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Welcome. My name is ***** ***** would be glad to assist.
Yes, swap those wires.
There is no way to know which wire they connected the fan to, except by checking the ceiling wiring
But based on what you have experienced, Swapping them should get you squared away.
Power connects to the one black on the switch, that will be the black wire in a different cable than the other black with red.
The cable with the black and red is the one to the ceiling.
Let me know any other difficulties,
Diagram is below in case