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  • Blodgett Convection Oven

    Posted by guest on August 5, 2015 at 12:00 am

    I have a Blodgett Convection oven.  Blower was operating but not heating.  While checking the electrical I just pulled the igniter cable off and it began arcing.  I reattached the cable and cycled the unit from 0 degrees through 400 and it called and satisfied normally through the entire heatup.  I left, about an hour later, the customer called back and it wasn’t heating again.  I’m thinking there’s an issue in the ignition circuit in the cable or in the igniter or flame sensor itself.  Maybe the ignition module, but I don’t think so.  Haven’t been back yet, thought I’d run it by you guys.

     

     

     

    I can’t read the model or serial number, but the ignition module is a Johnson G670AW-1  How can I locate part numbers to order?  Are these pretty much standard parts across the varying models?

    fixbear replied 5 years, 3 months ago 1 Member · 9 Replies
  • 9 Replies
  • mroadman

    Member
    August 5, 2015 at 7:58 pm

    sounds like an old DFG oven . Part number for new module is 20348 . It is now a Fenwal module . Honeywell replaced the Johnson and Fenwal replaced the Honeywell a few years ago . Make sure you connect all the ground wires . Instructions for the conversion come with the part .

  • ectofix

    Member
    August 7, 2015 at 6:17 am

    Thanks mroadman.  I didn’t know Honeywell modules were in the Blodgetts at one time.  Somehow I missed that.  I saw the JohnsonControl modules for years and I still have a transducer for testing their flame current.  All of our Blodgett ovens NOW have the Fenwal module.

     

    dallas, yours sounds like an intermittent problem.  Oftentimes, that’s attributed to poor flame sensing.  Merely observing the ignition trial will tell you of that problem.

    Over time, the flame sensor rod will develop oxidation which tends to “insulate” (for lack of a better word) its ability to conduct flame-rectified current.  The evidence of this can be observed by simply watching it (vice taking an actual flame current reading).

     

    To do this, remove the kick panel.  Turn the unit on.  As the thermostat calls for heat and powers the ignition module, watch the pilot light up:

     

    If there’s good flame current, then the spark for ignition will stop within a second or so and the main burners will come on.  All is well. If there’s poor flame current, then the spark for ignition will continue for a much longer duration although the pilot is obviously lit.  These extended ignition trials may vary in duration between one call for heat to the next.  That’s a sure sign that the circuit is struggling to prove flame.

     

    The Fenwal will trial for ignition for up to 50 seconds.  SO…that’s how long the module may spark in order to prove flame.  I’ve seen them take ten…fifteen seconds before proving flame – due to an oxidized flame sensing rod.  I’ve also seen the same oven spark that entire 60 seconds, never prove flame, retrial several times and then lock out.  Bear in mind that, as the module acknowledges the presence of a flame, it will stop sparking.

     

    The usual culprit is the flame sensor rod itself.  You can remove and polish it with emery cloth or a Scotchbrite pad.  I always keep a extras handy, so I simply replace it.  Of course, all flame circuit connections need to be clean and tight – including ground.

     

    Here’s a nice little PDF by RobertShaw that explains flame rectification:

     

    http://www.uni-line.com/spaw2/SiteContent/150-2163_RevB_1.pdf

     

    Here’s a video which explains the Fenwal module’s sequence of operation:

     

  • ectofix

    Member
    August 7, 2015 at 6:42 am

    FYI, the JohnsonControl you have will operate in a similar fashion.  You won’t be able to read flame current with your meter without a transducer, since the JohnsonControl flame current is lower than the capabilities of the μa setting on your digital meter.

     

    Here’s a chart depicting the Fenwal’s sequence of operation that’s in that video:

     

    http://www.blodgett.com/wp-content/uploads/20348-Sequence-of-Operation1.pdf

  • ares

    Member
    December 16, 2018 at 10:43 am

    Also look inside burner compartment where the electronic pilot mounts to the burners, if I had a nickel for the number of times Ive found chunks of the combustion chamber insulation sitting on top of the electrode and flame sensor causing it to short to ground thus resulting in ignition failure, I generally use the longest screwdriver in my box to poke the offending piece of insulation off of sensor and over to the side of combustion chamber. Also check the entire length of ignition cable for tiny cracks or pinholes, causing high voltage spark to short to ground, I find that quite often on the “newer” thinner orange ignition cables, use your ears and listen for arcing, or just run your fingers along it, you’ll find it.

  • fixbear

    Member
    December 16, 2018 at 5:33 pm

    ares wrote:

     

     or just run your fingers along it, you’ll find it.

    I about choked on my drink when I read that.  Course your hand and arm are going to pain you for a bit till the feeling comes back. 

  • fixbear

    Member
    December 16, 2018 at 5:36 pm

    I get a blodgett 404 on that linc

  • ectofix

    Member
    December 16, 2018 at 7:29 pm

    fixbear wrote:

    I about choked on my drink when I read that.  Course your hand and arm are going to pain you for a bit till the feeling comes back. 

    LOL!  I don’t like dancing to the unintentional beat of twenty-thousand volts coursing through my body EITHER!

    fixbear wrote:

    I get a blodgett 404 on that linc

    This thread is three years old.  I hope dallas has solved his problem by now.

     

    Blodgett has altered their website since then to shut down access to their technical stuff.  I hate that THAT is the nature of things nowadays.  Being in-house, I gotta get more resourceful.  Glad I got most of what I need already.

  • ectofix

    Member
    December 16, 2018 at 7:35 pm

    Here’s the chart I was referring to:

     

    DFG-100 Ingition Module Sequence-of-Operation

  • fixbear

    Member
    December 16, 2018 at 8:25 pm

    I really don’t understand that mentallity.  It’s why I steer my customers away from certain brands.  After all, they are not really making money on repairs.  But if you have a local person willing to learn and keep the customers are happy.  And never has a complaint from the customers,  why not support him.  I realize that some owners try to fix things that are over there head.  And that can be dangerous for sure.  Good brands were never a problem,  just a call and set up a account.  But others just want it in house like Hobart and Baxter. Many years ago Globe was like that, but changed over time.

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