Residential HVAC (Heat Pump) question

Your best bet is let the tech look at it before you go any further.

The component you see through the top of the outdoor unit is the reversing valve. It is a slide valve and can get stuck in one position or the other. In some cases it can be tapped lightly to pop loose, but let the "pro" do that. (Edit: sometimes its not physically stuck...the solenoid could fail to trigger it for a couple of different electro-mechanical reasons).

The TXV is the component at the air handling unit that meters refrigerant into the coil. In heat mode it is bypassed outright.

You now know enough to be dangerous...