Have a carrier weather master and am getting the error message that my rpm motor is out of range.. the heater works if I have it set in emergency mode..

Airflow restriction can produce this fault. Check air filter and, if possible, air conditioning coil (if present) for blockage.

What would change the fault by putting it to emg heat? I agree must be a airflow problem!

what would change the fault by putting it to emg heat? I agree must be a airflow problem!The emergency mode selection (DIP switch on circuit board) defaults the unit to maximum values for requested blower & inducer CFM/RPM . This is usually effective as a short-term solution when a secondary HX is restricted.