Explosion Proof Packaged Cooling Unit, Split Unit

The multiplexor is a microprocessor-based programmable logic controller (PLC) 

control panel to manually or automatically control multiple Specific Systems units. 

Alternating control programs allow for automatic sequencing of multiple 

HVAC systems. When combined with the redundant refrigeration circuits 

standard with Specific Systems units, the multiplexer can greatly extend the 

life of the InPac’s compressors, fan motors and other components.

Several Form C alarm and indicator dry contacts are available with the 

multiplexors allowing easy installation into your existing remote monitoring 

system. The contacts include high/low temperature alarms and automatic 

activation of standby units or circuits as conditions warrant. The remote control 

panel shown at right is a custom alternating control panel for a dual InPac unit. 

Note that this panel incorporates additional controls for our purge & pressurization 

systems, variable speed fan motor drives, and redundant gas sensors/alarms 

If a failure of the main unit occurs (which can be determined through use 

of multiple sensors inside each HVAC unit), the multiplexer control automatically 

energizes a backup system to keep the area conditioned and provides visible 

local alarms to notify personnel of the failure. Remote alarms can be activated 

through the standard unit failure Form-C dry contacts. Energizing the backup unit 

can also be initiated by a power or other type failure of the lead unit or a high 

temperature alarm. All multiplexers include the ability to 

manually override or lockout any unit in the system.

With industrial wiring and components enclosed in a hinged 6" deep 

enclosure, Specific Systems’ multiplexers are built to withstand the same harsh

conditions as our InPac units. These panels are built in our UL listed electrical 

panel shop, labeled accordingly, and shipped ready for field installation.