Keeping AAF Herman Nelson Unit Ventilators Running: A Parts Guide for Schools
AAF Herman Nelson unit ventilators have been installed in schools and public buildings since the early twentieth century. Units built under the Herman Nelson, AAF, AAF-McQuay, and Snyder General names are still running, long after those companies merged, renamed, or ended support for the original products. Air Distributors has supplied parts for them since 1995.
Why parts are hard to find
General HVAC distributors stock parts for current equipment. Legacy unit ventilator parts, such as motors, bearings, damper actuators, couplings, coil assemblies, and controls for older configurations, are not on their shelves. Original documentation is often missing, and many part numbers have been superseded.
Common replacement parts
- Motors, matched to the original horsepower, voltage, frame, and rotation
- Bearings, including pillow block and shaft bearings, in the correct bore and load rating
- Couplings and drive components
- Coil assemblies
- Dampers and actuators that work with the existing control sequence
- Control components and boards for legacy configurations
We cover floor-mounted and ceiling-mounted units across several generations, including parts in the original critical parts lists issued under AAF, AAF-McQuay, and Daikin / McQuay.
Why the exact spec matters
A motor with the wrong frame or rotation may not mount or may run backward. A bearing with the wrong bore wears out fast. An actuator that does not match the control sequence can leave a damper open on a freezing night and take out a coil. Matching the original specification avoids those chain failures.
Identifying the part
- Get the unit's model and serial number from the nameplate.
- Note the part number on the failed component, if there is one.
- Photograph the part and how it mounts.
- For motors, record horsepower, voltage, frame, rotation, and RPM from the motor plate.
If the original part number is discontinued, we can often find the current equivalent from the model and serial number.
Plan for summer
Most districts have the most access to classrooms in summer. Order parts for known problem units in spring so they arrive before the work window.
See AAF Herman Nelson unit ventilator parts.
Send the model and serial number through the contact form or call 800-866-1210.