I was in Moab, UT three years ago Jeeping with friends. One day in the middle of nowhere we were sitting on some rocks having lunch when I noticed something round in the crevice of some rocks. I dug it out with a stick and it was a 1799 silver dollar in near perfect condition after mile...
I just shut it down for five minutes and then turned the thermostat up again. The blower kicked in only 18 seconds after the burners lit off. It must be a sensor that starts the blower instead of a timer.
The blower doesn't start at exactly the same number of seconds after gas ignition and that makes me think it is a sensor rather than simply a timed blower start. The model is HD 60AH0134
I have a 13 year old Modine Hawt Dog 60k BTU natural gas furnace heating the garage. If it sits for a few hours without running the heat exchanger warm up time before the blower comes on seems too long. The time can be a full 1 min 40 seconds and just about when the blower comes on the gas shuts...