Our 17 year old, 2 ton Trane heat pump has gone belly up in the midst of a heat wave here in SC. We’re not desperate because this unit is used for our upstairs (about 1100 square feet) and our downstairs unit is pumping out cold air. We’ve had two contractors come out to give us estimates. Since we had a Trane, we thought we would go with another. The contractor that was here today recommended a Comfortmaker by Carrier and would not write a proposal for Trane (even though the company he works for carries it). His rationale was that the coils were now made of aluminum instead of industry-wide copper. I am familiar with how aluminum corrodes by thinking back to house aluminum wiring. So, first of all is this true on the Trane units and second of all, should I be concerned? I read this forum before calling contractors and expected the Manual J calculation to be done. Neither contractor did this, just based the size of the replacement unit on the overall square footage of the floor and the original unit and came up with another 2 ton unit. Maybe my third estimate will include that. The contractor this morning was concerned about the return duct and recommended an increase from 14 inch to 16 inch. I’ve noted this suggested improvement in the forum and wonder if this was common 15 years ago or is there a different formula being used now? I’ve gotten an education by reading this forum and hope others can weigh in on my above questions and learn more. Thanks

The thermostat in question is a 7 day programmable model. Its only a few years old. The problem is the room temperature is stuck on 74 when it is obviously lower then that. Should I ust replace the thermostat or is there something I am overlooking?