This may be a simple way to run a puller fan using only existing components..
As the high speed fan relay circuit is all there , it can be isolated
from the front fans by simply taking the fan feed wire from the relay to the low fan resistor off at the resistor common side and use this wire for puller feed .
You will no longer have the high aux fan, [ no longer needed]but will still have low fan for /ac pressure operation.
This point at the resistor is where the two circuits [high/low] come into common fan feed .[ fan is common to both circuits]
So , in reality , you now have the stock sensor [ which can be changed to any temp/spec using Jims chart w/metal-film parellel
resistor], and you have the K9 high fan relay/fuse circuit already
sitting there behind the the fuse box...wiring and all !!
nothing else needed ..
What da ya tink ????