Bryant 542E - Manual (Page 13)

LEGEND
1B-Transformer
2A-lndoor Blower Relay SPST (N.O.)
2C-Outdoor Fan Relay SPOT
2D-Compressor Contactor DPST (N.O.)
2P-Defrost Relay TPDT
3D1-Outdoor Fan Motor
3D2-lndoor Blower Motor
3F-Compressor
3M-Defrost Timer
4A1-Fan Motor Capacitor
4A2-Blower Motor Capacitor
5B-Reversing Valve Solenoid
7K-Fan Switching Thermostat
SPOT
7M-Defrost Thermostat
Switch (N.O.)
7P-Low-Pressure Switch
SPST (N.O.)
11A-Crankcase Heater
When normally open defrost timer contacts between 3 and 4
close for their 10-second interval and defrost thermostat
switch 7M has switched close, the defrost control circuit is
completed and defrost relay coil 2P is energized.
Energized defrost relay coil 2P switches all of its contacts
and each of the following events occur simultaneously:
1. Normally open defrost relay contacts between 7 and 9
close before defrost timer 3M contacts between 3 and 4
complete their 10-second interval. The defrost control
circuit is maintained and defrost relay coil 2P remains
energized.
2. Normally closed defrost relay contacts between 7 amd 8
open and the circuit through outdoor fan motor 3D 1 is
broken. The motor stops running.
3. Normally open defrost relay contacts between 1 and 3
close, completing the circuit to reversing valve solenoid
5B. The reversing valve switches from the normal heat­
ing mode position to the cooling mode position and the
hot discharge gas is directed to the outdoor coil to melt
the frost on the coil.
4. Normally open defrost relay contacts between 4 and 6
close. Unit terminal R is now connected to unit terminal
W1 and the first bank of supplemental electric heat is
automatically energized. Terminals W1 and W2 of the
room thermostat are internally connected; therefore,
any additional banks of supplemental electric heat are
also automatically energized.
The system is now heating the conditioned space with the
supplemental heaters while the outdoor coil is defrosting.
When the outdoor coil refrigerant temperature rises to ap­
proximately 67°F, defrost thermostat 7M switches to the
open position to terminate the defrost cycle; however, if the
defrost thermostat 7M has not terminated the defrost cycle
within a 10-minute interval, normally closed timer 3M con­
tacts between 3 and 5 automatically open and terminate the
defrost cycle.
When the defrost cycle is terminated by either the defrost
thermostat or the timer contacts, defrost relay 2P is
deenergized. Outdoor fan motor 3D1 restarts and reversing
valve solenoid 5B is deenergized. The reversing valve
switches to the normal heating mode position. The supple­
mental electric heaters are deenergized if the room ther­
mostat is not “calling” for second-stage heating.
The system has now returned to normal heating mode opera­
tion. After 90 minutes of elapsed running time, defrost timer
3M will automatically make another check to determine if
the outdoor coil requires defrosting.
E. Emergency Heat Operation
When there is a heat pump compressor malfunction or other
malfunction in normal heat pump heating operation, it is
desirable to deactivate the compressor control circuit and to
remove the compressor from the heating system while con­
tinuing to supply the conditioned space with heat. Room
thermostats P/N 34427DP115 and P/N 34427DP118, which
have an emergency heat switch, are used to deactivate the
compressor and are used in conjunction with the accessory
supplemental electric heater to continue supplying heat. See
the Installation Instructions packaged with the electric
heaters for the emergency heat sequence of operation.
F. Automatic Changeover Operation
When autochangeover thermostat P/N 34427DP115 is being
used, the switching from heating to cooling to heating, is au­
tomatically controlled by the room thermostat when the
SYSTEM switch is in the AUTO position.
To prevent unwanted cycling between heating and cooling
mode operation, the heating and cooling temperature selec­
tion levers provide for a 4°F minimum temperature setting
differential. For most installations, this differential will
probably be set closer to 10°F to comply with recommended
guidelines for energy conservation.
With both the SYSTEM and FAN switches in the AUTO
position, the heat pump will start operation in the heating
mode when the room temperature drops to the thermostat
heating temperature setting, or will start operation in the
cooling mode when the room temperature rises to the ther­
mostat cooling temperature setting.
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