I've run into this with furnace blowers a lot. One nameless manufacturer produced hundreds of them in my area as heat pump system sections that were equipped with 1/2 HP motors instead of the proper 1/3 HP ones. We chased our tails for months, eventually changing the taps to the lowest speed so that they would at least run continuously.
Another contractor in the area finally figured out the issue and contacted the manufacturer's local rep. Fortunately, they provided replacement blower assemblies free of charge and paid us about $100.00 each to replace them.
Yes, the factory does make mistakes. Sometimes, they can be very costly ones.
