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Hi I'm Brian and I'm here to help!
It sounds like you might have an older furnace with a "Fan & Limit control" type of fan and safety control. Many of these are adjustable and they get out of adjustment over time. It's possible you can adjust it if that's the issue. A picture of yours would help, Click Here for a picture of a typical fan and limit control.
The actual model number of your furnace would be helpful too. The number you gave is for the ac a-coil that sits on top of your furnace. Your furnace's model number will likely be behind the blower panel you have to remove it to see it.