8 replies to this topic

[Sunlight Appliance]

Hello Everyone,

 

I have a client here in the Desert that is having intermittent heating problems with the upper oven. Thanksgiving was a "nightmare" for her in that the oven kept cooling down by itself. She said she set the oven to bake, but by the time it got to 300 degrees it would stop heating and eventually turn off. No fault codes displayed, just a nice return to the clock function. Bottom oven is fine.

 

I went out to diagnose the problem. I ohmed out the oven sensor at approximately 1100, the proper amount according to the techsheet located behind the control panel. I then ran both ovens at 350 and saw the upper one begin to stall and drop off. It read the proper temperature, but my infrared temp gun showed a decline there. No decline in lower oven. When I saw this I adjusted the temperature up to 400 on the keypad. At that point, the temp had fallen to 302 (according to the display) but DID start to work its way up when I made this change. At about 350 it started to stall out again and drop off, never making it to the 400 level. It never actually "turned off" for me, but my client said that in a few minutes it definitely would.

 

I do not have a complete model number or serial for you guys. The tag is there inside the lower oven, but the info has been worn down or rubbed off. If you know of another place the model number may be located I would be happy to look.

 

I just downloaded the service manual that Reg uploaded last month. I see how to access stored fault codes, however, it appears there is no self-test features on this particular unit.

 

Any ideas or recommendations? Thanks in advance.

[certified tech group 51]

Did you try a new oven sensor or at least swap sensors??..Could also be a faulty relay on the control board.....

[Samurai Appliance Repair Man]

Oven sensor part link ==> http://www.repaircli...23T10015/911009

 

[Sunlight Appliance]

Thank you both for your help. I have an appointment with her again in a couple of days. I will install the new sensor and then run it. With regard to the possibility of a faulty relay on the board, is there a way to confirm that?

[Samurai Appliance Repair Man]

With regard to the possibility of a faulty relay on the board, is there a way to confirm that?

 

Locate the bake relay on the ERC and run the oven while monitoring the the voltage on the output terminal of the bake relay (120vac).  If the voltage cuts out early, then either the relay is bad or the control voltage to the relay coil (usually 24vdc) is being cut off early.  If the latter, then this could be a fault in the board logic or the board could be responding to an incorrect signal from the sensor.  

 

A common way those sensors fail is called non-linear response.  That's where it no longer changes resistance in linear response to temperature according to the temperature-resistance chart.  So it could measure proper resistance at 70F (1080 ohms) but at 200F, the resistance may increase to 2679 ohms instead of the specified 1350 ohms.  That additional resistance would make the ERC think the oven cell is hotter than it actually is.  

 

Moral of the story:  Never assume a sensor is good just because its resistance checks good at room temperature.  You need at least two data points to assess a sensor.   

 

BTW, you should be using a a thermocouple instrument, like the Fluke T52, to measure cell temperature.  Using an infrared gun is inaccurate because you can only measure surface temperature, not air temperature and the emissivity of the surface cannot be accurately assessed to calibrate the reading.  And you have to keep opening the door, which dumps heat.  Infrared guns are good for other applications but troubleshooting ovens is not one of them.  

[Sunlight Appliance]

This is such great stuff! Thanks. I'll post back the results.

[certified tech group 51]

Generic rule is to let the oven go thru 7 on/off cycles, then use the digital thermometer and take the high and low readings....................I write the high temp down when I hear the relay opens ( and a glance at  the time )......and I write the temp. down when I hear the relay closes.       ( and a glance at the time ).......Do this about 6 times will give you the average temp. inside the oven.....................I have had customers tell me " The last guy that was here used a laser thingy but the temps still are not correct  ".........Ya gotta let the oven 'soak',  the walls, door, door glass, racks,  all need to get hot......  I know it takes time, the laser thingy is fast but not always correct....Great for measuring items that have been operating for a while, engine blocks, steam pipes,  hydraulic tanks...... Plus  the item needs to be dark, try taking a distance reading on a white item.......................

[Sunlight Appliance]

Thank you, sir, for this recommendation. It's one more tool I've got now. I appreciate it.

[Sunlight Appliance]

Okay!

 

Finally she was able to meet with me to finish this job. Ended up installing the new temp. sensor and that did the trick! Did not need to go any further with the control board diagnosis, although I was ready to.

 

I bought you guys a 6-pack as a way of saying "thanks." I appreciate your help.