Dude, that is some long term rust right there. That doesn't just happen. You have to have plenty of condensation for that.
 
My AC unit isn't hooked directly to the miners. It is simply just going into the fridge to try to sustain a consistent temp and prevent noise. The fridge isn't even running, I cut a freon line bc I was getting too impatient cutting the exhaust holes.

Aluminum/metal increases risk of condensation which is why I have eliminated all metal and only use PVC. I tested with aluminum dryer exhaust and that would condensate really bad.

I am running a dehumidifier that is collecting the condensation as much as possible.

I have 3 different Antminers in there and they are all running at 70 temps for over 6 months now. I have 3 fans in the fridge as well to help circulate the air which warms up the cool air slightly before entering the miner(hopefully).

All exhausted with PVC parts straight to the attic. I'm not seeing any condensation inside the fridge yet. Only on the outside of the fridge on the outside of the black PVC pipes going from the unit to the fridge. Because the temps are 100F+ here right now in the summer. No condensation on the inside of the pipes either.

It's working for now, will have to see long term what happens.

I think having a working fridge would increase condensation too but not sure of the outcome of this method vs just having a running fridge yet.