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WSHP-PRC001-EN 15
Basic 24 Volt Controls
The basic 24 V electro-
mechanical unit control provides com-
ponent protection devices for maxi-
mum system reliability. Each device is
factory mounted, wired and tested.
See Figure 22 for the unit control box.
Safety Devices
System safety devices are provided
through the use of low/high pressure
switches in the refrigeration circuit to
help prevent compressor damage.
The switch and sensor are set to acti-
vate at refrigerant pressures of 20 psig
to fit most applications.
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 mechani-
cal communication of the low and high
pressure switches to prevent com-
pressor operation if the unit is under
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 23 for unit 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 small 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 24 for
24 volt stand-alone system controls.
Features and Benefits
Basic Controls
Figure 22: Basic 24 volt control box
Figure 23: Safety devices
Figure 24: 24 volt stand-alone system