I had a customer that had another shop do a repair and what they did shocked me. There was multiple reason why this repair is not only dangerous but can lead to a fire. Never run Romex outside, never run a yellow Romex (20 amp) neutral to a white Romex (15 amp) neutral circuit, and always use a junction box to make AC connections. This video shows you what an open neutral looks like and how to diagnose. This works well for all AC circuits not just the air conditioner. Keystone didn’t have any documentation on this circuit in this guide and told me that there was no junction box for this AC circuit in between the breaker and air conditioner. This could be the answer to the issue in your Montana.