Went on a call at a church, and was told "it's just not cooling". They said "it just stopped. Nothing's coming out of the vents". Turned out to be a broken belt that cut some of the wiring to the blower motor when it broke, but it couldn't have been cooling well prior to the belt breaking. Not with filters like this:
This coil was on the third cleaning when I could finally see the fins. This was on a 7.5T package unit, cooling only. After I got it cleaned up and running well, the unit was most grateful, and cried all over the sidewalk working to rid the sanctuary of all of that heat load!!
I had to ask, "When was the last time someone came to service this unit?" They stated, "According to the box of filters, someone was here 5 years ago, but it was working fine till now." Ahhhhhh!