Need to change out a Trane Baystat239 mercury thermostat. We purchased a Robertshaw 9620 replacement thermostat and would like to know if these are compatible before we get started. Also what if any concerns should we have when changing this model out because our system is so old (thermostat).

The 9620 Robertshaw is a 2 heat/2 cool tstat,, don`t no what kind of heat/cooling equipment you have .but it should work, I hope you have a manuel/install instruction sheet. Goodluck