Bryant R-22 Time Delays, Pressure Switches, Outdoor Fan Motor Operation, OutdoorFan Motor PWM

The outdoor Integral Control Motor (ECM), is a variable-speed motor which operates from 450 to 850 rpm. The motor is a dc permanent magnet-type motor with the electronic controls integrated into its rear cover. The control package includes a small diode bridge, capacitors, and power switching devices. It converts ac to dc power and switches the dc power to the motor windings on and off at various rates to control the motor speed. The speed at which the motor windings are thus commutated is determined by a pulse width modulated (PWM) signal which is received from the control board on the motor control lines.

The PWM signal is created by turning a DC signal on and off once within a given period of time. The signal on time relative to the signal total period defines the percent of the PWM. For example, if the period is 5 sec and the control power is turned on for 1 sec then off, the signal will remain off for 4 sec before turning on again to start the next cycle. The PWM is called a 20 percent duty cycle signal. If the on time is increased to 4 sec of the 5 sec period, the PWM is called an 80 percent duty cycle. The ECM reads the PWM signal and increases the motor speed linearly from minimum speed to maximum speed with the percent duty cycle value of the supplied PWM signal.

Outdoor Fan Motor Operation

There are two different types of motors used in the Evolution 2-stage outdoor units. The 286B models use a PSC type fan motor, and the speed does not change between high and low speed operation.

On 289B models, an ECM fan motor is used to achieve higher efficiency ratings of the system. 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. The 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/37.7°C. This reduces pressure differential for easier starting on next cycle. On 286B/187B models, the outdoor fan remains energized during the 1-minute compressor staging time delay.

On 286B/187B 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 289B/180B 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 19. The PWM output can be measured with a volt meter set to DC volts.

In low ambient cooling (below 55°F/12.7°C), the control board cycles the fan off and on.

Table 19—Outdoor Fan Motor PWM

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

		Low Stage		High Stage	Low & High
Model						Stage
	(OAT≤104_F / 40_C)			(OAT≤104_F / 40_C)
					(OAT>104_F / 40_C)
289BNA036		9.06		10.23		11.90
289BNA048		9.91		11.04		11.90
289BNA060		10.83		11.70		11.90
180BNA024		9.57		10.88		11.90
180BNA036		9.06		10.23		11.90
180BNA048		9.91		11.04		11.90
180BNA060		10.83		11.70		11.90
NOTE: For 289B models in low---			ambient cooling, the PWM output for
both high		--- and low---stage equals the value for low				---stage

operation below 55_F (12.8_C).

ECM Fan Motor Troubleshooting

If the outdoor fan motor fails to start and run:

SCheck the high-voltage supply. The unit need not be running to check high voltage, but the power must be on.

SIf the 230vac is present, use Table 19 to check for proper control voltage output to the fan motor from the control board. The control board sends DC voltage signals to the motor through the terminals labeled PWM1 and PWM2 Set a voltmeter on a DC voltage scale and check across these terminals.

SFirst check voltage with the motor disconnected. If no control voltage is present, check control-board connections. If connections are good, replace the control board.

SIf voltage is present, reconnect the motor and check again. Shut down the unit to reconnect the motor and restart the unit to complete this troubleshooting procedure. If control voltage is no longer present or motor fails to respond, check motor connections.

SIf connections are good, replace the motor.

Time Delays

The unit time delays include:

SFive minute time delay to start cooling or heating operation when there is a call from the thermostat or user interface. To bypass this feature, momentarily short and release Forced Defrost pins.

SFive minute compressor re-cycle delay on return from a brown-out condition.

STwo minute time delay to return to standby operation from last valid communication (with Evolution only).

SOne minute time delay of outdoor fan at termination of cooling mode when outdoor ambient is greater than or equal to 100_F.

SFifteen second delay at termination of defrost before the auxiliary heat (W1) is de-energized.

STwenty second delay at termination of defrost before the outdoor fan is energized.

SThirty second compressor delay when quiet shift enabled.

SOn 226A, 266A, 286B models there is a 1 minute time delay between staging from low to high and from high to low capacity. On 289B models there is no delay; the compressor will change from low to high and from high to low capacity “on the fly” to meet the demand.

Pressure Switches

The Puronr two-stage air conditioner contains two pressure switches to prevent system operation if the pressures get excessively high or low. The air conditioner low pressure switch in the suction line opens at 50 PSI and closes at 95 PSI. The high pressure switch opens at 670 PSI and closes at 470 PSI. Both pressure switch settings are considerably higher than on comparably sized R-22 units. The high and low pressure switches can be identified by their pink stripe on the switch’s electrical wires.

The Puronr two-stage heat pump contains a loss of charge switch in the suction line on 286B and 289B, and liquid line on 226A and 266A which opens at 23 PSI and closes at 55 PSI. See troubleshooting section for sequence when a pressure switch trip occurs.

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