TWO SPEED

FAN

TWO SPEED

THERMOSTAT

COIL

HEAT PUMP

 

 

 

 

 

 

W2

 

W2

 

 

W2

 

 

 

 

 

 

 

 

 

CONTROL

 

 

W3

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

LOGIC

 

 

 

 

 

 

 

 

 

 

 

 

 

W3

 

 

 

 

 

 

 

 

 

 

A93572

PRESSURE SWITCH PROTECTION

The outdoor unit is equipped with high- and low-pressure switches, wired in series. If a pressure switch opens, the control provides a 5-minute time delay in outdoor unit operation with the outdoor fan running. A malfunction signal appears on the control when a pressure switch opens. If the switch remains open for 1 hr or longer, a malfunction signal is provided at the L terminal of the indoor thermostat.

Fig. 36—Low-Voltage Control Wiring

AUXILIARY HEAT (W2) LOCKOUT

In some areas, it is necessary to disable the auxiliary heat, except for defrost, until the outdoor ambient is less than the structure’s balance point. This is accomplished by using the low-voltage wiring as shown in Fig. 36. Wire the 24vac W2 signal from the indoor thermostat to W3 of the control, and W2 of the control to W2 of the indoor unit. When the outdoor ambient is less than the setting of the balance-point POT, the 24vac signal energizes the auxiliary heat (W2) of the indoor unit.

EMERGENCY HEAT

If the 2-speed control receives a call for auxiliary heat (W2) without a heat-pump heating (Y1) call, the second auxiliary stage (W3) is energized. This ensures all available heat is energized if the indoor thermostat is switched to emergency heat.

COMPRESSOR PTC-OVERLOAD PROTECTION

The control senses the resistance of the compressor internal positive-temperature coefficient (PTC) overloads. If the resistance of the PTCs is out of range, the control shuts off the unit until the resistance range is acceptable. See Table 16 for compressor PTC ranges.

TABLE 16—COMPRESSOR PTC RANGES

COMPRESSOR INTERNAL-PTC RESISTANCE

Safe Range (77°F)

1.5k to 7.8k ohms

To trip

26k to 34k ohms

To reset

8.4k to 10k ohms

When the control turns off the outdoor unit due to out-of-range PTCs, the unit remains off for 15 minutes with the outdoor fan running. After 15 minutes, the control checks the resistance every 5 minutes until it reaches the reset range. During this time, a malfunction signal appears on the control board. If this happens, remove the wires on control board at S1 and S2 and measure the resistance across the leads. When the resistance reaches 8,400 to 10,000 ohms, system operation may be resumed. If the resistance remains outside this range, a quick check of the leads at the compressor should be made. Loose connections can cause inaccu- rate readings. If a PTC trip occurs 3 times, the control will lock out the outdoor-unit operation and provide malfunction signals at both the control and indoor thermostat.

III. FACTORY DEFAULTS

Factory defaults have been provided in the event of failure of the ambient thermistor, outdoor-coil thermistor, and/or furnace inter- face jumper. Refer to Table 17 for default and function.

IV. MAJOR COMPONENTS

TWO-SPEED CONTROL

The 2-speed control board controls the following functions:

•High- and low-compressor contactor operation

•Outdoor fan-motor operation

•Crankcase-heater operation

•Compressor protection

•Pressure-switch monitoring

•Second-stage latching

•Time delays

•5-minute time-delay speedup (bypass)

Heat pumps:

•Time/temperature defrost

•Defrost-interval selection

•Furnace interface

•Electric-heat staging

HEADER-PIN HOUSING

The header-pin housing is the plastic assembly which holds the stripped-lead ends for field connections. The 2-speed control receives the 24vac low-voltage control-system inputs through the housing/pins. The housing also contains jumpers which the control uses for system configuration, such as heat pump versus air conditioner. See Fig. 37 for header-pin housing configurations.

TWO-SPEED COMPRESSOR

The 2-speed compressor contains motor windings that provide low-speed, 4–pole (1750 rpm) and high-speed, 2–pole (3500 rpm) operation. Refer to Fig. 38 to determine which windings are energized at each speed. Refer to Compressor Winding-Check section under Troubleshooting and Table 18 for appropriate winding resistances.

The 2-speed compressor is also protected by an internal-pressure relief (IPR), which relieves discharge gas into the compressor shell (low side) when the differential between suction and discharge

TABLE 17—FACTORY DEFAULTS

FAILED COMPONENT

FUNCTION

DEFAULT

 

Crankcase Heater

Energized during any off cycle

 

 

 

 

Second-Stage Latching

Does not function

 

 

 

 

 

Balance point does not function, but

 

Furnace Interface

interface still energizes furnace and

 

 

locks out heat pump with a call for W2

Ambient Thermistor

Heating Switchover Speed Point

Unit only runs in high-

 

compressor speed

 

 

 

Defrost Initiation

Defrost is initiated based on coil

 

temperature only

 

 

 

Outdoor Thermostat for

Anytime there is a call for W2,

 

Auxiliary Heat

W3 is also energized.

Outdoor Coil Thermistor

Defrost Initiation and Termination

Defrost occurs at each time interval,

but terminates after 5 minutes

 

 

Furnace Interface Jumper

Furnace Interface

Does not function

 

 

 

—33—

Page 32 Page 34
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Bryant R-22 service manual Compressor PTC Ranges, III. Factory Defaults, IV. Major Components
Page 32 Page 34

R-22 specifications

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