HVAC started intermittently swapping from A/C to heat on the driver's side?

I feel like a complete idiot for this and me and my dad are very mechanically inclined and have been working on vehicles for years. Years ago, the truck started intermittently swapping from A/C to heat on the driver's side on the 90–100-degree days of needing ac and that sucks working manual labor jobs and the vents still put off a little heat while the system is turned off. We have racked our brains for years messing with this thing. Here recently I started messing with it again because it is getting hot out. And neither side would work now and only put out heat. I ordered some of the $30 actuators off Amazon and I changed the driver and passenger side one and I was in business blowing ac that would run you out of the truck. And all of a sudden after about a month I would go around a turn or just be driving down the road and the driver side would just swap to heat. So, I ordered another $30 one and put it in a couple weeks ago and I think I got a 5-minute ride out of that one and then again back to heat on the driver's side. So, I was like I’m putting these cheap ass actuators in maybe that’s the problem. I then went to advance and theirs were only like $50 so I got one of those and put it in. I got maybe 20 minutes out of that one and it started blowing heat yet again. I’m starting to think it’s the climate control module that’s the problem but it’s kind of hard to go spend $200 on that part that may not fix the problem. And don’t have access to a scan tool to see if it’s throwing any codes. I really need help please because it’s getting hot out and I am starting to build a motor for the truck with it having almost 300000 miles on it and this truck has a lot of sentimental value to me so I want it to last another 20 years but I’m losing motivation in my build just for the simple fact of not being comfortable driving it because it’s so dang hot in the truck. It makes me just want to get rid of it. Any advice would help please and thank you.