Defrost Control; Quiet Shift; Defrost - Carrier 50JZ Installation, Start-Up And Service Instructions Manual

Speedup
Pins
with the lead for the desired blower motor speed. The motor speed
lead is attached to terminal BM. Insulate removed lead end to
avoid contact with chassis parts.
Step 3—Defrost Control

QUIET SHIFT

Quiet Shift is a field-selectable defrost mode, which will eliminate
occasional noise that could be heard at the start of defrost cycle
and restarting of heating cycle. It is selected by placing DIP switch
3 (on defrost board) in ON position.
When Quiet Shift switch is placed in ON position, and a defrost is
initiated, the following sequence of operation will occur. Revers-
ing valve will energize, outdoor fan will turn off, compressor will
turn off for 30 sec and then turn back on to complete defrost. At
the start of heating after conclusion of defrost reversing valve will
de-energize, compressor will turn off for another 30 sec, and the
outdoor fan will stay off for 40 sec, before starting in the Heating
mode.

DEFROST

The defrost control is a time/temperature control which includes a
field-selectable time period (DIP switch 1 and 2 on the board)
between defrost cycles of 30, 50 or 90 minutes (factory set at 30
minutes).
To initiate a forced defrost, two options are available depending on
the status of the defrost thermostat.
If defrost thermostat is closed, speedup pins (J1) must be shorted
by placing a flat head screw driver in between for 5 sec and
Quiet Defrost interval
Shift DIP switches
Fig. 23—Defrost Control
releasing, to observe a complete defrost cycle. When the Quiet
Shift switch is selected, compressor will be turned off for two 30
sec intervals during this complete defrost cycle, as explained
previously. When Quiet Shift switch is in factory default OFF
position, a normal and complete defrost cycle will be observed.
If defrost thermostat is in open position, and speedup pins are
shorted (with a flat head screw driver) for 5 sec and released, a
short defrost cycle will be observed (actual length is dependent
upon the selected Quiet Shift position). When Quiet Shift switch is
in ON position, the length of defrost is 1 minute (30 sec
compressor off period followed by 30 sec of defrost with com-
pressor operation). On return to heating operation, compressor will
again turn off for an additional 30 sec and the outdoor fan for 40
sec. When the Quiet Shift is in OFF position, only a brief 30 sec
cycle will be observed.
If it is desirable to observe a complete defrost in warmer weather,
the defrost thermostat must be closed as follows.
NOTE: Unit will remain in defrost until defrost thermostat
reopens at approximately 80°F (26.7°C) coil temperature at liquid
21
CESO130076–00
1. Turn off power to outdoor unit and install lockout tag.
2. Disconnect outdoor fan motor lead from OF2 on control
board. (See Fig. 19) Tape to prevent grounding.
3. Restart unit in Heating mode, allowing frost to accumulate on
outdoor coil.
4. After a few minutes in Heating mode, liquid line temperature
should drop below closing point of defrost thermostat (ap-
proximately 30°F /-1.1°C).
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