Pronunciation of CH

[SKG_Scintill]

Yes I know, I don't ever come in this subgenre and already 2 threads? Whatever :P

I've been trying to figure out why it is that in some cases the diglyph "ch" is pronounced as a "tsh", in other cases as "k" and in even other cases as "sh": "chimpansee", "chiropractor" and "chic", respectively.

At first I thought it could be the vowel after "ch", but as just was shown, that certainly isn't true. Nor the consonant after "ch[aeiou]".
On the other hand, when "ch" is followed by a consonant, so far it's always been pronounced as a "k" (chrome, chlorine, chronic, etc).

I have yet to research the etymology of the words, if the land of origin is of any cause. That is research for another time.

Does anyone happen to know or have ideas as to what causes the difference in pronunciation?