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System Operation
IMPORTANT
Some scroll compressor have internal vacuum protector
that will unload scrolls when suction pressure goes
below 20 psig. A hissing sound will be heard when the
compressor is running unloaded. Protector will reset
when low pressure in system is raised above 40 psig. DO
NOT REPLACE COMPRESSOR.
High Pressure Switch (S4)
This unit is equipped with a auto-reset high pressure
switch (single−pole, single−throw) which is located on the
liquid line. The switch shuts off the compressor when
discharge pressure rises above the factory setting. High
Pressure (auto reset) − trip at 590 psig, reset at 418 psig.
Low Pressure Switch (S87)
This unit is equipped an auto−reset low pressure switch
which is located on the vapor line. The switch shuts off the
compressor when the vapor pressure falls below the
factory setting. Low Pressure (auto reset) − trip at 25 psig,
reset at 40 psig.
Low Pressure Switch Bypass (S41) (Optional)
For use in applications where the heat pump is operated in
outdoor ambient temperatures below 15°F.
S
Prevents nuisance trips form the low pressure switch
S
Wired in parallel with the low pressure switch
Thermal Protection Switch (S173)
Mounted
Some units are equipped with a compressor mounted
normally closed temperature switch that prevents
compressor damage due to overheating caused by
internal friction. The switch is located on top of the
compressor casing (see figure 1). This switch senses the
compressor casing temperature and opens at 239−257°F
(115°C−125°C) to shut off compressor operation. The
auto−reset switch closes when the compressor casing
temperature falls to 151−187°F (66°C−86°C), and the
compressor is re−energized. This single−pole, single−throw
(SPST) bi−metallic switch is wired in series with the 24V Y
input signal to control compressor operation.
Crankcase Thermostat (S40) (−042, −048 and −060
Units Only)
The reference models are equipped with a 70 watt, belly
band type crankcase heater. HR1 prevents liquid from
accumulating in the compressor. HR1 is controlled by a
thermostat located on the liquid line. When liquid line
temperature drops below 50° F the thermostat closes
energizing HR1. The thermostat will open, de−energizing
HR1 once liquid line temperature reaches 70° F .
Defrost Thermostat (S6)
The defrost thermostat is located on the liquid line between
the check/expansion valve and the distributor. When
defrost thermostat senses 42°F (5.5°C) or cooler, the
thermostat contacts close and send a signal to the defrost
control to start the defrost timing. It also terminates defrost
when the liquid line warms up to 70°F (21°C).
506728−01
The unit is equipped with a large−capacity biflow filter drier
which keeps the system clean and dry. If replacement is
necessary, order another of the same design and capacity.
The replacement filter drier must be suitable for use with
HFC−410A refrigerant.
Defrost System
The XP13 defrost system includes two components: a
defrost thermostat (S6) and a defrost control (CMC1)
(figure 14).
LOW PRESSURE
HIGH PRESSURE
Compressor
DEFROST CONTROL (CMC1)
The defrost control includes the combined functions of a
time/temperature defrost control, defrost relay, diagnostic
LEDs and terminal strip for field wiring connections.
The defrost control provides automatic switching from
normal heating operation to defrost mode and back. When
the defrost thermostat is closed, the control accumulates
compressor run time at 30, 60 or 90 minute field adjustable
intervals. When the selected compressor run time interval
is reached, the defrost relay is energized and defrost
begins.
Each timing pin selection provides a different
accumulated compressor run time period for one defrost
cycle. This time period must occur before a defrost cycle
is initiated. The defrost interval can be adjusted to 30
(T1), 60 (T2), or 90 (T3) minutes (see figure 22). The
maximum defrost period is 14 minutes and cannot be
adjusted.
NOTE
timing pins.
S
S
If the timing selector jumper is missing, the defrost
control defaults to a 90−minute defrost interval.
Page 28
Bi−Flow Liquid Line Filter Drier
FIELD SELECT
TIMING PINS
TEST
PINS
COMPRESSOR
DELAY PINS
REVERSING
VALVE
S87
SWITCH
DEFROST
THERMOSTAT
S4
SWITCH
Figure 22. Defrost Control (CMC1)
Defrost Control Timing Pins (P1)
Defrost control part number is listed near the P1
Units with defrost control 100269−02: Factory default
is 60 minutes
Units with defrost control 100269−04: Factory default
is 90 minutes
DIAGNOSTIC
LEDS
24V TERMINAL
STRIP
CONNECTIONS
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