[windseeker]

FLS questions: (older Honeywell bimetal spring type - circular face with pin settings - limit off is fixed)
1) The Fan Off temp is varying by approx 10-12 degrees F which seems like a larger range than what I expected of maybe +/- 3 degrees. Comments? While not ideal, measuring the "Fan Off" temp variance at the register closest to the unit. Not specifically concerned with the actual Fan Off temp as much as the variation in temp when it shuts off, e.g sometimes shuts off when air at register is 70 F or 82F or anything in between. Of course variance concerns me also as to how it could relate to Fan ON or Limit Off settings.
2) The Limit Off setting is fixed at 150 F. Apparently common for this to be 200 F on natural gas systems. Is the lower setting related to the fact that this system burns propane?

System info: 16 year old American Standard (Trane) model # YCC036F1M0BA
Over the past couple years have personally replaced several items such as heat exchanger, motor capacitors, combustion blower, burners, turbulators, etc. Running on propane.

Thanks in advance for the assistance.

[EPMiller]

I wouldn't worry about that amount of shutoff temp difference at the register. As long if it is taking the heat off the furnace after it is done firing and purges the ducts down close to room temp you are fine. A bimetal coil will show some variation, especially if the pivot is a bit stiff from age.

Is the hi-temp limit shutting the burner down regularly? I can't believe your furnace works OK with that low a hi limit. Maybe you are looking at the fan cut-in setting. 150F would be more likely for that setting, although I think it may be on the high side. Can't remember. If the fan control is modulating the burner because of hi-limit cutout it should be adjusted or replaced.

I will let the experts here address the problem more fully, I only service one system that has this type of blower control, and as long as the system works fine, I don't worry much about it.

[KC13]

Why, thank you EP... :D The variance you are observing may be due to the control occasionally sticking at the end of a cycle. After 16 years, it may be wearing out. If the control has an auto/manual button, be sure it is fully out.