Trane Model 180 GEV Basic Controls, Features and Benefits, Basic 24 Volt Controls, Safety Devices

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Features and Benefits

Basic Controls

Figure 20: Basic 24-volt control box.

Figure 21: BAsic 24-volt safety devices.

Figure 22: 24-volt stand-alone system.

Basic 24 Volt Controls

The basic 24 V electromechanical unit control provides component protection devices for maximum system reliability. Each device is factory mounted, wired and tested. See Figure 20 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 activate 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 exter- nal overload device to halt the com- pressor operation.

The high pressure switch prevents compressor operation during high or

excessive discharge pressures that exceed 395 psig.

A lockout relay provides the mechanical communication of the low and high pressure switches to prevent compres- sor operation if the unit is under low or high refrigerant circuit pressure, or dur- ing a condensate overflow condition. The lockout relay may be reset 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 installed control inputs. See Figure 21 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 con- trol system. The stand-alone design provides accurate temperature control directly through a wall-mounted mercu- ry 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 inter- faced with a field provided control sys- tem 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 con- trols 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 pro- vides a low cost option of installation while still allowing room control for each unit. See Figure 22 for 24 volt stand-alone system controls.

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