i've been fighting with a mr slim model pla42aa ceiling casette system for the past three weeks. originally i had a p4 code which was a bad condensate lift pump (the thing was cooking). replaced that and then wound up replacing the drain sensor today, which is where i still am. now my wired controller is giving me a U4 error code?????? anyone know what this means. mitsubishi tech support is horrible when it comes to speedy response time and i'm just sitting here twiddling my thumbs.