so a couple of things.
the a/c should be off a trinary switch. you would just need a signal, ground or positive to spin up the fan.
with the added delay.
what temp sensor are you tracking?

If there is no temp signal when the key comes on you go to 90 percent?

Have you tested this with the fan motor feets sent? just making sure it doesn't burn out at 90 percent for long period of time.
must supply over 30 amps to it.

and finally cost?