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Thread: How do I test Millivolt valve system - Pilot is on, but main burner not lighting

  1. #16
    DIY Senior Member mnalep's Avatar
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    Let's try that link again:

    http://americanhvacparts.com/Merchan...tegory_Code=GV

    I do not have a schematic for that replacement gas valve(GSV820A1047A), but you can see it lists my current one (VS87A9X4X2) as one it replaces.

    When you state "The internal valve coil must then be connected to the topmost and bottommost of the four terminals." (SO THE VALVE COIL is CONNECTED TO WHICH 2 terminals in my picture)?

    Also, you made me think that my physical valve actually has 6 screw in terminals? I have never learned to read a schematic, but it seems to indicate 4 terminals?

    Also, the two steel plates on the physical valve terminals are 'jumpered 'from a pile generator(RED) to (thermostat)TH1, and another from the other thermostat terminal(TH2) to a Limit terminal(L2).

    But the schematic seems to me to show one connection from one of the limit terminals (Lx) to a Thermostat terminal(T1 or T2), and another connection from the other LIMIT Ly) to a PILE GENERATOR terminal (either RED or WHITE).

    Am I interpreting the schematic wrong?

    Thanks for that heads up on the CO detectors!
    Last edited by mnalep; 10-25-2010 at 03:33 PM.

  2. #17
    Plumber jimbo's Avatar
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    You should NOT short out the t'stat terminals to check it. There is a heat anticipator coil in there which limits current to the valve, and shorting that out can damage the valve.

  3. #18
    Homeowner Thatguy's Avatar
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    6 terminals + 2 jumpers = 4 effective terminals = 4 nodes
    http://en.wikipedia.org/wiki/Node_(circuits)

    You need to find out which terminals on the replacement valve go to the coil. I couldn't make it out from the link but if you can get a photo of the terminals their labelling might tell you, or if their cust. service rep has one handy, he/she can read it to you.
    Last edited by Thatguy; 10-25-2010 at 04:42 PM.

  4. #19
    DIY Senior Member mnalep's Avatar
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    Jimbo, Thanks for that tip. I tried that once already, but I won't again.

  5. #20
    DIY Senior Member mnalep's Avatar
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    thatguy,

    Here is a white-rodgers replacement millivolt gas valve installation instructions:
    http://www.emersonclimate.com/en-US/.../0037-6264.pdf

    Page 3, FIGURE-3, has diagram of the wires and seems to show where all 6 wires would go. ;-)

    now I would just need to verify if the input is 3/4" (which I think it is), or 1/2". I think the output is 3/4" also. Besides me taking it apart, is there any way to tell from the picture, or somewhere else online?

  6. #21
    Homeowner Thatguy's Avatar
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    In figure 3, TH and PG should be the coil connections and probably measures about 3 ohms. I don't know what they mean by 'power unit' or how this terminal ties in to the rest of the circuit.

    The Figure 4 wiring is a series circuit and makes perfect sense.
    Last edited by Thatguy; 10-27-2010 at 07:25 AM.

  7. #22
    DIY Senior Member mnalep's Avatar
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    Figure 4 is 24 volt. Fig 3 is millivolt, which I have. I went and looked at this valve at the store, and the 'power unit' is a large nut screwed into the valve body with a black wire coming out the middle of it. If you look at the 2 diagrams on the first page, the one on the right shows the wire, with a slide on clip on the end of it. I think that is the 'power unit'. I don't get it either, but what else could it be?

    When you mention 3 ohms, are you saying I should be ohm-ing these?

  8. #23
    Homeowner Thatguy's Avatar
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    I would use an ohmmeter to confirm what terminals the coil is wired to, and what it is not wired to. You want to know where the current goes and how it goes because fig. 3 is puzzling.
    This circuit has to work on paper first.

    If there is only one black wire coming out of the power unit then the case of the valve is being used as an electrical conductor. If your current valve doesn't do this you may need to add a jumper wire.

    Fig. 3 seems to be having the t'stat alone turning on the valve, so the power unit working with the hi limit can somehow disable the valve turning on, but how it does it is not obvious from this figure.

    There may be something wrong with fig. 4. There doesn't seem to be any way to prevent the valve from opening if there is nothing to ignite the burner, unlike in fig. 3 which uses the pilot gen. to supply current to the valve.

    For testing you can simulate the t'pile with a 1.5 v "D" cell and two 3.6 ohm 1/4 w resistors from Radio Shack.

    The "power unit" could be an 18 mV thermocouple but it is not clear to me what function this serves.
    Last edited by Thatguy; 10-27-2010 at 03:45 PM.

  9. #24
    DIY Senior Member mnalep's Avatar
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    thatguy

    here is another diagram they have for that gas valve.

    http://www.emersonclimate.com/en-US/...pg0250_253.pdf

    Frankly, I'm overwhelmed by this diagram. Can you make sense of it?

  10. #25
    Homeowner Thatguy's Avatar
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    Quote Originally Posted by mnalep View Post
    thatguy

    here is another diagram they have for that gas valve.

    http://www.emersonclimate.com/en-US/...pg0250_253.pdf

    Frankly, I'm overwhelmed by this diagram. Can you make sense of it?
    I know figs. 4 through 14 and fig. 1 don't apply. If fig. 3 doesn't physically look like your valve it doesn't apply either.

    It looks like fig. 2 applies for the 36C03U and you should measure the coil resistance between TH and PG. The terminal TH-PG is just a tiepoint and does not connect internally inside the valve housing.

    Ask them what the power unit is and how it works with the limit switch and how come it only has one wire.
    Last edited by Thatguy; 10-27-2010 at 08:12 PM.

  11. #26
    DIY Senior Member mnalep's Avatar
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    Fig 2 looks like the 3 screw terminal on the valve. Fig 3 cold have been the 'power unit' lead, but this picture shows 2 wires, and the one I'm looking at only has one.

  12. #27
    Homeowner Thatguy's Avatar
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    Quote Originally Posted by mnalep View Post
    but this picture shows 2 wires, and the one I'm looking at only has one.
    And so this figure doesn't apply.

  13. #28
    DIY Senior Member mnalep's Avatar
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    Sorry it took me so long to get back here. I've had some other problems that needed attention.

    So I took apart the pilot burner and orifice, and cleaned it out.

    I took a couple of still pictures of the flame before and after. And a video clip of the flame is posted below also.

    I also bought a new limit switch and installed it, as the old one was looking kind of rusty. You can see the two limit controls side by side below.

    The furnace has still been working well, although we have had temps in the 60's this last week. So it's been a light duty test.

    The pilot generator was putting out about 750mV on my last meter reading. I was worried at first because my initial reading was around 600mV. I took it all apart and made sure it was real clean, and after I put it back in the 2nd tome the reading was at the normal 750mV. Not sure why it was low the first time?

    So I am hoping this furnace is set.

    Thank you guys for helping me with this!!!



    http://img121.imageshack.us/img121/3128/img0253vh.jpg


    http://img607.imageshack.us/img607/7226/img0266b.jpg


    http://img202.imageshack.us/img202/5348/img0267zf.jpg


    http://img829.imageshack.us/img829/2461/img0283ed.jpg

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  15. #30
    DIY Senior Member mnalep's Avatar
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    I would like to get a vacuum in there and start cleaning the burners and heat exchange area. you can see in the picture there is a lot of dust that needs cleaned.

    what is the best way for me to clean? vacuum? brush, steel wool, or ? it seems really dusty right by the pilot flame area, and on the cabinet just under the main burners. any advice?

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