18 WSHP-PRC001-EN
Safety Devices
System safety devices are provided to
prevent compressor damage through
the use of low and high pressure
switches in the refrigeration circuit.
The low pressure switch or suction
line temperature sensor to prevent
compressor operation during low tem-
perature operation. The switch and
sensor are set to activate at refrigerant
pressures of 20 psig to fit most appli-
cations.
In cases where a low charge, or exces-
sive loss of charge occurs, each com-
pressor comes equipped with an
external overload device to halt the
compressor operation.
The high pressure switch prevents
compressor operation during high or
excessive discharge pressures that ex-
ceed 395 psig.
A lockout relay provides the me-
chanical communication of the low
and high pressure switches to prevent
compressor operation if the unit is un-
der low or high refrigerant circuit pres-
sure, or during a condensate overflow
condition. The lockout relay may be re-
set at the thermostat, or by cycling
power to the unit.
General alarm is accomplished
through the lockout relay and is used
in driving light emitting diodes. This
feature will drive dry contacts only,
and cannot be used to drive field in-
stalled control inputs.
See Figure 26 for safety devices on
the basic 24V control unit.
Stand-alone System
The 24 volt electro-mechanical design may be applied as a stand-alone control
system. The stand-alone design provides accurate temperature control directly
through a wall-mounted mercury bulb or electronic thermostat. This system
set-up may be utilized in a replacement design where a single unit retrofit is
needed. It may be easily interfaced with a field provided control system by way
of the factory installed 18-pole terminal strip.
This stand-alone control is frequently utilized on lower volume jobs where a
building controller may not be necessary, or where field installed direct digital
controls are specified. This type of control design does require a constant flow of
water to the water source heat pump. With a positive way to sense flow to the
unit, the units safety devices will trigger the unit off.
The stand-alone system design provides a low cost option of installation while
still allowing room control for each unit. See Figure 27 for 24 volt stand-alone
system controls.
Features and Benefits
Basic Controls
Figure 26: Safety devices
Figure 27: 24 volt stand-alone system
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