Bryant R-22 Thermistor Curve, Time Delays, Muffler, Accumulator, Reversing Valve RVS, Thermistors

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, 286A models there is a 1 minute time delay between staging from low to high and from high to low capacity. On 288A 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 286BNA and 288ANA, 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.

Muffler, Accumulator, Reversing Valve (RVS)

The Puronr two-stage air conditioners and heat pumps have a compressor discharge line muffler, to dampen sound pressure pulsations.

The Puronr two-stage heat pumps have a specifically designed reversing valve, for Puronr application and an accumulator for storing excess liquid refrigerant during the heating mode to prevent damaging flood-back.

Thermistors

Outdoor Ambient Thermistor

The Puronr two-speed air conditioner and heat pump units have an outdoor ambient air thermistor. The control board must know the outdoor air temperature so it can activate various functions. These functions include:

SActivating the compressor crankcase heater when ever the outdoor unit is in the off cycle.

SThe fan motor speed changes for both air conditioner and heat pump on the ECM equipped units.

Outdoor Coil Thermistor(OCT)

The coil or defrost thermistor is the same thermistor used to monitor outdoor air temperature. The control board must know the coil temperature so it can activate various functions. These functions include:

SFrost sensing on heat pumps

SCoil-vs-Ambient temperature relationship

SLow ambient cooling operation

Thermistor Curve

The resistance vs. temperature chart enables the service technicians to check thermistor resistance, regardless of the temperature.

For example, at a 60_F temperature, thermistor resistance should be around 16,000 Ohms. (See Fig. 34.)

We will talk about the thermistor in more detail when we review the control board fault codes.

THERMISTOR CURVE

	90
(KOHMS)	80
	70
	60
RESISTANCE	50
	20
	40
	30
	10
	0

0	20	40	60	80	100	120
(-17.77)	(-6.67)	(4.44)	(15.56)	(26.67)	(37.78)	(48.89)
		TEMPERATURE °F (°C)

A08054

Fig. 34 – Resistance Values Versus Temperature

49