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Series 90/135Ω info needed

ratioratio Posts: 2,213Member
So our service guys are stuck on an old church with Series 90 controls, & it looks like I'm going to have to help them out. Does anyone have some literature on them? I understand the basic concept (Wheatstone bridge) & I'm reading all the old ModIV etc. manuals from Honeywell as well as The Engineering Manual of Automatic Control, but I'm hoping for a jump-start on knowing all the tricks & Clever Things the Old Guys used to do.


  • EBEBRATT-EdEBEBRATT-Ed Posts: 6,551Member
    I am old but don't know any tricks on that stuff.

    The thing I have to always remind myself is the r-b circuit when closed will drive the valve or damper in one direction (usually red-blue for btu) and r-w drives it the other way, but the motor balances between the r-w and r-b resistance.

    I usually remove the controller wires and make sure I have 24 volt power to TT on the damper or valve. Jump r-b drive it one way then r-w drive it the other way. Having a manual pot will help.

    If the valve/damper is ok then move on to the controller and it's wiring
  • ratioratio Posts: 2,213Member
    Thanks. This place's been hacked on for decades. Even our guy who had this building was a tinkerer. What's happening is that the outside air damper drives to 100% when the stat satisfies. That ain't working so well now that it's 31 out. The sad thing is that I can't even tell if our guy did this for the cooling season & was planning on undoing it for the heating season. (He's no longer with us, so I can't ask.)

    What I think I'm going to do is build a whole new economizer with demand ventilation. I hope they can afford it!

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