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  1. #1
    Join Date
    Nov 2013

    Pneumatic multizone units

    On a service call today I had a complaint of an area being to cold and it sounded like the system was shutting off at 4 pm. I reset the time clock and the boiler came on and the operating control cycled the boiler off at 148. I checked the hot deck temp and found it was only getting up to 82 degrees, then dropping down to 75. 3 of the five zones where sitting at 8 psi, one was at 20 and one was at zero. The one zone at 20 psi I turned the temp up to 73 and the pressure dropped to 16 psi.The little amount of work I have done with pneumatics I thought that the hot deck should be set to 95 , when I opened the panel door there was a control that said hot deck and both gauges were at zero. One gauge was on a spot labeled "b" and the other gauge was on a spot with a number three. I did not see a dial on this but is that the item that I would need to raise the hot deck temp? Is there a site I can start learning about the basics and get a better understanding of these controls?

  2. #2
    Join Date
    Jan 2007
    Stongsville Oh
    Your best bet is to start by getting ahold of the controls diagram if it even exits. If not trace and make your own diagram, Then analyze. Write down all components part numbers and start googling or go to supply house for data sheets. Hot deck cold deck multizones many times used hi lo signal selectors so the hot deck temp is set by the coldest zone (all t/stat branch lines go to selector inputs and unused ports are jumpered. Branch line of hi lo selector to cpa port of receiver controller ( remote set point adjustment). Receiver controller has hot deck sensor and branch line goes to N.O. valve. Pressure at valve indicates hot deck temp is in throttling range. Zero pressure valve is being told to open and raise hot deck temp. There are variations depending on who's controls but principle is the same.
    I didn't write the book I just read it!

  3. #3
    Join Date
    Sep 2008
    Western PA

  4. #4
    Join Date
    Apr 2008
    Quote Originally Posted by ckartson View Post
    .. Hot deck cold deck multizones many times used hi lo signal selectors so the hot deck temp is set by the coldest zone ...
    Ah yes that common simple way to pass on 'zone of greatest demand.
    ..Or the most out'a whack t-stat in the joint
    2nd worst only to 'return air H/D reset

  5. #5
    Join Date
    Feb 2010
    The honeywell grey manual covers basic pneumatics and is probably available for download. The Robertshaw pneumatics manual was what I used years ago (pre DDC) but that's been out of print for some time I believe.

  6. #6
    Join Date
    Jun 2013
    Still Ned more?

    Clev oh terry k is a 50 yrs exp 72 yr old still training

    EMail avail in profile for his #s

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