutes, if LPS trips, then outdoor fan motor is turned off for 10 minutes, with the compressor running. If LPS closes within 10 minutes then cooling continues with the outdoor fan cycling per the coil temperature routine listed above for the remainder of the cooling cycle. If the LPS does not close within 10 minutes, then the normal LPS trip response (shut down cooling operation and generate LPS trip error) will occur.

Defrost

This control offers 5 possible defrost interval times: 30, 60, 90, 120 minutes, or AUTO.

Defrost intervals are selected by dip switches on the unit control board or by the Evolution Control User Interface. The Evolution Control selection overrides the control board dip switch settings.

Defrost interval times: 30, 60, 90, and 120 minutes or AUTO are selected by the Evolution Control User Interface (the dip switches are not used.)

AUTO defrost adjusts the defrost interval time based on the last defrost time as follows:

SWhen defrost time <3 minutes, the next defrost interval=120 minutes.

SWhen defrost time 3-5 minutes, the next defrost interval=90

minutes.

SWhen defrost time 5-7 minutes, the next defrost interval=60 minutes.

SWhen defrost time >7 minutes, the next defrost interval=30 minutes.

The control board accumulates compressor run time. As the accumulated run time approaches the selected defrost interval time, the control board monitors the coil temperature sensor for a defrost demand. If a defrost demand exists, a defrost cycle will be initiated at the end of the selected time interval. A defrost demand exists when the coil temperature is at or below 32_F (0_C) for 4 minutes during the interval.

The defrost cycle is terminated when the coil temperature reaches 65_F (18.33_C)or 10 minutes has passed. When OAT is > 25°F (-3.9°C), defrost will occur in low or high stage as demanded by the thermostat or User Interface.

If OAT is ≤25°F (3.9_C), defrost will occur in high stage only, regardless of thermostat or User Interface demand, and will terminate at 50_F (10_C) coil temperature with a minimum of 2.5 minutes in defrost.

If the coil temperature does not reach 32_F (0_C) within the interval, the interval timer will be reset and start over.

SUpon initial power up the first defrost interval is defaulted to 30 minutes. Remaining intervals are at selected times.

SDefrost is only allowed to occur below 50_F (10_C) outdoor ambient temperature.

The outdoor fan output (ODF) will remain off for 20 seconds after termination. This delay will allow time for the system to capture the heat from the outdoor coil and reduce the “steam cloud” effect that may occur on transition from defrost to heating cycle. The outdoor fan output OFF delay of 20 seconds may be defeated to enable the fan to energize immediately at the time of termination and 12 seconds prior to the reversing valve de-energizing through the User Interface setup screen (available with SYSTXBBUID01-C), or forced defrost pins as follows:

The ODF fan delay defeat can be toggled by shorting the forced defrost pins for >15 seconds while in the standby mode (status LED on solid). The LED will start to flash when the toggle has taken place.

8