The low speed fan should run even if the aircon has no gas.
This might help:
https://www.the75andztclub.co.uk/for...ad.php?t=35567
The 2-speed fan system has the low speed resistor mounted on the fan guard. It's located in the 2 o'clock position behind the blades. You may have to turn the blades with a thin stick to get a clear view. In very rare cases, the resistor is reported to be out of sight to the rear RHS of the fan frame as you look at it.
TC