Bryant 286A Instruction Manual download pdf (Page 8)

One Minute Stage Change Time Delay on 286A Models

When compressor changes stages from high to low or low to high,

there is a 1--minute time delay before compressor restarts. The

outdoor fan motor remains running.

Compressor Operation on 286A Models

When the compressor operates in high stage operation, the

compressor motor rotates clockwise. Both the lower and upper

pistons are eccentric with the rotating crankshaft and both

compress refrigerant.

When the compressor operates in low stage operation, the

compressor motor reverses direction (rotates counterclockwise).

The lower piston becomes idle and the upper piston compresses

refrigerant. The start and run windings are reversed.

Crankcase Heater Operation

The crankcase heater is energized during unit off cycle regardless

of outside air temperature (OAT) on 286A models.

The crankcase heater is energized during off cycle below 65°F

(18.33°C) on 288A models.

Outdoor Fan Motor Operation

The outdoor unit control energizes outdoor fan anytime

compressor is operating, except for defrost or low-- ambient

cooling. The outdoor fan remains energized if a pressure switch or

compressor overload should open. Outdoor fan motor will

continue to operate for one minute after the compressor shuts off

when the outdoor ambient is greater than or equal to 100°F

(37.78°C). This reduces pressure dif ferential for easier starting on

next cycle. On 286A models, the outdoor fan remains energized

during the 1--minute compressor staging time delay.

On 286A models, the outdoor fan motor is a PSC type. A fan relay

on the control board turns the fan off and on by opening and

closing a high voltage circuit to the motor. It does not change

speeds between low and high stage operation.

On 288A models, the outdoor fan is an ECM type. The motor

control is continuously powered with high voltage. The motor

speed is determined by electrical pulses provided by the PWM

outputs on the control board. The ECM motor RPM adjusts to

outdoor conditions as described in Table 3. The PWM output can

be measured between the PWM1 and PWM2 terminals on the

circuit board with a volt meter set to DC volts.

In low ambient cooling (below 55_F/12.78_C) on 286A and 288A

models, the control board cycles the fan off and on.

Table 3 – Outdoor Fan Motor PWM

Outdoor Temp (DC volts, Tolerance +/-- 2%)

Model

Low Stage

(OAT≤104_F/40_ C)

High Stage

(OAT≤104_F/40_ C)

Low & High

Stage

(OAT>104_F/40_ C)

288A024 8.72 9.35 11.9

288A036 9.06 10.23 11.9

288A048 9.91 11.04 11.9

288A060 10.83 11.7 11.9

NOTE: For 288A models in low---ambient cooling, the PWM ou tput for

b o t h h i gh --- a n d l o w --- s t ag e e qu a l s t h e v a l u e f o r l o w --- s t ag e o pe r a ---

tion below 55_F (12.8_C).

Time Delays

The unit time delays include:

S Fiv e m in u te time d elay to start coo ling o r h eatin g o p eratio n

wh en th ere is a call fro m the thermo stat o r u ser interface. To

bypass this feature, momentarily short and release Forced

Defrost pins.

S Five minute compressor re-- cycle delay on return from a

brown-- out condition.

S Two minute time delay to return to standby operation from

last valid co m m u n icatio n (w ith Ev o lution o n ly ).

S One minute time delay of outdoor fan at termination of

cooling mode when outdoor ambient is greater than or equal

to 100_F (37.78_ C).

S Fifteen second delay at termination of defrost before the

auxiliary h eat (W 1 ) is d e-- en ergized.

S Twenty second delay at termination of defrost before the

outdoor fan is energized (unless fan delay defeated).

S Th irty seco n d co m p ressor delay w h en q u iet shift enabled.

S On 286A models there is a 1 minute time delay between

stagin g fro m low to high an d fro m hig h to lo w capacity. O n

288A models there is no delay; the compressor will change

from low to high and from high to low capacity “on the fly”

to m eet th e d em an d.

Compressor Operation on 288A Models:

The basic scroll design has been modified with the addition of an

internal unloading mechanism that opens a by--pass port in the first

compression pocket, effectively reducing the displacement of the

scroll. The opening and closing of the by -- pass port is controlled

by an internal electrically operated solenoid. The modulated scroll

uses a single step of unloading to go from full capacity to

approximately 67% capacity.

A single speed, high efficiency motor continues to run while the

scroll modulates between the two capacity steps. Modulation is

achieved by venting a portion of the gas in the first suction pocket

back to the low side of the compressor, thereby reducing the

effective displacement of the compressor.

Full capacity is achieved by blocking these vents, thus increasing

the displacement to 100%. A DC solenoid in the compressor

controlled by a rectified 24 volt AC signal in the external solenoid

plug moves the slider ring that covers and uncovers these vents.

The vent covers are arranged in such a manner that the compressor

operates at approximately 67% capacity when the solenoid is not

energized and 100% capacity when the solenoid is energized. The

loading and unloading of the two step scroll is done ”on the fly”

without shutting off the motor between steps.

NOTE: 67% compressor capacity translates to approximately

75% cooling or heating capacity at the indoor coil.

The compressor will always start unloaded and stay unloaded for

five seconds even when the thermostat is calling for high stage

capacity.

286A / 288A

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16

Comments to this Manuals

No comments

Bryant 286A Instruction Manual Page 8

Comments to this Manuals

Related products and manuals for Heat pumps Bryant 286A