The blower on my HVAC runs sometimes when it should be off. It does not run all of the time.
The furnace is in the attic and the abnormal running seems to be related to the attic temperature.
When the attic is not hot, all functions work properly, the blower is on when it should be on and off when it should be off.
With a hot attic (109 F), the blower was running with the thermostat in HEAT mode, fan in AUTO, and the set point 5 degrees below room temperature.
The blower continued to run when I switched the thermostat to OFF mode. The blower shut off overnight.
With a hot attic , the blower was running with the thermostat in COOL mode, fan in AUTO, and the set point 15 degrees above room temperature. The blower shut off overnight.
Is this normal behavior? If not, how do I determine what is causing the blower to run when it should be off?
Equipment - Installed 1981
General Electric natural gas furnace model BLH080E936G0
General Electric 5-wire thermostat model AY28X092 3AAT50A2B55I
Honeywell high limit and fan motor control L4064E 1223
Settings: high limit 205 F, Fan ON 120 F, Fan OFF 82 F