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  1. #1
    Join Date
    Jul 2006
    Location
    Milwaukee WI
    Posts
    700

    Question MR series Selectra modulators

    I have to go back to a make up air unit in the morning where I think I have a bad Modulating gas valve on a make up air unit.

    It runs on LP and I get Pilot and I sens Flame just like I should. It tells me that the Main valve is on but my burner is only 1/3 lit.

    about 23 volts DC to my Modulator (I am pretty sure that means It is supose to be full open) but like I said the burner is only 1/3 lit.

    I know how dumb this might sound to all of you but I cant for the life of me see where to measure gas PSI from on this modulaiting Valve.

    It is close to below Zero Temps up here in Milwaukee WI and I am trying to rule out if a regulator is frozen up or somthing like that before I condem this valve. (I am sure it is not a cheap one)

    I only had 1.5 hours to look at this thing before I had to go home so I am going back tomarrow to look at it closer.

    dose anyone have some any Ideas of stuff I can rule out before I send this valve to the Maxitrol grave yard.

    Its a MR series gas modulator. Main valve is opening I have not varified the exact gas PSI to it yet because I did not find a port to hook up my Magnahelic yet but I know it is at least getting some.

    Most of my hour and a half in to it so far was just finding the thing and shovleing the snow from around it. a little time making sure the LP tank was full too.

  2. #2
    Join Date
    Aug 2006
    Location
    Mixing oil and fire with a big spoon.
    Posts
    4,336
    the MR410, 510 and 610 series decrease outlet pressure with an increase in voltage.
    "Mother" is the name for God on the lips and hearts of children....The Crow

  3. #3
    Join Date
    Mar 2001
    Posts
    1,213
    Look in the window - the indicator should tell you if full open or not. this unit may fire @ negative pressure. Checkyour inlet pressure - you say LP gas - reg could be frozen too.

  4. #4
    Join Date
    Aug 2002
    Location
    manitowoc wisconsin
    Posts
    4,943
    Trying to service electronics without a guide would be like trying to catch a fart in the whirlwind! If you have a mr212 d or e 20 vdc should be fully open.go here & download a guide for the amp you have. http://www.maxitrol.com/w_max__elec_44.htm Also propane is harsh on burners.I have seen them neglected/not cleaned causing them to rust nearly closed.This is a direct fired burner right?You need to climb inside the unit & take a numbered drill & punch out the crud in the burner orifices if it has not been done.Do not ask or take someone's word for it climb in & check.Most mua's I have worked on have multiple taps for pressure reading.I have drilled & tapped an 1/8" npt port in an elbow in a pinch.
    Take your time & do it right!

  5. #5
    Join Date
    Jul 2006
    Location
    Milwaukee WI
    Posts
    700

    Question

    After finding all my gas Pressure ports and checking things out I found this direct fired burner with 13" WC coming from the regulator in to the unit then in to the regulator before the Main Valve coming out I had only 2" Checked the spring and found a brown one that is only good for up to 3" WC but the name plate said 7" I got a tech. support guy on the phone and he told me the name plate is wrong and I should only have between 2.5 and 3" WC I started to did farther and found that someone had cleaned all the ports in the manifold really well recently the thing was a little dirty but not bad.

    I got a little desperate and decided to pull the whole burner out and found the black pipe filled with Ice and soot about a 50/50 mix of both all the way through the burner back in to the modulating valve.

    I tried like hell to clean it all out but ended up replacing the burner and Modulator valve and re-pipping the thing.

    Im a little confused on how to set the Gas PSI right.

    The Tech. guy told me with Propane they run the PSI lower and keep the same orifices sizes in it, That in its self seems funny and I have a feeling that it is the real cause of all my soot. But I guess I got to go by what he says.

    If set this thing up just like he told me 2.5" WC in-let set my Modulator for the right Delta-T in high fire and then set low fire with a low ribbon all the way across the burner, How do I really know if I am still sooting inside this thing or not.

    or can the be other causes of the soot that I am just not thinking of right now.

  6. #6
    Join Date
    Mar 2001
    Posts
    1,213
    Have you gotten the history of this unit??? Perhaps it's never been properly set up. Did you check the airstream with an analyzer? You may need to raise your low fire to clean up the flame. What make of DFMUA?

  7. #7
    Join Date
    Oct 2002
    Location
    Lady Lake, Florida
    Posts
    799
    At first I was curious if he was fixing a reznor but I suppose since there were orifaces on the burner plate I suppose not. I'm curious too what brand DFMUA he is working on.

  8. #8
    Join Date
    Jul 2006
    Location
    Milwaukee WI
    Posts
    700
    Manufacture was a RUPP.

    As far as being set up right in the first place. I talked to the Tech who installed it over 5 years ago and he rememberd the Install but had no Idea what I was talking about with the Gas PSI at only 2" WC

    I have a feeling he never checked it, He was like me and was shocked that the nameplate said seven but the regulator only alows 3 at best.

    I wish I had the modle # but I tossed my feild notes allready. (another lesson learned the hard way) I can get it next week some time. I said I would go back and check on it in a few days. I got class for the next 2 days so I dont have time right now

  9. #9
    Join Date
    Jul 2006
    Location
    Milwaukee WI
    Posts
    700
    As far as size of the unit I dont know for sure it was very small only 3/4 gas line.

  10. #10
    Join Date
    Oct 2002
    Location
    Lady Lake, Florida
    Posts
    799
    Ah ok. I think it is possible that 7 may mean a min. allowable gas pressure of 7"w.c. to the unit. I know most large reznor DFMUA units have an min and max allow pressure range. Never worked on RUPPS except mobile temp heaters.

  11. #11
    Join Date
    Jul 2006
    Location
    Milwaukee WI
    Posts
    700
    Dose all this really make sense??

    Lower Gas PSI but keep orifice the same,

    Don’t get me wrong I have only had one semester of any real education in HVAC, but when we talked about atomizing and BTU content this is just backward from the way I was understanding.

    My only real concern is being sure it dose not soot up again in the next five years. Right now the Maintenance department thinks Im a hero for getting this thing going and this may be my first regular customer and I don’t want to screw it up right off the bat.

  12. #12
    Join Date
    Oct 2002
    Location
    Lady Lake, Florida
    Posts
    799
    I would recommend recording the unit info and have your local rep fax or e-mail the installation, start up, and operation and maintanance manuals and go thru the unit as if you are doing a full start up and tune. Believe me I've come across a few DFMUA units that had been started up and operated by people who had no business starting a woodburning stove much less this equipment. It's a great learning opportunity.

  13. #13
    Join Date
    Jul 2006
    Location
    Milwaukee WI
    Posts
    700

    Thumbs up

    Thanks for everyones help, This hole job with this thing has been a great confidence builder and learning experience for me.

    I will do a combustion test on it next week.

    part of me wonders if maybe they ran out of LP and it sooted up while running low and without properly cleaning it things got a little pluged up and the whole soot effect just snowballed out of controle.

    I feel pretty good about the hole thing, only 6 months ago I did not even know what a direct fired Make up air unit was.

    I have allready talked to the parts house about getting the start up guides.

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