MemberJuly 15, 2021 at 2:03 pm
I have a VC44GD Vulcan convection oven where the top oven is having it's ignition sequence chatter.
I originally thought it was an igniter issue, so we replaced it then the ignition board, then we traced it back to the switch inside the motor and replaced it and then thought it was the thermostat control board and replaced it, then the thermostat probe and still, it does it.
It seems to be the switch inside the motor (which we replaced) but I don't understand why it's acting up.
On low, going into the motor I have 120V, coming out, I have 94V which is where the ignition relay chatters, then when I switch the speed to high, it becomes 12V and it won't chatter as it won't even try to pull in.
It's driving me nuts, any ideas? Other than spending another $1200 on their new latest and greatest motor?
MemberJuly 15, 2021 at 5:45 pm
Sounds like the contact points of the centrifugal switch are either coated with a foreign substance, or the switch isn't properly adjusted for the throw of the weight unit. The weight unit pulls away from the movable contact at speed. Allowing it to close. And they are not supposed to touch once speed is achieved. It's not uncommon for the wear on the contact point, and the placement of the new contact to need a tweak with either a shim or bend. Check by manually lifting the weight against the stop and look for a air gap. also make sure the sliding ring is not tight or loose and wobbling. The weights may go out, but does the ring go forward and allow the point to seat? Moving parts on a rotary member are always a problem.
MemberJuly 15, 2021 at 5:49 pm
BTW, I come across a lot of Century and AO Smith motors that when the switch manufacturing moved overseas, the replacements were off considerably.
Hate cooperate buy-outs/takeovers.
MemberJuly 15, 2021 at 7:15 pm
One other thing, are you certain your measuring the switch leads? The results you posted sound like a motor winding. Specifically the low speed winding. On high the 12 volts you see would be induced.
MemberJuly 15, 2021 at 8:27 pm
@ectofix No, reading from hot leg to neutral.
I looked into this more, I gave it some thought, stared at it, hit it with something and had an idea.
When I opened the motor back up to look for myself (someone else changed the switch inside) I started messing with the actuator part itself, I noticed it moved on the shaft which seemed a bit off, there's about 1-2″ of space where the actuator can move back and forth, which in theory could make it loose contact with the switch.
I checked the actuactor and it had a crack down the center where it sits on the shaft, so I figured it could be. To me, since the low to high made a difference and it seems to have to be hot before the problem really appears, I figured it could make sense that it was just moving enough to partially open that safety by sliding away from the switch.
I 3D printed a spacer to put on the shaft that sits between the top of the actuator and the snap ring which will prevent it from sliding around. So far it's not making noises like it was before, but the true test will be tomorrow when it's on for most of the day.
I'm 100% sure I'm measuring the switch in the right place, I can't buy the motor and I definetley can't buy the actuator. I'd have to buy the “new and improved” version which is a new motor and blower wheel.
The mechanism itself works every time, I set it up in my shop so I could ohm the switch when it runs and see the actuation when it happens, it's gotta be either the switch itself or that actuator.
Prior to making the spacer, I put it back together to see if it was moving and when it's actuated, the top of the actuator was riding on the switch, which I believe is wrong, after putting in the spacer, there was a 1-2MM gap, so it seems to have made a difference.
Time will tell.
I've been throwing parts at this thing but so far nothing has worked, I really didn't think it would be so complicated.
MemberJuly 19, 2021 at 7:31 pm
Seems like this might have done it, haven't heard of a problem for the last 3 days, which so far is the longest by far since starting the repair.
Thanks for the assistance, if the problem isn't fixed, i'll be back 🙂
MemberJuly 20, 2021 at 5:35 am
Glad you got it. I've never seen the centrifugal crack before. Is the counterweight still in tack to balance it?
MemberJuly 21, 2021 at 12:03 pm
Yeah, it's odd, it seems to be functioning as it should, it was just easy to move around.
I think the counterbalance was in place, I didn't specifically check but nothing seemed to be missing when I inspected the rest of the piece.
MemberJuly 21, 2021 at 1:10 pm
I once saw one that had a vibration of the fan. That in turn made a spot weld of the counterweight break and short the windings.
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