The parts are on backorder. There is no indication of when they will ever arrive. They are only available from one company. This is the second central air system we've had in 12 years. They're fantastic when actually working. But they are ruinously expensive and almost impossible to fix when they break. And of course, these parts won't actually fix the damn machine, only make it possible to determine what else is broken, which might or might not be fixable and will probably take more months and months to repair.
I am left with the conclusion that the quality of both equipment and service in this industry is Russian-Monday, and the providers simply do not care if customers live or die.