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  • Vollrath convection oven not heating after power surge.  Model COA 8005. Any suggestions?

     ectofix updated 3 years ago 1 Member · 14 Posts
  • guest

    Member
    July 30, 2017 at 12:00 am

    The 2 Elements have 240v to them.  Fans are running. Timer and thermostat status lights on.

  • ectofix

    Member
    July 31, 2017 at 5:11 am
  • fixbear

    Member
    July 31, 2017 at 6:51 am

    Are you measuring the voltage at the element or on the contractor?

  • burtonmac

    Member
    July 31, 2017 at 1:19 pm

    Not sure of exact ohm reading but they check ok for continuity.

  • burtonmac

    Member
    July 31, 2017 at 1:19 pm

    Both

  • fixbear

    Member
    July 31, 2017 at 3:04 pm

    If both elements ohm as 0 or near 0 up to about 10 ohms, and you have 240 volts at the elements, you have heat.  Amp them and you should see current flow.  The  only way there could be no heat is a open element or no voltage. You wouldn’t have voltage at the elements if the contactor wasn’t working. 

  • burtonmac

    Member
    July 31, 2017 at 4:36 pm

    I agree.  Is it possible to have voltage but no current flow to the elements?  I believe it is an electrical issue coming to the power outlet caused by the power surge.

  • ectofix

    Member
    July 31, 2017 at 4:56 pm

    burtonmac wrote:

     

    Is it possible to have voltage but no current flow to the elements?

    Your question should more properly be written as “Is it possible to have voltage but no current flow THROUGH the elements?”

       Answer:  YES.  If the elements are open or there’s an open wire or wire terminal connection meant to supply power to them.

    So…as fixbear had said earlier.

     

    There’s something amiss here.  Since I’m not standing there looking over your shoulder to see exactly what you’re doing, could you please tell me where EXACTLY you’re placing each of the two meter leads to read voltage getting to the elements?

  • burtonmac

    Member
    July 31, 2017 at 8:10 pm

    From one leg of the element to ground 120v and other leg of the element to ground 120v.  

  • ectofix

    Member
    August 1, 2017 at 6:08 am

    burtonmac wrote:

     

    From one leg of the element to ground 120v and other leg of the element to ground 120v.  

    GROUND? 

     

    Ground is not part of the circuit which energizes those elements.  Therefore, DON’T include it in your tests.

     

    120?

     

    In your original question you said you read 240v.  Did you derive that 240v by adding the two 120s together from the readings you described above?  If you did, then that’s an entirely incorrect method.  For that matter, the two 120v readings you took (while IMPROPERLY referencing GROUND) is probably the same 120v line in both readings – and you have lost connection to the OTHER line somewhere – therefore, no heat.

     

    To make proper voltage readings in a 240v circuit, connect your test leads between L1 and L2. 

     

    I’m outta time this morning to elaborate further.  Sound like you need someone with more electrical experience to assist you in troubleshooting.  This evening, I’ll share something with you to help you understand.

  • fixbear

    Member
    August 1, 2017 at 8:47 am

    That explains the confusion with having a element continuity and yet no heat. You should measure across the element legs, not to ground.  The ground is just there for stay electrical protection, not anything to do with the operation of a machine. Measure across the element  ends with a AC voltmeter set to a 0 to 300 volt scale for a true picture of the potential available. Now when you have zero volts,  you can go back to the contactor and re-measure both the output of the contactor and the input.  Phase to phase, not to ground or neutral ever.  Your heat circuit does not use neutral.  If you were troubleshooting a 120 volt control circuit, then you would use the neutral, but never ground.. IF you have good elements,  You are going to find either a bad pole in the contactor or a open feed from the contactor to the element. Providing the contactor is working, which should be as you had voltage at the elements.

     

    Please realize that the element is no more that a wire.and if you are testing to neutral or ground both ends will read the same voltage unless there is current flow if there is any open on one leg.

     

       Grounds are on all machines for one reason.  That is for life protection from stray currents and voltage.  This includes Static,  Induction,  and shorts from wiring. They are never to be used as a current carrying device.  One checks ground only to determine if it is safe to touch or work on something. Never for circuit testing. Today they are also used for elector-magnetic shielding for sensitive parts (radio,radar, micro waves).

     

    Hope this helps you.

  • burtonmac

    Member
    August 1, 2017 at 9:01 am

    Yes. Big help.  Im lacking in electrical dept esp on 240v.  That explains zero volts across the two element legs.  Let me go back and check the contactor again which was my original diagnosis.  So if im getting a zero volt reading on incoming lines to the contactor would that mean I have an outlet or breaker issue??

  • fixbear

    Member
    August 1, 2017 at 3:05 pm

    That is correct, you must have lost one phase. The supply should be on a 2 pole breaker with a common bar so that if one trip’s, it trips the other. Having 120 volts means one leg is still working.  Your wiring diagram shows that this machine uses 2 poles of s 3 pole contactor for switching L2 only.  L1 is direct connected to the elements.  Referee to wiring diagram linked above for 40702 model.  Hence your 120 volt reading at each end of the element to ground.  Yor have to go back to the terminal block where the number 6 wires come in to the machine and measure terminal 1 (L2) to terminal 2 (L1) for incoming voltage. Optionally for a quick check you can measure across the top of either 1L1 to T1 on the contactor or L2 to T2 and it should show line voltage or zero if the contactor is energized.

     

    The timer and the door switch, and the thermostat all have to be on for heat contactor to work. You stated earlier that the fans were working and the timer light was on. so how about the bake light? If not, the control thermostat (B1)  is open.

  • ectofix

    Member
    August 3, 2017 at 6:05 pm

    burtonmac, please share what you found to be the problem with those of us who made an effort to help you.

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