Heat Pumps and Electric Heating - Rheem Heat pump Blower

I have a Rheem Heat Pump. The system operates fine in the Air Condition mode, but in Heat mode, the inside Air Handler blower does not shut off.

When the temp is reached on tstat, the heat pump shuts off, but the blower continues to run. I have changed the Tstat and all wires with no luck on solving the problem.

When heat pump turns off, the only voltage from tstat is on the red wire.

The inside Air handler is new, however the old unit had the same problem.

I wonder if the defrost board could be the problem?

Any help would be greatly appreciated.

Did you install a new t-stat with the air handler? Anyway next time the blower fails to stop pull the green wire off the air handler terminal. If it stops then replace or reprogram the t-stat (if it is reprogrammable) If it continues to run then you may have a defrost control problem.

Yes, I tried two tstats.

When the heat pump cycles off, there is not any votage going to the green wire.

Is the fan timed to continue to run for a period of time after the heat pump shuts down? The reason I ask is the tstat is directly above the return. I am wondering if the return starts pulling cold air and the temp drops a degree or so before the cycle is complete.