When do I apply the effect of Coolant Ammo when fired on a unit?
TacOps Advanced Units & Equipemt says on page 173
Coolant ammo also reduces the heat level for any heat-tracking target by 3 points (4 points when fired from a Heavy Flamer) per hit (to a maximum of 9 cooling points per turn).
It doesn't state when the effect is applied. If immediately, it would be able to influence to hit roles. If in the heat phase, it would not, but if the firing phase is handled correctly in order, could influence who an enemy inferno carrying unit is targeting.