Auto Air Conditioning & Heater Repair: Heat thru Air vents, air vents, altima

Question
I have a 1998 Altima.  recently the check engine light came on.  I generally ignore these until I can get the dough for a mechanic.  Anyhow, a couple of days later I turned on the AC  and got warm air.  Additionally.. when I don't have any AC or heat on air comes through the vents.  Can you give me a clue? I may be able to reduce my hourly charge.

Thank you.

Answer
HI Maurice

On the altima if you push the button for the recirculating door you will stop having the air come in.  You check engine does not have anything to do with the ac.  Get some gauges on the system and let me know if you have pressure and what they are.