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  1. #1
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    Nov 2005
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    T991A controlling gas valve

    I have a T991A modulating stat controlling a honeywell fluid power gas valve type:v9o55a 10552. problem i'm having is the t991a is set for 70* with a 3* diff. the gas valve bottoms out on low fire then goes out on the fire eye. i've tried to adjust the low fire dial inside the gas valve but no luck.

    i've moved the stat setting higher with a 15* diff and it doesn't bottom out. i'm almost certain i have a bad t991a stat? and what do you guys set your diff setting for on that type of stat? this is a direct fired mua.

  2. #2
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    Quote Originally Posted by -frozen-ocean- View Post
    I have a T991A modulating stat controlling a honeywell fluid power gas valve type:v9o55a 10552. problem i'm having is the t991a is set for 70* with a 3* diff. the gas valve bottoms out on low fire then goes out on the fire eye. i've tried to adjust the low fire dial inside the gas valve but no luck.

    i've moved the stat setting higher with a 15* diff and it doesn't bottom out. i'm almost certain i have a bad t991a stat? and what do you guys set your diff setting for on that type of stat? this is a direct fired mua.
    Sounds more like you have a issue with flame stability on low fire. Do you have a interrupted or intermittent pilot primary? UV or rectification?

    I going to assume you are interrupted. Remove r on the actuator. Then jump r and w together. That will be true low fire. Then visually inspect the flame characteristics of the burner. You need to have the lowest flame length with minimum flame cutout.

    How clean is the burner? Are the orifices clogged? Are the plates clean? What's your fps across the burner? These all affect minimum fire.

    Also keep in mind true minimum fire on that actuator is only adjustable from about a 1/10" to 1/2". By setting the stat to a high temp with 15 differential, all it did was increased the your range. You did not increase the minimum fire of the valve. You need to adjust minimum by the instructions above.

  3. #3
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    Nov 2005
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    well i set it to 80* with a 15* diff for awhile just to see, and it didn't bottom out like it did with a 70* with a 3* diff.

    this does have a piliot reg with a solenoid. a direct spark with a flame sensor.
    but i'll forsure to check out what you have stated in your post. what fps reading should i shoot for? this is an older eng-air with a summer/winter switch a t991a to control heating and a duct stat to control a/c. when its cold out i have no problems. seems like when it warms up abit problem starts.

  4. #4
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    Quote Originally Posted by -frozen-ocean- View Post
    well i set it to 80* with a 15* diff for awhile just to see, and it didn't bottom out like it did with a 70* with a 3* diff.

    this does have a piliot reg with a solenoid. a direct spark with a flame sensor.
    but i'll forsure to check out what you have stated in your post. what fps reading should i shoot for? this is an older eng-air with a summer/winter switch a t991a to control heating and a duct stat to control a/c. when its cold out i have no problems. seems like when it warms up abit problem starts.
    When it warms up outside, then the unit is actually going into minimum fire. Hence why I think, you have a minimum fire problem.

    Put the actuator in true minimum fire, and see what that burner is doing. I have a feeling, you will see the flame disappear or only be in certain sections of the rack. The hardest place to keep a good flame is at the ends of the burner rack and that is where your flame sensor is.

  5. #5
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    Jun 2008
    Location
    Windsor, Ont.
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    500
    I tend to agree with ascj, and his suggestion to jumper r-w at the V9055 actuator and set the low fire should prove it. I've replaced a few of them (V9055's that is) just because the minimum position potentiometer internally is flaky and wouldn't hold a setting.

  6. #6
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    Nov 2005
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    My mistake. this is a indirect fired unit with a heat exchanger. I found the wrong t991a installed. it was averaging and called for fast response on the print.
    Also found mp100 module and mart 1 amplifier on fireye. which should of been mp101 module and a mart 1 t amplifier.
    this unit has a eng air 109-2 interface which i guess senses low fire for about 2 min then shuts off the burner. not too familer with this interface.
    I guess when it got warm outside the interface was sensing low fire and shutting off burner. with the wrong module and amplifier installed it would lock out. make sense???? i even installed a 135 ohm potentimoter across
    v9055a gas valve and it did hold at low fire. do u think if the interface senses low fire alot and shuts down burner i could be getting alot of lockouts?

  7. #7
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    Jun 2008
    Location
    Windsor, Ont.
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    What version of control system operates the unit? Is it a G-Trac? Which burner does it have? I haven't worked on 1 in a while but from what I remember the G-trac control monitors call for heat based on discharge temp and will cycle the main gas off for a few minutes allowing the burner to run on pilot only and if a call for heat does not occur within that time period it cycles the burner off.

  8. #8
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    this unit is from the 80's. the t991a is the control system. lol. all it has is a summer/winter switch a t991a for heat with a 109 -2 interface. a outside air stat set for 68. then has a duct stat for a/c with a outside air stat set for 50 for low ambient. thats it for controls.....

  9. #9
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    Jun 2008
    Location
    Windsor, Ont.
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    I'm assuming you have this info on hand (see link), older Engineered air systems had very poor turndown capability and to compensate for that they cycled the snot out of the burner. Problem being if you have inconsistent ignition you get lockout. Their control system is very basic (maybe a little too basic), any of the units I have had problems with were usually due to intermittent pilot ignition cycles and once that was solved all my problems went away. Hopefully someone else has some more direction for you.

    http://engair.com/manuals/Q7LxO1a22.pdf

  10. #10
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    So I take it, that it has a standing pilot? I hope so if your are using a MP101.

    The MP100 can be used just like the MP101. For a standing pilot there is a wire you have to cut.
    So it sounds like the primary was replaced with a MP100 and the wire wasn't cut. So when the burner shut down, the primary sensed flame signal and locked it out. So by replacing the primary with a MP101, you fixed that.

    But if that was the case, you have just snipped that wire.

  11. #11
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    Nov 2005
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    i havn't changed out those parts yet. its been real cold out so no problems as of yet. the pilot has a solenoid valve with a reg. the unit has a dg burner gordan prait. i talked to tech support about problem told them what parts were there, they told me to use the mp1o1 and the mart1t. . u would think he is right though? the interface shuts down the main gas valve which kills power to the pilot circuit also. he said it would cause nosense lockouts with the parts that were in there. this unit originally had a old tfm 1d flame relay which was stated on the original print. years ago the fireye went in for replacement i take it.

  12. #12
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    Quote Originally Posted by -frozen-ocean- View Post
    i havn't changed out those parts yet. its been real cold out so no problems as of yet. the pilot has a solenoid valve with a reg. the unit has a dg burner gordan prait. i talked to tech support about problem told them what parts were there, they told me to use the mp1o1 and the mart1t. maybe the guy got confused on the model of the unit???? i'll phone back on tues. u would think he is right though?
    Does it have a standing pilot? That is what that primary is used for. And like I said the MP100 can be modified to work like a MP101.

    I have worked on Gordan Piatt burners, but never have run across a DG.

    The MART1T is just a faster responding amplifier. Won't make much difference.

    Can I go back to the beginning, since I got some more info. We are dealing with an indirect. With a power gun. When the unit locked out, was it trying for ignition again? If it was, then what was you flame signal.

    If it locked out right when the burner shut down, then what was your flame signal.

    That primary will only lock out if the pilot does not prove during "pilot trial for ignition" or it senses flame signal when not in "pilot trial for ignition". Unless the one wired is cut. Then it would ignore the later, just like the MP101.

  13. #13
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    Quote Originally Posted by nyrb View Post
    I'm assuming you have this info on hand (see link), older Engineered air systems had very poor turndown capability and to compensate for that they cycled the snot out of the burner. Problem being if you have inconsistent ignition you get lockout. Their control system is very basic (maybe a little too basic), any of the units I have had problems with were usually due to intermittent pilot ignition cycles and once that was solved all my problems went away. Hopefully someone else has some more direction for you.

    http://engair.com/manuals/Q7LxO1a22.pdf
    BTW- Thanks for the read.

    Wow, what a POS setup.

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