The good news I've sorted my weak airflow from the heater blower ! It was a simple fix suggested by a mechanic friend and was, wait for it ! The plug on the motor was inserted the wrong way around, so the motor was blowing in the oppsite direction. Although the speed controller module has different sized terminals to prevent incorrect connection, the 2 pin plug on the motor can be inserted either way !!!!!! It was either like that from the factory or a previous owner inadvertantly plugged it in the wrong way. Initially I thought a blower motor going backwards would suck air, but no, it simply blows very inefficiently due to the design of the fan blades.
Mick