trap door for air on passenger side

[tds]

i'm slowly removing stuff i don't need or want in my truck like the rats nest of wiring and i slowly came across this trap door kinda set up on the passenger side firewall. what does it do? is it just a air return for the heater and ac? can i just get rid of it since i no longer have my ac and will be modifying my heat? seems to be a air return on fresh air make up. let me know if i'm wrong and your thoughts on removing it. thanks