The Mars 50321 is a purpose-built 75VA step-down transformer that converts 120, 208, 240, or 480V primary power to a stable 24V secondary output -- the standard control voltage for residential and commercial HVAC, refrigeration, and heating systems. Low heat rise, NEMA Class II construction, and direct drop-in compatibility with a wide range of legacy transformers make it a reliable service replacement for technicians and serious DIYers alike.
Control circuits in air conditioners, heat pumps, furnaces, and refrigeration units rely on a consistent 24V signal to operate thermostats, contactors, and safety switches. When the transformer fails, the entire control circuit goes dark. The Mars 50321 restores that circuit quickly, with a multi-tap primary that covers 120V residential and 208/240/480V commercial applications from a single part.
Wire lead connections and a standard foot-mount footprint mean this transformer installs in the same space and with the same connections as the units it replaces. No bracket fabrication, no rewiring surprises -- just swap and restore.
Accepts 120, 208, 240, or 480V input -- one transformer covers residential and light commercial voltages without special ordering.
Delivers the industry-standard 24V control voltage required by most HVAC thermostats, contactors, and control boards.
Isolated secondary limits output current for inherent safety, meeting code requirements for HVAC control circuit applications.
Efficient core and winding design minimizes operating temperature, extending service life in enclosed equipment cabinets.
The Mars 50321 is a confirmed drop-in replacement for a broad list of discontinued and current-production transformers commonly found in field service situations:
Also sold and cataloged as NBK Parts 20606 -- same unit, same specs.
The integral foot mount matches the standard HVAC transformer footprint. Drop it onto the existing mounting surface, secure with the foot screws, connect the wire leads, and the installation is complete.
This transformer is suited for control circuit service in:
The 50321 is rated for both 50 Hz and 60 Hz power systems, making it suitable for North American 60 Hz installations as well as international or generator-sourced 50 Hz supply.
Primary leads are color-coded for multi-tap connection. Connect the lead matching your supply voltage (120, 208, 240, or 480V) to line, and leave unused primary taps insulated and capped. The 24V secondary leads connect directly to the existing control circuit wiring. Always de-energize the unit before installation and verify input voltage before energizing.
Before installing a replacement transformer, check the 24V control circuit for short-circuit faults. A shorted contactor coil or wiring fault will overload and destroy a new transformer immediately. Measure resistance on the secondary circuit before energizing.