Unitary Control for Residential HVAC
March 2006
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The UltraTech unitary control is for use in residential heat-pump and air-conditioning applications. The supplier says this is a first-of-its-kind control, combining several electromechanical controls with Emerson's Comfort Alert Diagnostics to provide what is said to be an unprecedented level of system reliability, ease of service, enhanced performance, and communication to the homeowner.

The unitary control incorporates a contactor, defrost control, two-speed compressor and fan control, and stand-alone short-cycle control with Comfort Alert Diagnostics onto a single circuit board with microprocessor (MCU) control. The MCU allows the outdoor unit to monitor its operation, display status and error codes and store fault history for service-technician retrieval. The Active Protection benefit of the diagnostics helps the homeowner avoid potentially damaging compressor operation by automatically shutting down the system for service and repair if a major system problem occurs.

The unitary control has several unique features, including the replacement of the contactor by a microprocessor-controlled, sealed relay. The relay has an embedded optical sensor to detect contact arcing and adjust the timing for opening the contacts, to provide near-zero cross-switching with minimal contact-point damage. Using a sealed relay also means that insects, such as fire ants, can't enter the unit and foul the contact points. Because the compressor and outdoor fan are switched by separate relays, "light flicker" can be reduced by effectively breaking up one large load into two smaller loads. The sealed switch features a manual-operation push button that can be used to run the compressor and fan for up to 5 minutes, thereby freeing the contractor's hands to do other work during system maintenance. Emerson Climate Technologies, www.gotoemerson.com

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