How to fix this hole?

[Roland]

If your A/C works; if your heater core doesn't leak, I'd steer clear of removing the case half. You will probably have to remove the entire unit in order to get this side off but if you are able to remove the one side, you will ruin the seal and have to take the other side off to replace it anyway. If you are going to add a vacuum canister, it could be used to cover any repair you make to the hole and if you only want to stop up the hole why not go to an electrical supply house (or maybe even Home Depot) and get a conduit plug which is used to plug unused holes in electrical boxes. Another alternative would be a plug used by plumbers to stop up unused holes in a kitchen sink. If you are insistent on removing the side, I think I have an extra one that has no breaks. I will have to look. If you need it let me know.