I have a window unit air conditioner in my house. It has those little accordian pleated plastic pieces on each side that are supposed to fill in the gaps left in the window. They however do not , they left about a 1/4 in gap on one side underneath the plastic things and the window sill and about an inch on the other side. I loooked up last night and a rodent was coming in the space and a few minutes later crawled out the space. I stuck some plastic stuff in the gaps but I know they can chew though plastic pretty easy. I have been told that putting steel wool will deter them but that will rust in the humidity and rain etc. I had been planning on putting plastic over the area and taping it down so keep out the weather but keeping out the rats is a higher priority. What about aluminum foil? That would have the advantage of keeping out the light as well (I work second shift), I don’t think it rusts and I don’t think it would be considered food.
I have a window a/c unit, and this thread scares me. 
Aluminum foil might work, although I imagine it wouldn’t be that hard for them to chew through it, maybe even easier than plastic, depending on what you used; even if it was tightly pressed together, it would easily tear and separate into layers (and no, aluminum doesn’t rust, but if rats won’t chew it because it isn’t food, then they also wouldn’t chew plastic). It’d probably be best to put something solid, like pieces of wood, in the gaps, especially the 1 inch one, filling it as much as possible, maybe use plastic/foil to fill any remaining gaps (if rats are going to chew through wood, they might as well chew through your walls).
For some reason, I misread ‘keep out the weather’ as ‘keep out the weasel’. Have you considered not keeping out the weasel? He’d be very good at keeping rodents away.
If you’re not handy with tools, hire a carpenter to custom-build a baffle that fits the space and is permanently mounted. Or, if you remove the unit in the winter, semi-permanently mounted with screws that can be removed and reused. That will be better insulation than the thin plastic, anyway.
there is a product over here called space invader, you can probably get something similar, you spray it in and it expands like a marine foam to seal gaps.
If that’s anything like “Great Stuff,”[sup]*[/sup] it’s not intended to be exposed, but be a cavity filler in between more rigid components, and rodents can chew through it with ease.
- In spite of what the description says. Take it from experience, you don’t want it exposed to weather or house interior for long.
I appreciate the solutions offered. I realised afterwards that I didn’t really mean to say I didn’t know whether aluminum rusts but if it oxidises when exposed ie copper doesn’t rust but it does oxidise when exposed to weather for long periods a lovely green color that I don’t want all over my window sill.
With the weather we have in this area, the air conditioner stays in the window year round, I was running the ac last winter when we had some quite warm days. I have had 3 air conditioners in the 10+ years I have lived here and they are all different sizes so a permanant structure probably wouldn’t be the best idea. My boss at work suggested screening over the outside, so maybe that and aluminum foil covered piece of wood in the gap and then something on the inside to act as a further baffle against the weather and light.
i am also ordering some of the poison to put outside that is supposed to be only harmful to rodents and not to pets. I have no pets personally nor do any of my immediate neighbors but there are a couple of cats that roam the neighborhood (and like to sleep on my front porch for some reason) and while they don’t seem to be doing anything for the rodent population, I don’t wish them any harm.
maybe you could put some of that aluminium flashing type stuff around it
Reported for forum change, as annoying as rodents are.
We’ll send over a bottle or two of whiskey. You can take it from there.
a scrap of aluminum or steel flashing or siding would work.
cut each to the width of the space between the AC and window frame. cut each about 2 inches longer than the height of the opening on each side. bend 1 inch on the bottom and 1 inch on the top to make a very wide shallow U shape. slide in place from the outside.
I pit invading rodents!! (Sorry, forum change hasn’t happened yet.)
Rodents, especially rats, can chew through concrete. Neither aluminum foil nor plastic accordion pleats are rat proof. The question is, did this guy find anything inside (food, water, shelter) that could reward his foray? If so, he will likely attempt reentry. Depending upon the attractiveness of that reward, we may work pretty hard at it. If this is the case, your haphazard A/C mounting and repairs will be little inhibition.
You might just hope he found nothing worthwhile inside. Otherwise you will need to build or have built a secure, rigid frame of treated wood or metal or both.
Sorry for the bad news.
ETA: what **johnpost **said could work
Moved to IMHO.
I’m not sure why you won’t consider having a semi-permanent frame constructed. If your window units last an average of 3+ years, then it would be worth $50 or $100 to have a handy person come out and mouseproof this one.