Rule 702.177b

An effect may allow you to take an action as long as you haven’t activated an exhaust ability this turn. Such an effect allows that action only if you haven’t begun to activate an exhaust ability this turn. Example: Elvish Refueler has an exhaust ability that costs mana and also has an ability that reads “During your turn, as long as you haven’t activated an exhaust ability this turn, you may activate exhaust abilities as though they haven’t been activated.” Loot, the Pathfinder has an exhaust ability that is also a mana ability. If you’ve already activated both of these abilities in a previous turn, you can’t activate Loot’s mana ability during the process of activating Elvish Refueler’s exhaust ability, because you have already begun to activate a different exhaust ability.