Air conditioner and furnace - mice!

[no268700]

I’m tackling all my mice issues this weekend prepping for my trip next week. I have a 2005 Shamrock 21SS. I think I have mouse nests in the hot air ducts (which look like dryer vent ducts). Can they be replaced? Do I have to use similar materials or is there something less chewable?
We haven’t used the air conditioner since we bought it a couple years ago (second owner). I’m not familiar with the units. One side has a slider to open it and it was stuck shut. Once I got it open there was a small nut that mice bring in. Is that where cold air blows out? Also, the white styrofoam that lines the ducts has broken down and falls out 2 of the vent holes. Any chance that it has aged and is crumbling or is it from mice?

[Daycruiser]

The foam has probably broken down on it's own. You may want to jerk the AC off the roof and inspect the whole installation at this point. 15years is a long time, there may be damage and age deterioration you can't see until you pull it apart.

[RiderBloke]

As all the ducts run in the ceiling and the ceiling should have no holes it is hard to imagine they came in that way. It may be possible they could get in through the roof unit and you could check that by removing the roof shroud and looking around. Check the input side and the output side are isolated from one another.
The larger screen with the two clips and the filter is the input side and the small grill with the open/shut slider is the output side and directs air out at the grill or through the ducting.
Check all the duct outlets too to make sure they are all securely in place.