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Honeywell L91A Proportioning range?

I had been under the impression for a while now that the L91A had a fixed, additive, differential of 1.5 psi. However I just re-read the manual, and it seems that the differential is only 0.5. But it's not clear in the manual if it's additive, subtractive, or both.

I'm guessing it's the latter, so that if you set the main to 1.5 psig, the proportioning range will be 1.0 - 2.0psig. But that's just a guess. If someone can enlighten me, I'd much appreciate it. I did some searching and couldn't find any answers here , or on google, or the Honeywell site..

Energy & Sustainability Engineer


    EBEBRATT-Ed Member Posts: 9,190
    edited December 2016
    Sorry, I do not know what the L91A differential is but you are correct that it is a fixed differential. According to the manual it is .5 psi which I feel is much to close of a differential. It will cause the mod motor to "hunt" in most applications in my opinion. I would guess that it is subtractive.

    I dislike that control for that specific reason because the diff is fixed. and seldom used it.

    I always use the L91B which has an adjustable differential, works much better
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