your fans dont switch on at low speed when the A/C is started up?
you have an issue then. - pop open the fuse box and check all the fan relays. If you have an old model you should have 3 fan relays.
I have attached two generic toyota 3 relay fan system diagram and how they work
parallel (full speed)
series (low speed)
I think you may be able to understand how they are working.
If you have one single fan and the low speed is not functioning at all, then the above diagram is not valid.