Bryant LEGACY 213R Service Manual download pdf (Page 16)

FEEDER TUBE

DEFROST

THERMOSTAT

STUB TUBE

A97517

Fig. 9 – Defrost Thermostat Location

Defrost Thermostats

Defrost thermostat signals heat pump that conditions are right for

defrost or that conditions have changed to terminate defrost. It is a

thermally actuated switch clamped to outdoor coil to sense its

temperature. Normal temperature range is closed at 30_ ± 3_Fand

open at 65_ ± 5_F. Defrost thermostats are used in Legacy RNC

and Legacy Line models, a coil temperature thermistor is used in

Preferred and Evolution units.

Check Defrost Thermostat

There is a liquid header with a brass distributor and feeder tube

going into outdoor coil. At the end of 1 of the feeder tubes, there is

a 3/8-- in. OD stub tube approximately 3 in. long. (See Fig. 9.) The

defrost thermostat should be located on stub tube. Note that there is

only 1 stub tube used with a liquid header, and on most units it is

the bottom circuit.

NOTE: The defrost thermostat must be located on the liquid side

of the outdoor coil on the bottom circuit and as close to the coil as

possible.

Defrost Control Board

Troubleshooting defrost control involves a series of simple steps

that indicate whether or not board is defective.

NOTE: This procedure allows the service technician to check

control board and defrost thermostat for defects. First, troubleshoot

to make sure unit operates properly in heating and cooling modes.

This ensures operational problems are not attributed to the defrost

control board.

HK32EA001 Defrost

Control

The HK32EA001 defrost control is used in all Legacy RNC heat

pump models 213A, 214A and 213R. Its features include

selectable defrost intervals of 30, 60, 90 minutes, and standard

defrost speed up capability. This section describes the sequence of

operation and trouble shooting methods for this control.

Cooling Sequence of

Operation

On a call for cooling, thermostat makes R--O, R--Y, and R-- G.

Circuit R--O energizes reversing valve switching it to cooling

position. Circuit R-- Y sends low voltage through the safeties and

energizes the contactor, which starts the compressor and ener gizes

the T1 terminal on the circuit board. This will energize the OF2 fan

relay which starts the outdoor fan motor.

When the cycle is complete, R-- Y is turned off and compressor and

outdoor fan should stop. With Bryant thermostats, the O terminal

remains energized in the cooling mode. If the mode is switched to

heat or Off, the valve is de--energized. There is no compressor

delay built into this control.

Heating Sequence of

Operation

On a call for heating, thermostat makes R--Y, and R--G. Circuit

R-- Y sends low voltage through the safeties and energizes the

contactor, which starts the compressor and energizes the T1

terminal on the circuit board. The T1 terminal energizes the defrost

logic. This will energize the OF2 fan relay start the outdoor motor.

The T1 terminal must be energized for defrost to function.

When the cycle is complete, R--Y is turned off and the compressor

and outdoor fan should stop. There is no compressor d elay built

into this control.

Defrost Sequence

(HK32EA001)

The defrost control is a time/temperature control that has field

selectable settings of 30, 60, and 90 minutes. These represent the

amount of time that must pass after closure of the defrost

thermostat before the defrost sequence begins.

The defrost thermostat senses coil temperature throughout the

heating cycle. When the coil temperature reaches the defrost

thermostat setting of approximately 32ºF, it will close, which

energizes the DFT terminal and begins the defrost timing sequence.

When the DTF has been energized for the selected time, the defrost

cycle begins, and the control shifts the reversing valve into cooling

position, and turns the outdoor fan off. This shifts hot gas flow into

the outdoor coil which melts the frost from the coil. The defrost

cycle is terminated when defrost thermostat opens at approximately

65ºF, or automatically after 10 minutes.

OUTDOOR FAN

RELAY

Y OUTPUT TO PRESSURE

SWITCHES AND CONTACTOR

THERMOSTAT INPUTS

T1 - ENABLES DEFROST

TIMER. MUST BE

ENERGIZED FOR

DEFROST TIMER

TO START

C - COMMON

O - REVERSING VALVE

SPEEDUP

HK32EA001

DEFROST THERMOSTAT

MUST BE CLOSED BEFORE

DEFROST TIMER BEGINS

A05332

Fig. 10 – HK32EA001 Defrost Control

1 2 ... 11 12 13 14 15 16 17 18 19 20 21 ... 65 66

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Bryant LEGACY 213R Service Manual Page 16

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