My house has a Rheem heat pump, installed in 1991 Model
#RPND-042C, with "Heater Kit RXPJ," according to its
nameplate. Temperatures are about 35-40 degrees F this time
of year where I am.

Often in the morning the heat pump blows cold air for a
half-hour (or more?). I had an HVAC service tech out here a
week ago. He could not find anything wrong.

Does it simply take a while for the refrigerant to get to
suitable temperatures for evaporation/condensation operation
when in "heating" mode?

What symptoms might I observe that indicate the unit needs a
charge of refrigerant?

Also, I would like an operating manual, hopefully with a
layperson's troubleshooting guide. Although I am pretty
handy and I would prefer to do electrical side
troubleshooting myself. Anyone know where I can get such a
manual for this unit? I tried both the Rheem and Ruud sites;
no luck.