Will covering the windows with thick painters plastic drastically help the window A/C unit cool the house down?Also, should i insulate the floor?
Aluminum foil over windows with direct sunlight will also help.
You don't want to do this, you'll screw up the minimal complete airflow needed to your AC to function and obviously freeze the unit up. This will go on to compressor failure and a as an alternative giant restore bill.
You can buy solar reflective film of amazon to stick to your windows to reflect some sunlight however this can be quite difficult to apply. If its humid trying buying a dehumidifier- takes the moisture out of the air which helps to make conditions more comfortable. Insulating the floor wouldn't be that beneficial as most, you want to reduce insulation in your loft and upper rooms! Hot air rises, so don't trap it!
Make sure the windows are closed (sometimes they slip from the top - be sure to check that). Using solar film will help but it is rough to work with, replace the screens with solar screening as it is easier and does help quite a bit. Insulating the floor will do very little, extra insulation in the attic is the way to go. Be sure to replace the AC filter as that could be clogged with dust. On very sunny days close the blinds or shades to help prevent heat build-up.
