Heat pump blower motor cycles on/off after running 140 seconds

Sounds like your defrost cycle isn't kicking in. There is a defrost circuit in most newer units that controls that cycle, in which the unit runs in reverse -- literally taking heat from your house to defrost the unit. I'd turn it off ASAP if that's the case since it's just wasting electricity and call a tech to have a look and possibly replace the circuit board. Tell them what's going on ahead of time and maybe they will have the part with them when they come out!

If the outdoor fan comes on and the compressor does not, you need a "hard start kit" this is either a potential relay and start capacitor as in my diagram or a PTC thermistor solid state start assist device that piggy backs onto the run capacitor. This is assuming your compressor is cold to the touch and has not been starting. If your compressor has been starting and is off due to the thermal overload being open Then it is due to the capacitor being bad or refrigerant being low or the compressor is mechanically tight or electrically shorted to itself internally, this is not something a homeowner will usually be able to do unless walked through it step by step.