with 20°F (11°K) superheat in the return gas.
High Pressure Control
A high-pressure cut-out is recommended for the
highest level of system reliability. If a high-pressure
cut-out control is used the maximum setting should not
exceed 650 psig (45 bar). The high-pressure cut-out
control should have a manual reset for the highest
level of system protection. It is not recommended to
use the compressor to test the high-pressure
switch function during the unit assembly line run
test.
Low Pressure Control
A low-pressure cut-out is recommended on all ZPS*KC
applications for the highest level of system reliability.
The low-pressure cutout should be set no lower than
20 psig (1.4 bar) for heat pumps and 55 psig (3.8 bar)
for air-conditioning units.
Discharge Temperature Protection
The ZPS*KC two-stage compressor does not have
Internal Pressure Relief valve.
Compressor top cap temperatures can be very hot.
Care must be taken to ensure that wiring or other
materials which could be damaged by these
temperatures do not come into contact with these
potentially hot areas.
All ZPS*KC two-stage compressors have Therm-O-
Disc™ temperature protection. The Therm-O-Disc™ or
TOD is a temperature-sensitive snap disc device
located between the high and low pressure side of the
scroll. It is designed to open and route excessively hot
discharge gas back to the internal motor overload
when the internal discharge gas exceeds 290°F
(144°C).
Crankcase Heat
A crankcase heater is required for systems containing
more than 120% of the compressor refrigerant charge
limit listed in Table 1. This includes long line length
systems where the extra charge will increase the
standard factory charge above the 120% limit.
Available crankcase heaters are listed in AE4-1365 or
Emerson.com/OPI. Refer to Figure 5 for proper
installation of the crankcase heater.
Crankcase heaters must be properly grounded.
Defrost Cycle
Defrosting with the compressor in full-load, versus
part-load, is highly recommended and will help defrost
the outdoor coil in a shorter period, reduce sound, and
help the reversing valve shift positions during low
outdoor ambient temperatures when flow conditions
can be low.
Reversing valve sizing must be within
the guidelines of the valve manufacturer. Required
pressure drop to ensure valve shifting must be
measured throughout the operating range of the
unit and compared to the valve manufacturer’s
data. Low ambient heating conditions with low flow
rates and low pressure drop across the valve can
result in a valve not shifting. This can result in a
condition where the compressor appears to be not
pumping (i.e. balanced pressures). It can also
result in elevated compressor sound levels.
Unloader Solenoid Wiring
The current in the ZPS*KC modulation solenoid
circuit must be less than 0.9 mA for the solenoid
valve to change from full-load to part-load. If
the current is greater than 0.9 mA the solenoid
valve can stay in full-load. A time delay relay or
another current consuming load in series with
the modulation solenoid could result in current
greater than 0.9 mA.
Standard Wiring with 24 Volts
A nominal 24-volt direct current coil activates the
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