Good call on the big fan and the a/c. Check that your intake hole is LOW and LARGE- at LEAST 6" diameter, preferably a pair of holes, to make maximum usage of the blower you have.

Also avoid Hanna products like the defect-ridden plague they are, that can only read accurately when the solution has the ionic strength of fucking WASTE BRINE and even then aren't trustworthy! I wouldn't use one of those to test the water in my crapper, let alone my grow!