Hello ,
I'm trying to figure our why our AC works great for some time. Then it seems for no apparent reason starts blowing regular room temperature air instead of refrigerated air? After I shut it down for a while the process is repeated, cool for a while then the house starts warming up again. The furnace does not leak and I don't believe there is anything in the intake/outtake vents.
Please advise...

Well you have to tell us more than that. Next time it starts blowing warm air go outside and see if any thing is running. If nothing is running it is probably a defective contactor. It compressor is running (humming) but fan is not running, fan motor is probably failing due to capacitor failure. If fan is running but compressor is not running compressor may be failing to start due to faulty capacitor.
Of course the compressor may be in thermal over load because fan failed to start.