What are the normal temperature settings for the fan limit switch on the a/c+gas heater blower unit?

The limit switch would be set about 180 degrees (this is the off temp.) The fan switch would be set to come on at 135 and go off at 100 to 105 degrees. This switch may have to be fine tuned to keep the fan from coming on during summer and to keep the fan from short cycling during normal operation.

keep the fan from short cycling during normal operation.
Is this the same as the fan coming on after the heat cycle has terminated? My Heil will fire up and blow air, but when the flame goes out the fan stops also. After 15-20 seconds the fan starts again and then may repeat 2-3 times. During this time the flame doesn't come on. Which limit is causing this activity?