RATIONAL oven has me IRRATIONAL

[ECtofix]

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?

[Protocol.]

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?

[ECtofix]

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.

[BadBozo2315]

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.

[BadBozo2315]

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.

[BadBozo2315]

I wonder if the gas pressure is dropping over time...

Things to check...

[ECtofix]

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.

[BadBozo2315]

> 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.

[ECtofix]

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)

[Protocol.]

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

[GT1980]

was there a prescribed air-temp differential, marginally acceptable?

close to BTUH= CFM x 1.09 xTempDiff(F)

CFM= BTUH/Td/1.09 to check CFM at spots

[BadBozo2315]

>was there a prescribed air-temp differential, marginally acceptable?

Looks like another lost soul..

In any event ECtofix, how did this all turn out? Did *that* company fix it, or should I have a word with the district manager?

[ECtofix]

Looks like another lost soul..

LOL! GT1980 is renowned here on H-Talk for his own forms of communication. My mind (and most others) is too simple to interpret it or conjure up an equally complex paragraph of techno-babble.

In any event ECtofix, how did this all turn out? Did *that* company fix it, or should I have a word with the district manager?

SHshshsh! Don't wake it up!

Probably too late now. Yes, yo...uh, I mean...*THAT* company did indeed resolve the issue. Thanks for asking!

[Olivero]

So, did they solve it by changing everything out in and around the area the problem was?

Geez, must have been expensive.

[ECtofix]

So, did they solve it by changing everything out in and around the area the problem was?

In addition to all other gas train components I'd replaced, that tech pointed out a possible crack in the heat exchanger. He showed me what he was seeing, but my feeble old eyes still truly never saw what he pointed at as a distinguishable problem.

Nonetheless, we went with that and let him replaced everything (again) in the gas train along with a new heat exchanger...and...it's been good for over a year now.

Geez, must have been expensive.

I don't get to see those rare bills, but MY ballpark estimate is 3k in parts alone.

As it stood though, my manager hired me for my field experience. I never, ever said to him that I'm the master of it ALL. So, when I'd conceded to advising that we get an outside service company to put some fresh eyes on it, there wasn't any hesitation. For that, I appreciated their faith in me and their confidence in my judgement.

When I was with that service company, there were occasions when I'd requested another tech to swing by when I was befuddled on a job. AND...there were occasions when I was asked to swing by to help another tech on a befuddling problem.

Now, we presently have seven guys in our shop (and our supervisor). But I'm the only one that came from a service company dedicated to our trade. I think I've taught these guys MUCH (especially on gas equipment), since their initial experience levels on kitchen equipment was gravely "muted" when I first arrived here. But in my five years here since then, I've noticed an overall improvement in how they approach the repairs (for reasons I won't elaborate on).

By the same token, I've learned MUCH from them. A few of them have committed to mastering repairs on mechanical aspects of equipment that I've put few wrenches to (lift systems on Sveba Dahlen rack ovens, our Werner and Pfleiderer mini-roll machine, etc.). These guys have really stepped up to...and into it...in their ability to keep stuff rolling.

So as one in-house guy to another, Olivero (although you weren't asking), I guess I'm just saying that there is no way that you can be the "be all to solve solve it all". You gotta rely on a great team of other techs to help out when necessary...and as long as you've earned your manager's confidence that you've done all you can, you should expect their door to be open for getting you some help.

[Olivero]

Glad they fixed it, I once snapped a bolt in a heat exchanger right off, scared the living crap out of me, thought I would have to replace it, then I remembered I could just weld it back on... lol.

Anyways, I think you got a good point, I end up being relied on to fix or build anything they want here, I can always call for help or get a service company but in most cases, I just end up figuring it out with the manufacturer.

But the manufacture's tech support guys are just like us, been in the field, done it before and know what's up or have an idea of what's up and if they don't try to figure it out with us.

Its unfortunate when people get trained a certain way and end up sticking to it when its a bad style, this "Oh that's got a problem? gotta get a new one" attitude is what bothers me the most.

[MauiTech]

Hmmm I have a similar situation now I got myself second guessing and feel there may be a crack In the heat exchanger... what’s weird is prev service company had installed a orange gas valve which indicates 120v and when I look up the part on rational portal it shows it to be a 220v gas valve same as is on the lower burner.

[ECtofix]

what’s weird is prev service company had installed a orange gas valve which indicates 120v and when I look up the part on rational portal it shows it to be a 220v gas valve same as is on the lower burner.

Hmm. That doesn't sound right.

I looked around on PartsTown and found two of those valves. Part numbers 70.00.374 and 70.00.375. Sure enough, 120v. Rational's parts price list shows those being intended for ovens in Canada's market.

Canada uses the same power that we in the U.S. do. Maybe they have different standards than we do and specify only 120v components in their gas ovens.

As you probably know (so I say this for those reading this who DON'T), Rational makes ovens (even gas-heated ones) to operate from European power (230v), but they incorporated a step-up transformer for ovens sold in the U.S. so we could run our ovens from 120v.

Does that oven you speak of have a big torroidal transformer in it?

If you already have a gas valve in it that's 230v, then all two (three in 202s) should be 230v, so that company put the wrong valve in it. I'd inform the customer about that right away, because they paid a pretty penny for that repair and that 120v valve won't last long!

[MauiTech]

Yes the steam gas valve is 230v black coil and bottom heat is 230v however I noticed top heat has a orange valve 120v, I was called out cus they get reset gas , sure enough it’s from top burner - found blower for burner not spinning and noticed this strange orange valve never before seen - turn it around and see it’s labeled 120v I then go on my rational portal to look up correct part number and it should be the 230v valve..... the prev company no longer services rationals, I’m just dumbfounded why they would put that in and how long did it last

[MauiTech]

120V Gas Valve by D C, on Flickr