OK here is the deal,

This is a small 2000 sf machine shop. This place gets hot so we bought a 28,000 Btu air conditioner to knock out a little heat and humidity ( I know its not enough but every bit counts. Instead of cutting a big hole in the cinder block (we are renting this place) I decided to build a room around our air compressor ( It creates a lot of noise and heat ) with a fan blowing in from the bottom ( shown in pics ) and a fan blowing out at the top. I then mounting the a/c unit into the room so it would expell the hot air into the vented room.

It has worked great to quite the compressor and remove the heat but the a/c unit is acting up. when I first turn it on, it blows nice cold air, after about 5 or ten minutes it blows room temp air. is it possible I don't have enough ventilation? Looking for some answers and thanx for all help