I have a 22 year old Tempstar furnace model NUGG100EA02. The furnace works well. Recently I noticed that the cool-down cycle comes on a second time about 3 minutes after the main cool-down cycle. Is this acceptable normal operation or does the cool-down heat limiter switch need to be adjusted or replaced. Thanks!

It doesn't really hurt. It means that the off temp may be set too close to the on temp and it heat soaks the relay and kicks off again. Try moving the off temp down a bit or the on temp up a bit. Mine used to do that until I split the set points a bit more.

In case you do not know what the switch looks like here it is:http://www.plumbersstock.com/files/xref/large/55006.jpg You can see the sliding adjustments on the wheel. There are 3 of them: the one at bottom left is the fan off switch, next is the fan on switch, and the last one (at top) is the hi-limit and is non-adjustable.

Also check your furnace air filter. If it is restricted it could cause the same sort of problem and over heating. Short cycling can also occur. Furnace on and off more often than usual but shorter run cycles due to over heating.

Very good point because the sliding adjustments almost never need adjusting.