AC/heater blower help needed

Hi. The heater blower on our 88 560sl is not working. The pneumatics are activating but nothing from the motor. I've replaced the fuse and have power across the
fuse. Somewhere I remember reading that the HVAC controls are temperamental and expensive to replace. How can I determine if it's the control or the blower motor malfunctioning. I've tried the archives at the site but the sl listings are not available. Any help is greatly appreciated.

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