1st time post, and new to diagnosing HVAC. Tho I'm pretty handy.
I have 2x Tempstar Heil NTxx series units (both about 15 yrs old) (dual zone home).
Both units are installed horizontally in the crawl space.
Natural Gas. System also has 2x AC compressors.
Up until now, both units have performed flawlessly.
On one of the units, I'm noticing the following behavior (note that this behavior does not happen consistently, often the unit works just fine).
(the fan setting on the thermostat is set to "AUTO")
Description of the problem (again not happening consistently).
1. The furnace kicks on, there is the expected delay, and then the blower comes on and everything works fine.
2. After about 6 or more cycles, the furnace will kick on normally, but the blower will never come on. And the furnace will keep running.
3. From the thermostat, if I turn off the unit for a period of time, and then back on, it seems to correct itself for awhile.
4. I am able to manually turn on and off the blower (fan) from the thermostat.
What could be causing the blower not to not consistently come on after the expected delay during a heating cycle
Thanks in advance for any ideas. I can provide more information if you let me know what would be needed.