What are the needed procedures to follow in changing air filters on Carrier 4.5 KG roof top mounted model 48HJD005---551--unit. I understand they use 2 16x25x2 inch filters. Access is clearly pointed out on the outside of the unit, but what pecautions are needed, what advise do you recommend for a first time installer? Thanking you in advance! My e mail is [email protected]