I had a similar problem with a relative's Rheem. Hooked up new Hunter 44272 tstat as "Single Stage Heat Pump w/ Aux Heat" = wrong. Works correctly as "Single Stage Heat Pump w/ Heat Reversing" For me, it was "B" and "O" wires.
Thanks. However the tstat is workiing and the compressor kicks on. The hot and cold lines act as normal. The fan does not click on automatically with comopressor. When I kick on the fan manually, the compressor shuts down. Have replaced the run capacitor for the fan but that was not the issue.