How to mount an air conditioner in this window?
Based on your diagram, more or less what I have done. Jankiness level is variable depending on level of craftsmanship employed, or not.
The wood strip may need to be higher than the &quot;foam or wood&quot; strip as many air conditioners expect to find an edge to &quot;push&quot; against there. That's also why you might need screws to hold it in place (the A/C wants to rotate out at the top and in at the bottom. You want it to be held by those forces, not to give into them and fall.)