Take look the t stat in side if you see w1 and w2 then its a two stage t-shat. You need 5 wires for two stage setup.
red hot wire
white w1
green fan
yellow ac
blue could be w2 could be ground for t-stat
if its on w2 then its w2
if you have a wire on c then thats you common ground wire
or return wire to power up t-stat.
regards,
Kelvin