The vowel in the prefixes <com-> and <con-> is, as you would expect, usually ə if the syllable is unstressed. Examples:
commodity compartment complete comply condition congressional connect continue consider contextual
If the prefix has a main or secondary stress the vowel is usually ɒ. Examples:
ˈcombat ˌcombiˈnation ˈcommodore ˈcompetent ˈconference ˈcongruous ˈconquer ˈcontinent ˌcontiˈnental
However, there are some words where the prefix is stressed and the vowel is ʌ. Examples:
comfort comfortable compass conjure
Finally, there are a few words where the vowel is ɒ for some speakers, but ʌ for others:
comrade constable
2013_09_26