"Went straight up as if from a factory" <---- for the word "as" in this sentence should I say it like /æz/ or like /əz/ ?
Both [æz] with stress, and [əz] without stress, sound fine, to me (I'm a native English speaker). But the stress does matter. You can't stress the [əz] version and have it sound like normal American English (I can't say about other dialects).
I've used brackets for your examples instead of slashes, since the variation between the vowels [æz] and [əz] that you're asking about concerns phonetics, not phonemes, and by convention, slashes are used only for phonemic forms. There is no phoneme /ə/ in English (though some might disagree with this).