This old post by Venerable Dhammanando might be helpful:
Re: Kamma and its Ripening in the Abhidhamma
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will: First she (Nina van gorkom)says "all cittas are beyond control" then "The cittas that like or dislike, and the cittas that think about the object, are not results but causes; they can motivate deeds which will bring fresh results." So I guess she means there are resultant cittas, all of which we have no control over and there are causal cittas which are causal because intention is there.
Actually intention (cetanā) is one of the universal mental factors (sabbacittasādhāraṇa cetasika), and so is present in every kind of citta, including vipākacittas. But the cetanā that arises with a vipākacitta is not kamma-producing; it merely performs the function of organizing its associated mental factors.
As for having control over it, bear in mind that intention is part of the fourth aggregate, formations. Concerning which the Buddha says:
"Bhikkhus, formations are not-self. Were formations self, then these formations would not tend to affliction, and one could have it of formations: 'Let my formations be thus, let my formations be otherwise.' But since formations are not-self, so they tend to affliction, and none can have it of formations: 'Let my formations be thus, let my formations be otherwise."
Will: Therefore over the causal cittas we do have control
Who is this "we" that has control?
"In all kinds of becoming, generation, destiny, station and abode, there appears only mentality-&-materiality (nāma-rūpa), which occurs by means of linking of cause with fruit. He sees no doer over and above the doing, no experiencer of the result over and above the occurrence of the result. But he sees clearly with right understanding that the wise say 'doer' when there is doing and 'experiencer' when there is experiencing simply as a mode of common usage.
"Hence the Ancients said:
There is no doer of a kamma
Or one who reaps the kamma's result;
Phenomena alone flow on—
No other view than this is right."
(Path of Purification, XIX 20)
In the Abhidhamma there's neither a controller of dhammas nor even one single dhamma that would be amenable to being controlled. Each conditioned dhamma arises, performs its function and falls away. There is no room here for an "I" or a "we".
- Will: how else would any transformation or purification occur?
In the Abhidhamma each stage and each aspect of purification, from going for refuge and undertaking the five precepts up to attaining the path and fruit of arahantship is explicated chiefly in terms of dhammas, not persons. How does it occur? Like everything else, it occurs by the arising of the necessary conditions for its occurrence. In particular:
The wholesome dhammas that constitute these stages of purification all have right view as their forerunner.
Right view arises in the present on account of past desire-to-act (chanda) and past volitions (cetanā) to engage in the actions that generate right view: consorting with the wise, hearing the Dhamma, discussing the Dhamma, and wisely reflecting on the Dhamma.
Right view will arise in the future on account of present desire-to-act and present volitions to engage in these actions.
Such volitions are generated through a combination of experiencing dukkha, encountering a faith-worthy object (the Triple Gem) and meritorious accumulations.