running thermostat control fan on, after hours of constant running it will shut down the fan and has trouble restarting or will not start at all until we switch to auto and back to on. Doing this constant run when using AC in summer.
How old is the unit and when was the last time it was serviced? What is the reason for running fan constantly if this is a residential system? You will need to check the following to isolate the problem: Proper voltage, amp draw on motor, proper airflow (cfm) in system, check motor air vents to see if they are clogged, check blower to see if the blades are clogged with dirt, check motor bearings, check that motor capacitor is within + - 10% of MFD rating and proper voltage rating.. Any one of these conditions will result in the motor overheating and or overloaded motor.