The outdoor copper tubes and compressor,accumulator,reverse valve get frosted. After you defrost it the unit cycles off and on with no problems for about 24 to 48 hours before it happens agian. I have not had to deal with Heat pumps to much.
check you air flo and filters. make sure all outlets are open. you may be low refrigerant but may not be. not all problems are refrigerant lose related. there may be a restriction in the system. call a service tech to help you out. heat pumps can get very diffacult and only someone that knows them should fix them
A priest, a minister and a rabbi walk into a bar. The bartender looks at them and says, Hey. Is this some kind of a joke?
Wait... sorry. You said no jokes.
Just to expand on the operator error theory: Setting it too low and/or running it at night doing the same will cause what you describe. I'm also inclined to think low airflow because of restricted ducts, a dirty filter or whatever. This isn't really any different than an AC problem.
The best answer given though was to call a real tech.
forget heat pump
lines and compressor freeze up i will assume the evap coil is also. now with 11 in the trade what will cause an ac unit to ise up. this is what you are dealing with when is the ac mode.
I'm betting dirty evap. coil. If it's a Trane, they have been having problems with check valves sticking of late also. Check the temperature on each side of each check valve. A valve that is open will have practicaly no temp difference side to side, a closed check valve will read different temps side to side. Figure out who is open and who is closed then check if that is the position it should be in at this time.
Post your superheat, subcooling temps. along with outdoor d.b., indoor w.b. temps, high and low side pressures, and if handy, your supply and return duct static pressure readings and I bet you will get answers from the professionals here.
There is nothing more frightful than ignorance in action....Mark Twain