lincoln 3255 heats to 480-500 degrees for a day then the control board reads 70 degrees and burns everything

[olivero]

The board shouldn’t be reading anything, I would assume its your thermocouple or thermometer or whatever temperature measuring device is in the unit. 

 

In this case, that should be replaced. I have seen it with fridges, tends to explode glass bottles when the thermometer reads incorrectly and the fridge turns into a freezer…

[fixbear]

Check your control cooling fan.

Ohm out your Thermistor.

Verify correct voltage tap on temp control board for incoming voltage.

[ectofix]

WOW!  I looked at the Installation, Operation and Maintenance Manual.  That oven is nearly 8′ long.  I’ve never seen a Lincoln that big.

 

FWIW: Years ago, Lincoln and Middleby-Marshall shared the rights to impinger oven technology through an agreement stating that Lincoln could manufacture smaller models (counter-top and up to a certain size floor model) and Middleby could make all their models in the larger category.  I wonder if that agreement has since expired?

 

Anyway, Lincoln has primarily used thermocouples as temperature probes.  However, they HAVE had models that used RTDs (or thermistors.  I can’t remember which).

 

The OP’s problem is intermittent.  So, it could be a failing temperature probe, a failing temperature controller…or simply a loose temperature probe connection that arbitrarily makes or looses its connection under certain conditions

 

I’d check the temp probe connections to the temperature control board first to make sure they’re clean and tight..

 

fixbear mentioned checking the cooling fan?  Well, a failed cooling fan would certainly mess with the electronics.  However, Lincoln commonly incorporates some sort of sensing device (i.e., sail switches or control compartment high limits) to prove that there’s adequate control compartment ventilation and to prevent operation altogether if that ventilation is lacking.

[burtonmac]

Thanks.  I will check these out first.  Lincoln tech says could be clogged air baffles or air flow problem.  

[burtonmac]

Ok.  Will do.  Thanks.

[fixbear]

Didn’t Lincoln use a Klizon in the compartment for that that self reset?  Usually mounted near the air switch on the 1300’s

[ectofix]

fixbear, yes…and then some.

 

Lincoln was always changing their control circuit design to address the various challenges in keeping their ovens from requiring repairs.  Their ovens were nearly an experiment that was marketed and sold too soon, so constant changes were required to address their shortcomings.

 

Heck, just look at any service manual of their older model series ovens.  Those manuals are wrought with pages and pages of different schematics…to cover serial number ### and below, from serial number ### to ####, or from serial number ### and above.  The ovens were CONSTANTLY changing. 

 

SO…just within the realms of providing ventilation for protecting the control compartment components:

 

Some cooling fans were always on once the main switch initiated a time delay to run the cooling fan.  The time delay turned on the cooling fan right away.  However, the time delay was wired so the cooling fan ran for awhile (20 minutes maybe?) after the main switch was opened.  A control box high-limit (Klixon) would disable the oven if it got too hot.

 

In some cases, a sail switch in the control compartment would provide proof of adequate ventilation instead of using a normally closed high limit.  If the sail switch didn’t close, then the oven wouldn’t work.  The sail switches were problematic, since they were delicate and any crusty greasy buildup on them would prevent their function.  Hence, a down oven requiring repairs.

 

And…still ANOTHER variation is where a Klixon cycles the cooling fan on at 120°F and off at 100°F.  In the schematic for an old Impinger 1000 that I just looked at, there was (initially) NO control compartment high limit.  In later 1000 series units, that particular Klixon was eliminated entirely, the cooling fan was hardwired to the main switch and a normally-closed high-limit Klixon monitored control compartment temp to disable the oven if it opened.

 

Some oven designs included keeping the main blower running for twenty minutes after shutdown in order to assist in a cool-down.  Yet, some ovens WEREN’T designed to do that.

 

These are just a few examples that I noted by looking through some schematics these past few minutes.  I’m sure there are other variations.

FWIW, their conveyor system design also went through growing pains.

 

As for the oven that burtonmac was asking about here in this post, I can’t say.  It appears to be a newer model oven and Lincoln hasn’t made the service manual readily available for us to look at.

[fixbear]

I noticed that as well.  They do provide the service manual for the dash 2.  Not sure how close it is,  but any oven that you have to bend plates to adjust heat from frount to back makes me a skeptic.

 

   As for thermocouples, they are usually very reliable.   Especially compared to Thermistors.  Only problem is that the wires have to be of a alloy that is very brittle,  and tends to break with vibration.  And they can’t take overheat for extended times like high pilots’.  Thermistors have great reliability below 200 F,  but like any semiconductor degrade fast above that. They are usually a carbon molecule in a compound that varies densities with temp change there by changing resistance. Obviously making a non conductive compound the moves with just a degree  of temp difference enough to make the carbon powder more or less conductive is the real challenge.. 

[ectofix]

The type of probes used in cooking equipment is pretty much a mix, based on what works best for the equipment manufacturer’s design.  It’s difficult to generalize thermocouples, RTDs or thermistors, because there are numerous classes of each, so any one of the three can have some application in cooking equipment.

 

For instance, within the operating range of a convection oven, our Rational combi-ovens use a type K thermocouple. Our Vulcan convection ovens use a type J thermocouple (computerized temp control) or a thermistor (solid-state temp control).  The Blodgett ovens WE have all use a 100kΩ thermistor.

 

Can’t find RTDs being used in any of the ovens we have presently, but our PerfectFry fryer uses a RTD.  So does one of our Montague griddles.  Those each might operate at a slightly lower temperature range than an oven.  Yet, from some notes I have from studying on electronic temp controls years ago, RTDs have greater accuracy than thermocouples and are useful over a larger temperature range.

 

AHHH.  Whatever…

Leave it to the engineers to figure all that out.  I (WE) just need to have some understanding of how each type of probe works in order to recognize if they’re performing properly.

[fixbear]

RTD’s  (resistance thermometer) are just a thermistor that cost a lot to make and are very sensitive. Made by wrapping a platinum wire (or a copper nickle alloy of platinum)  around a glass or ceramic core. They are super delicate unless jacket is well designed, but then defeats the accuracy and speed.  They also work well to  1100 degrees.  I can see why they would want to use them in a oven with proper protection. They don’t drift.

 

Type K thermocouples are the workhorse for us and industrial measurement. They are a joint of chromel and aluminel alloys, have a range from -330 to 2460 F .  The big problem is once they get above 365,  they suffer green rot and change. Unless encased.  Learned that one the hard way. Also early ones the metallurgy wasn’t as good as today and they vary a lot.  You can test for this with a magnet. Should be non magnetic unless it has reached the Currie point of the fuse.

 

Type J is the old original we had in the fifties.  Made with iron and constantan wires, they work from minus 40 to 1380 F.  Best thing is they don’t degrade from heat till they reach 1380 Curie point