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  1. #1
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    RATIONAL oven has me IRRATIONAL

    An SCC-202G. Natural gas. My head hurts from banging it against the wall due to a repeated problem.

    DISCLAIMER: I ain't been to Illinois or to CFESA for a week-long tech course. But, I'm our (only) duty expert on our 26 Ration combi-ovens.

    PROBLEM: The upper AIR burner keeps melting the plastic burner blower wheel and plastic air/gas mix components.

    PREVIOUS OCCURENCES: Over and over again...

    I'd originally reasoned out a plausibly possible cause. I thought the original occurrence was nailed down and had posted THIS> http://hvac-talk.com/vbb/showthread....ven-REVALATION. THAT was truly happening.

    I was all about the poor blower connections and a "RESET GAS" displayed to give indication. However, I thought I'd resolved all of that. YET, several subsequent repair efforts...with OTHER reasoned-out causes...and it keeps happening. I'm to my wit's end on this.

    THE LATEST: I replaced the gas valve along with everything comprising the entire burner-blower assembly as it mounts to that heat exchanger flange (with the two tabs and the two little bolts) in the side compartment. New wire harnesses. I remove/inspected that "metal mantle" type burner (I forget fancy name for that) each time. New ignitor/flame proof parts. Nothing blocking the exhaust. The CO2 screw set and then adjusted based upon a combustion analyzer's readings. Lighted off and was "cruisin' like a Cadillac" during the FUNCTION TEST and actual operation as an OVEN.

    Yet, less than a week later...with no RESET GAS popping up to give some warning, the kitchen called it in due to a...uh...NOISE. Sounded like a monster on the other side of the wall with a belly-ache. Got there and got behind the side cover and, sure enough, the plastic burner-blower's mixing chamber cover had melted AGAIN!

    This sounds amateurish, but I have a custom-made, metal blank-off plate especially for this oven...that has nearly assumed a permanent home to cap off the upper air heat exchanger from the side compartment. So once AGAIN, The burner blower and gas valve assembly is merely suspended behind the side panel by some large, UV-rated cable ties, completely disconnected from any electrical input, as the assembly hangs there only to serve as a cap for the four-TORX-screw flanged gas line connection.

    The kitchen staff have subsequently gotten very familiar with pressing the RESET GAS key when it pops up. Although not a huge issue on a normal day's workload, they've OBVIOUSLY screamed about it when they rarely load it top-to-bottom with meat product and the temperature dramatically drops.

    ANY Rational factory-trained folks out there willing to share some ideas?
    ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° °

    "You never know what others don't know." -

    If I can't laugh at myself...then I'll laugh at YOU! -

  2. #2
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    Confirm there is a fresh intake of cool air.

    The SCC 202 ovens have intake at back about 1/4 way up. If air intake tenperature exceeds a certain amount, it will cause the air mixing plate to melt

    This has been proven to happen if hoods aren't correct in some way. Exhaust gases from oven can go down behind oven and be sucked back into intake and cause the intake air temp to get too hot.

    Maybe a peice of equipment is causing it?

  3. #3
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    Quote Originally Posted by Protocol. View Post
    Confirm there is a fresh intake of cool air.

    The SCC 202 ovens have intake at back about 1/4 way up. If air intake tenperature exceeds a certain amount, it will cause the air mixing plate to melt

    This has been proven to happen if hoods aren't correct in some way. Exhaust gases from oven can go down behind oven and be sucked back into intake and cause the intake air temp to get too hot.

    Maybe a peice of equipment is causing it?
    I appreciate your response. I'd checked that little air inlet and knocked away any fuzz. The air duct hose is clear. The exhaust gas is straight up into the hood...as is the steam. There's only a Traulsen cooler in the corner to the left of it and only a rarely used four-burner stove to the right. A tilt skillet used primarily as bain marie to heat bagged stuff to the right of THAT. Nothing else.

    Nothing has changed between mid-December and earlier. I'd had this issue with BOTTOM air burner once before, but replaced everything and address the blower wiring problem...and it's been fine. Yet, this TOP air burner has kicked my a$$.

    Last night, I thought to maybe check out the camera snake, remove the burner and stick it in there to inspect the inside of the heat exchanger. Well today, I didn't and I was too busy to even think about it.

    My manager knows I'm pretty good at what I do. SO...when I told my immediate supervisor yesterday that I CONCEDE and that someone else needs to take a look at it, he then told our manager, who subsequently approved a *certain* service company to come out. I'm meeting with *them* at the oven as their first call Monday morning (I'm taking some time off until then. 54 to 60 hour work weeks for seven months straight has worn my old butt out).

    Badbozo would be tickled to know what company I'll be learning my lesson from. Probably something simple.
    ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° °

    "You never know what others don't know." -

    If I can't laugh at myself...then I'll laugh at YOU! -

  4. #4
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    Oh gawd. We have nothing to do with any branch but our own.

    I remember something from the last class I wrote down regarding this. I'll see if I can dig up my notes.

  5. Likes ECtofix liked this post
  6. #5
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    My notes say that the burner input air hose is off or perforated, or there's some strong reverse airflow (duh), and check burnerbox at tripleweld for hole.

  7. #6
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    I wonder if the gas pressure is dropping over time...

    Things to check...

  8. #7
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    Badbozo, thanks for pulling all of that up and responding.

    I'm thinking that I'm not seeing the forest for the trees. I've been so exclusively focused on that gas valve/plastic gas & air mix chamber/plastic blower assembly that I didn't closely scrutinize other hidden possibilities.
    I've TRULY wanted to have someone else there to come and look at (and see) what I'm obviously NOT seeing, but my co-workers won't work on it because I took on the challenge, so they CHOOSE and PREFER to know NOTHING.

    Kinda puts a thorn in my side...if you know what I mean. With Rationals having a prominent presence in our kitchens, I'da thought someone else in the lot would step up, hit the books that I printed and tackle these beasts. Well...that's not how they think around here. They ride out their eight hours and go home.

    I know that, as it is, THAT'S not an option for field techs like yourself. But it should be (an option) here - IN-house. However, the general attitude within our occupation...to seek out and conquer it...and NOT have a callback on it... just doesn't exist here and these folks don't get.

    Anyway...I certainly SHOULD digress. I'm taking time off this week to rethink my position here as it is, so I guess I just vented some of that frustration. Thank you very much....

    I've seen perforated hoses you mentioned and had cut them back to better hose when I thought to do so.

    I DID take the burner out and looked for issues per the picture in the training manual. I remember taking one (THIS one I'm not so sure) to the shop to blow it out with air (from the outside IN). Today I read the book and it suggested running the burner through a dishwasher. Well HECK! Why didn't I do THAT?

    Gas pressure? HONESTLY...I checked it when the LOWER air blower melted down. But I can't remember if I did that during these three go-arounds with the TOP air burner. I mighta ASSumed it was fine since the other two burners haven't had issues.

    Sometimes ONE (being ME) must be reminded (by YOU) to get back to the basics that a service tech MUST check...EACH and EVERY service call. I guess my in-house practices have led to some complacency.
    ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° °

    "You never know what others don't know." -

    If I can't laugh at myself...then I'll laugh at YOU! -

  9. #8
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    > I'm taking time off this week to rethink my position here as it is

    Oh? Thinking of venturing out into the real world, are we?

    If I were you, I wouldn't hesitate dialing or emailing Claude, Pete, and the boys up in Illinois, or Klaus in Germany. It would be the thing I'd do from the site after verifying all the issues you've touched on, and I saw no obvious reasons for the shenanigans.

    Like we tell all the new techs, if you haven't got a handle on it in an hour or so, call someone- a senior tech, or the manufacturer, no sense beating yourself to death. Someone's been there, figured out something.

    I do, however, enjoy the occational "find", that I can share with the guys at the manufacturer. I once had a flat-top grill, LP, new, that would not burn clean; sooted up, yellow flames. Changing burner angle, moving gas valve right to left, nothing changed the flame. I by chance looked down a burner I had pulled out to clean, noted man, that's a long sheet metal screw they've used to hold the air shutter in place. Hell it's halfway into the venturi area. Substituted a real short one, and badda big, blue flames for ever. I had to wonder how many techs across the land struggled with that...

    Even if someone calls who has not been to the Rational school, just saying "Look, I've got 12 of your machines I take care of just fine, please help me out on this one stumper of a problem, will ya?" will get results.

    Mention how good the new Alto/Cleveland/Vulcan/etc combis are looking for good measure.

  10. #9
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    Well, it's out of my hands for a few months.

    That *company* came out. Looks like it's getting a once-over. New hoses, everything I'd replaced, a new upper air burner and...*cough*...a new upper heat exchanger.

    A good sale, I'd say. He owns it from here, so as long as it lasts longer than the standard 30 labor/90 parts warranty, I'd say that I've learned MY lesson.

    I r-e-a-l-l-y don't like these gas units.

    (Geez I shouldn't say that. We got seven of 'em)
    ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° °

    "You never know what others don't know." -

    If I can't laugh at myself...then I'll laugh at YOU! -

  11. #10
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    Entire gas train assembly as a kit may be cheaper than ordering parts individually. It should include all the gas train parts plus heat exchangers

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