car does not blow hot air when the heater is on and car is at operating temp.

INSTEAD OF THROWING PARTS AT IT WHY NOT LET THEM DIAG. IT COULD BE ALOT OF ISSUES WITH HVAC CONTROLS IN THE NEWER CARS.IT COULD SAVE YOU $ IN THE LONG RUN,ASK THEM IF THE WILL APPLY THE DIAG CHARGE TOWARDS THE REPAIR.

Unfortunately I too would agree, let the dealer diagnose the problem if they put in the wrong part and it doesn't fix the problem its their fault. If it is an electronic problem you would find it hard to diagnose for sure with out factory test instructions.