Granted Patent
Utility
US 4,171,621 · App. 05/478,530
Freeze protection device in heat pump system
Inventor:
Stephen W. Trelease
Patented Case
View Patent ↗
Granted: Oct 23, 1979
Filed: Jun 12, 1974
Inventor
Stephen W. Trelease
Assignee (at issue)
AMERICAN AIR FILTER COMPANY, INC.
This patent predates the USPTO's electronic file wrapper — prosecution documents from this era exist only in the Patent Office's paper records. A certified copy of the file history can be ordered from the USPTO's paper archives.