Blower Safety Switch Age?

[Michael Chambers]

Can anyone tell me about when they first started putting the safety cut-off switches into blower compartments? I ran into an old York today that could either be a 1972 or a 1993 model, but it appears to never have had that switch in it. There's not even a bracket for a switch. My money is on its being the older model, but I'd like to be sure. Thanks a lot for any help you can give me with this. :confused:

[Michael Chambers]

I ended up calling the manufacturer, and was told that they started putting the blower door safety switches in furnaces in the late 1980's. Hopefully this will help someone else as well.