I have a unit that I cannot find an issue with. Pressures are good, coils are clean but the unit fails over night. Belt was super tight and had black dust on the pully so I changed the belt and check the bearings. Everthing looks good. The tstat keeps reading cool fail when I return but I can never find a problem and the unit runs great all day. Been going on for a few days. Can anyone take a stab at this.