Had a call from one of my tenants back this summer (Louisiana, humid, +100). AC had not cut off in 3 days and no air coming out the registers. I get there and check registers, no air flow. Positive pressure trying to come out of return. Filter was HORRIBLE!!! Wish I had a pic of that. Here is the 1 yr old 2 ton package unit. Copeland Scrolls are tough buggers! The only part not frozen was the top cap (muffler plate), the discharge was keeping it defrosted.
Pulled the covers and let it thaw for most of the day. Fresh filter and off it went. Now I personally PM the filters monthly to protect the coils. Tenants have NO PM SKILLS.