I have a 6341 that the ac cools but not enough air in cab to cool. I raised the top to get to the unit and cannot get to the reastat because the high speed does not work. After opening top the box housing the unit is all broken. I can get a new box for $600 but the problem is getting everything out of old box and all back in place. Should I replace the complete unit in the top of cab. any advise is welcome.