Let $A$ be an abelian category that has a generator and satisfies the AB4 axiom. I would like to understand (better) the relations between various additional "restrictions" on $A$.


So here is my list of additional "axioms":


(1) $A$ is an AB5 category (and so, Grothendieck abelian).


(2) There is an exact conservative functor from $A$ into abelian groups that respects coproducts (and so, colimits).


(3) $A$ has an injective cogenerator, satisfies the AB3\* axiom, and sending an object of $A$ into the functor it corepresents on the category $Inj A$ (of injective objects of $A$) gives an equivalence of $A$ with the category of those functors from $Inj A$ into abelian groups that respect products.


In particular, I wonder whether condition (2) implies (3) and whether (3) implies (1). If these implications do not hold, are there any "natural" additional conditions that could be added to make them valid?


Also, does condition (3) (possibly, combined with (2)) have any "nice" reformulations or consequences? Does it possess any "natural strengthenings"?


Any hints would be very welcome! Is there any text where I can read about these matters ("classical" books on abelian categories do not help much)?


My motivation comes from the study of the heart of compactly generated $t$-structures (and more generaly, $t$-structures of finite type); $Inj A$ is related to the right adjacent weight structure, and condition (2) comes from the existence of a "left orthogonal" weight structure satisfying "nice conditions".


P.S. Professor Rickard has given a very nice example demonstrating that (3) does not imply (1). Certainly, any other enlightening examples would also be very welcome! 


P.P.S. Certainly, a functor (of abelian categories) is conservative and exact if and only if it is faithful exact.:)



On various relations between "additional axioms" for AB4 and Grothendieck abelian categories
I don't think (3) implies (1).


For example, the opposite category of the category of abelian groups satisfies (3), but is not AB5.


