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  • Combi Oven Uneven Cooking

     olivero updated 2 years, 1 month ago 1 Member · 31 Posts
  • guest

    Member
    March 23, 2018 at 12:00 am

    Well, lets add another one to the list of problems.

     

    Uneven cooking, they cooked about 600 lbs of roast beef or pork today and about half of it came out still pink and not cooked enough. they used the Convotherm 4 and the OGS 20.20 unit but it was mainly noticed on the OGS 20.20.

     

    I checked the suction panel in front of the fans, its locked in and tight. 

    I checked with the Chef on the other points Convotherm brings up and nothing seems to indicate as the problem.

     

    If there was a fan speed error on either fan or a ignition error, the oven would tell me so what is happening here?

     

    Apparently its not totally new, they’ve seen it with other foods but I guess this time it really showed. They can’t do cheesecake in them either as they don’t cook evenly.

     

    Any ideas?

  • fixbear - ADK NY

    Member
    March 23, 2018 at 12:38 pm

    Ah, a difficult one. Sorry you seem to get them. 

    Exactly where is is slow cooking?  Top, Bottom, left, right, Front back?  

     

    The monitoring system checks fan motor internal temp and speed,  But not the actual air flow. Build-up in a blade, Foil, blockage in the flow will cause problems with even cooking. As will something foreign on the racks disturbing the flow.  Convection ovens are fast, but they do rely  on proper and even flow to cook right.

  • olivero

    Member
    March 23, 2018 at 2:15 pm

    Lol, I should write a book.

     

    Its on the entire lower section of the rack, all the meat on it was undercooked and had to be recooked.

     

    They haven’t really changed anything, but something changed.

  • fixbear - ADK NY

    Member
    March 23, 2018 at 2:49 pm

    Lower burner or lower fan

    Do you have like a Fluke 52 temp unit. Place one probe high and one low.  Watch the delta

  • olivero

    Member
    March 23, 2018 at 4:58 pm

    No I don’t I was thinking that’s one way to tell. Put 2 different thermometers   or probes in there and see if they are any different.

  • ectofix - Nashville

    Member
    March 23, 2018 at 5:36 pm

    I’ve never addressed (or even heard of) that problem on a combi-oven of ANY size, since they usually (but not always) are designed to reverse blower direction in a cyclic manner.  Additionally, combi-oven blower wheels are far more substantial than the diminutive squirrel cage in standard convection ovens.  AND…(unlike standard convection ovens), I’ve never seen foil or debris get caught up in a combi-oven blower wheel – since the wheels vane spacing is wider.

     

    SO, a dumb question…since I don’t know if this even possible, but –  are the upper and lower blowers possibly turning opposite directions within a simultaneous cycle?  I’m pretty sure they should both be turning the same direction (within a cycle).

    I’m not sure if that matters, but just something I thought of.

     

    Is the door gasket sealing properly at the bottom…around the trolley?

     

    °     °     °     °     °     °

     

    I don’t know what else to think of…other than heat source malfunction.  Yet, if there were issues with the bottom heat exchanger burners, the oven controls would certainly inform you of that.

     

    I also considered the possibility of loading of the oven racks a different…or wrong way.  I can’t see that as being an issue, since the oven IS DESIGNED for accepting a trolley FULL of pans of product. 

    But on that note, I’ve never read the operator’s manual.  So, really don’t know of the stipulations on proper loading of that oven size.

     

    • Hmmm…  There’s a thought.  Additionally, I seriously doubt that the Chefs have read the manual either. 

     

    OH…one other thing:

     

    I’m not overly familiar with Convotherm’s (old or new).  Although I got factory training on the original ones a dozen years ago, I can only remember working on two during my next six years in the field.

     

    ANYWAY – my Rational ovens require a self-calibration cycle to be run whenever any major parts, controls or sensors are replaced.  The intent is to make the oven computer RE-LEARN & adapt to any changes between old and new components or operating environment. 

    – YES – even if the oven is MOVED, Rational says it should be recalibrated. 

    The self-calibration cycle is something a technician must set up properly and initiate by following instructions in the service manual.  A fully functional Rational takes forty-five minutes to complete that process. 

     

    So I was just wondering.  Do Convotherm maintenance procedures call for doing such a thing as well?

    If so, have you attempted to run the ovens through that?

  • fixbear - ADK NY

    Member
    March 23, 2018 at 6:03 pm

    Ectofix’s thoughts have triggered a idea.  Is it possible the the oven sensors have drifted so that the top is cooking faster than the bottom.?

  • olivero

    Member
    March 25, 2018 at 8:40 am

    To answer both questions,

     

    Ectofix

     

    SO, a dumb question…since I don’t know if this even possible, but –  are the upper and lower blowers possibly turning opposite directions within a simultaneous cycle?  I’m pretty sure they should both be turning the same direction (within a cycle).

    I’m not sure if that matters, but just something I thought of.”

     

    I guess its possible but I seriously doubt it, nor is there a good way to confirm it other than trying to see through the glass door and then through the suction panel.

     

    This unit leaks steam still, can’t seem to get a grip on it regardless of what I try, my last conclusion is that the trolley is not level due to the floor not being level. Offered to put spacers on the casters and make the racks specific for the 1st or the 2nd one but they didn’t want that. So leaky combi it is.

     

    The oven hasn’t particularly changed anything or had anything majorly changed, this is the good one whereas the convotherm 4 has pretty much had 30-40%  of its parts changed already.

     

    Convotherm has never mentioned a calibration type test, never seen it in the service, repair, install or user manual. 

    The chefs have read the manual, they can’t operate the equipment unless they have read them. 

     

    Fixbear,

     

    I had a similar concern but as far as I know, there is only one temperature measuring point in the cavity of the oven, sits a little but above the middle point of the oven, or it might be near the top, can’t remember. It also has a core probe which is another way to cook but from what I know, its measuring cavity temperature only by this 1 thermometer, That’s as far as I know.

  • fixbear - ADK NY

    Member
    March 25, 2018 at 1:19 pm

    You mentioned that the carts don’t seal.  Is it possible that the oven ventilation  blower system has changed.  If a closed system and house atmospheric pressure has changed, it could be sucking air in the bottom there by cooling that area.

    As I recall, the blower wheel is inside the heat exchanger and blows air 360 over it.  But how does it get ducted to the specific areas of the oven cavity?.  Do they use plates to portion the flow more to one area than another? 

     

    A smoke generator may be of some assistance here.

  • olivero

    Member
    March 25, 2018 at 4:07 pm

    Fixbear,

     

    I don’t know how it would have, its part of the core programming as far as I know, its not something the chef or myself could just go and change if we thought the lower fan should run faster. The unit has a vacuum relief on top of the oven so I doubt any suction is happening.

     

    The way these work is the heat exchanger kind of wraps around the fan wheel and blows air over it which is how the hot air moves. The suction plate that I mentioned earlier is what controls that “ducting” of the air.

     

    Cleveland C2216467 PLATE,GUIDE,AIR FLOW | Parts Town   that’s one of them, just mounted on the wall.

     

    Can’t find a picture of the fan guard /suction plate but here is the internals and everything in it from Convotherms Service Manual

     

    It looks like there is only the B6 which measures oven temperature, its placed higher though, right above the top HE’s fan wheel. Kind of an odd place I think.

     

    yeeeeeeah. smoker, they don’t offer that for this unit. We tried to figure that out.

  • ectofix - Nashville

    Member
    March 25, 2018 at 5:03 pm

    olivero wrote:

     

    It looks like there is only the B6 which measures oven temperature, its placed higher though, right above the top HE’s fan wheel. Kind of an odd place I think.

     

    That’s the standard place for a cavity temp probe.  Same with convection ovens.  Hottest spot in the oven is towards the top.

     

    Olivero,

    Any issues with the quench (condensate) solenoid valve?  I believe it cycles at something like 140° in the drain box.  If it’s stuck open, then it effectively could facilitate too much venting through the drain.  

    I’ll explain that theory if you need me to.

  • ectofix - Nashville

    Member
    March 25, 2018 at 5:05 pm

    Not a Rational.  Just one cabinet probe at about 10 to 11 o’clock from the upper elements (or heat exchanger).

     

    Read my edit above about the quench valve.

  • olivero

    Member
    March 25, 2018 at 5:06 pm

    True, no doubt about it. But I haven’t seen many convection ovens about 6 feet tall by some feet wide. 

     

    Would make sense to have 3, 1 in the bottom, 1 in the middle and the last one in the top, or at least 2 average them and your done. As far as i know, Rationale and Alto Shaam have more than one sensor in their cavity right?

     

    On the quench valve, I haven’t noticed any more water coming out the drain, I could watch a bit closer but I haven’t seen any.

  • olivero

    Member
    March 25, 2018 at 5:38 pm

    On the quench valve, I haven’t noticed any more water coming out the drain, I could watch a bit closer but I haven’t seen any.

     

    It’s not a new problem, apparently been like this for a while, if the chef puts the core probe at the very bottom of the oven, it doesn’t undercook anything, it overcooks part of the top.

  • bush

    Member
    March 26, 2018 at 10:20 am

    ohm both of the HSI for burners, i suspect lower burner ignitor is failing.  For preheat from cold oven, all may work well.  When oven is preheated and product loaded, there will be a call for heat, the upper burner may work fine, the lower may not light off on the first or second trial for ignition and much time passes.  By then the chamber has reached temp and the call for heat is no more.  does this sound likely?

  • olivero

    Member
    March 26, 2018 at 10:32 am

    I guess it’s possible. But even then, the circulation of the air in the oven would pretty much nullify that effect, supposedly at least, the bottom burner does not always ignite intentionally, seems like its based on demand. Kind of like multistage cooling systems, depending on load more compressors come on.

     

    It also attempts a relight pretty much instantly if it fails, maybe a 1-2 second lag between them but I do get where you are coming from.

     

    I ohmed out both igniters about 3 weeks ago or so, both were well within their range (I can’t remember the number) but at the time I was happy with them.

  • bush

    Member
    March 26, 2018 at 11:18 am

    Keep in mind, there is only one temp sensor.  There will never be a call for heat for just the top or for just the bottom heat exchanger.  As for the two blowers circulating heat equally from one working heat exchanger,  it simply can’t.

     

     

     

    Sent from my Verizon, Samsung Galaxy smartphone

  • olivero

    Member
    March 26, 2018 at 11:43 am

    True, I do seem to recall having watched the call for heat go through and it would only light the top burner, I never fully confirmed my theory but if the bottom burner doesn’t light for 2-3 minutes whereas the  top burner is lit, it would either error out or finally light the bottom but I doubt those couple of minutes would make a major difference in a cooking cycle.

     

    I would not expect the top heat exchanger to carry the load of both but in terms of the air circulating around and evenly heating, I doubt those minutes matter.

     

    If it were a radiating heat type system like a residential electric oven with heating elements and no fan, I could see if the lower element was dying out and the top was doing good, you would have a significant difference but with the turbulence and air movement, I am having a hard time understanding how the temperature could be so different unless the air circulation for some reason just wasn’t circulating properly or if the lower fan was running too slow or too fast in comparison to the top one.

     

    I believe they have speed measuring modules or functions so the unit can see how fast the fan is turning and adjust as much depending on how the oven is programmed.

     

    I do find it interesting that if the chef puts the core probe in the lowest pan,  it doesn’t go uncooked, its not like the unit can’t facilitate the heat needed, it just seems the distribution or evenlyness is the problem.

  • fixbear - ADK NY

    Member
    March 26, 2018 at 1:32 pm

    I’m referring to a smoke test unit to be able to see the air flow. 

  • olivero

    Member
    March 26, 2018 at 1:50 pm

    Ah, never heard of that before. How does that work?

  • fixbear - ADK NY

    Member
    March 26, 2018 at 2:04 pm

    I guess it’s possible. But even then, the circulation of the air in the oven would pretty much nullify that effect,

    I would not expect the top heat exchanger to carry the load of both but in terms of the air circulating around and evenly heating, I doubt those minutes matter.

    L contrair.  Each area will primarily circulate in it’s own zone with maybe 10 to 15 percent mixing  Are the ignition modules identical?  With that much delay, it will definitely affect cooking from top to bottom.  If the manufactorer did built in a delay, they would have delayed the top burner, not the bottom.  Heat rises.

     

    Hot surface or spark ignition?

  • olivero

    Member
    March 26, 2018 at 2:41 pm

    Interesting, fair enough.

     

    I figured the delay is not really intentional but more of a verification process, ensuring the top is lit before lighting the bottom. in most cases, they light within a minute of eachother. As soon as the *boom* is heard of the top one, the combustion blower starts running on the bottom one and the lighting sequence begins.

     

    The ignition modules are the same, the igniters are hot surface ignition.

  • fixbear - ADK NY

    Member
    March 26, 2018 at 3:57 pm

    With hot surface, age of igniter and voltage/resistance cause huge variations.  IF they are staging the ignition, it should be bottom then top..  But when I looked at the wiring, they were fed together. Therefore should lite very close together if correct.  I’ve never been a fan of hot surface. I’ve seen several of the same igniters within the same brand take a big difference in ignition time. It’s just plain hard to control Silicone carbide.

  • ryantruck9

    Member
    March 26, 2018 at 4:03 pm

    I believe Bush is on the right track.

    Had a similar experience with floor model

    there was a time when Cleveland’s HSI’s were crap (maybe still are?)

    due to constant problems on a unit under warranty I was instructed to increase the trials for ignition from 2 to 4 trials

    months later the customer had the exact same complain you have written.

    they also had pictures of the entire roll cart of food and you could see the difference.

    I could watch the unit after preheat light top burner fine but would take 3 or all 4 trials to get the bottom burner lit

     

    the trials for ignition are quite long with prepurge and HSI heat time so effectively the bottom was running well below temp.

    if as Bush says the top burner managed to satisfy the call for heat the food didn’t stand a chance

    the bottom could be 100-150F lower than the top and its no longer calling for heat

     

    is your unit set for 2 trials for ignition? that could be around  7 min to lock out

    if 3 or 4 trials we could be talking 13-15 min before an error is recorded assuming it didn’t already satisfy the call for heat.

     

    Let us know when your facility eventually replaces that machine, perhaps we all book some time off and take it to an empty field with a cooler and some guns

    (I’m Canadian so you guys bring the guns, i’ll bring the cooler)

  • olivero

    Member
    March 26, 2018 at 4:13 pm

    Okay, I’m sold. I’ll give it a shot and see, sounds like it could be it. Cleveland told me to raise the ignition attempts to 4 a long time ago as there was frequent ignition problems (just bad igniters).

     

    Im gonna go see if its on, might be able to get some ohm readings by the time you read this.

     

    In regards to the empty field idea, Sounds like a great plan, much better than the spot in the dumpster I had reserved for it.

     

    I’m Danish, so I’ll bring the oven.

  • ectofix - Nashville

    Member
    March 26, 2018 at 4:41 pm

    I hope that’s the problem…so we know you found the problem.

     

    While ya’ll were talking, I took a quick view of the service manual.  I would expect the oven would show some derivative of  E05.XX error code if the bottom burner wasn’t working.  However, being set for more trials before lockout, maybe INDEED the time before locking out got extended long enough to presumably cook a batch of food.

     

    By the way, I have the space to perch that oven up for some target practice.  Only one one gun, though.

  • olivero

    Member
    March 26, 2018 at 5:11 pm

    Right, that’s kind of what I was figuring, I think if you were to preheat the oven, for sure the bottom burner would have to fire, no way the top could do it alone before the bottom would error out. But making up for 10-20* I could see that, cook pork or meat 20* below what it needs and I believe pink meat is what you get in which case it would make sense

     

    Next chance I get, I’ll check. Does if the burner is hot or cold make a difference? I seem to remember seeing odd readings when its hot and normal ones when its cold (room temperature)

     

    Lol, sounds good.

     

    Edit

     

    I checked both just now, Bottom is 6.3 ohms, top is 4.2 ohms. Timed the ignition, they are 14 seconds apart and it lights on the first attempt.

  • ryantruck9

    Member
    March 26, 2018 at 5:47 pm

    It can make a difference for hot and cold burners on ignition. 

    And with a heavy load the oven was probably working hard to recover after initial loading.

    Perhaps a micro amp test during a heavy cook cycle if possible? 

    Superheated flame rod starts to drift off burner?

    Ignition module messing around?

    Test hot micro amps and swap top and bottom modules?

    If its an intermittent module the chefs might think they didn’t set the right time it all underdone

  • olivero

    Member
    March 27, 2018 at 8:30 am

    Haha, I could defnetley do all those.

     

    I spoke to one of the chefs this morning, she said its not just the OGS unit, its also the Convotherm 4.

     

    I had understood the OGS was doing it much worse but she said they are both as bad. 

     

    Might just be the way those ovens are.

  • fixbear - ADK NY

    Member
    March 27, 2018 at 8:54 am

    Are they baking open or covered?  The reason I ask is steam bleeding into combustion mix will effect ignition. and flame quality.  Is it possible that oven leakage is getting to the burner intake?  Again, you have mentioned door leakage,  but how about kitchen air turn over?  Combined all together they may become cumulative and effect the available O2 .

  • olivero

    Member
    March 27, 2018 at 9:10 am

    Open.

     

    The air intakes for the venturis come from the control panel, the steam tends to get pulled up and to the side as they are under hoods. The only time steam makes it under the oven is if there is no rack in the unit. It definetley doesn’t make it to the second combi. The make up air is also present, definetley not a problem.

     

    Good thought though. 

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