Might as well put in my two cents. First off you don’t have to have a VS motor for the two-speed equipment. All Carrier equipment with the exception of some builder grade stuff can operate a two-speed unit.
You do however require certain indoor equipment in order to use the Infinity thermostat. Your indoor equipment must be a 58CVA, 58MVP or the FE fan coil.
The outdoor sensor that comes with the TDB is wire tied in the condenser area. If it is not relocated to outside of the unit it will provide a high false reading.
The high false reading will force second stage latch at lower ambient temperatures. When left inside I find the sensor reads normal when the unit is not running. When the unit comes on the air being pulled across the condenser heats up the sensor by about 15 degree’s.
Example would be latch set at 90. Outside temp 75, unit comes on and sensor will heat up and read 90 degree’s forcing unit into high speed.
My advice is to be sure sensor is located outside the cabinet. Always check the simple stuff first!
Good luck
Live each day like it is your last, for one day you will be right!