Before recharging system the air conditioner would blow cool and somtimes warm air and A/C lite would go out when it started to blow warm air. So I recharged the air conditioner on my nissan altima and it blew cold air while system was charging and after driving for 5 min. it started to blow warm air again. I did not see any spots were it could be leaking from and would the low line still have pressure if it were leaking? what are the possible problems?