I have a Rheem model no. RHQA 1000B heat pump, but previous homeowner left no manual for it. I am puzzled at the "EM" setting on the thermostat. I would also like to download/obtain an operation manual for this unit.

EM usually means emergency heat. All it does is bring on the strait electric heat in the furnace. It is more expensive to heat that way than it is to use the heat pump.