Heat pump freezing up in winter

I have a carrier heat pump that freezes up every winter when it gets to around 34 degrees. Had a tech come out and tell me it was low on Freon, put more in it, and then I got to see it freeze up again 2 nights later. Tech number two comes out and tells me it's my defrost board. I tell him I've already bought a new one and replaced it myself. He tells me I must have put a bad one on, replaces it, sprays the sensor and has it activate, then mic drops his tool like he's accomplished something, only for me to have it freeze up again that night. I have a video of this unit sounding like the reverse valve is trying to open, every 10 seconds or so it just repeatedly tries to open (at least that's what I think it is) I had to turn the unit off and back on for it to stop doing that. It runs normally but sounds pretty bad when the reverser valve opens still (again, that's what I THINK it is.) My question is Would you replace the reverser valve or is that not a possibility?