thermocouple on chescold f40 fridge freezer

Thanks Mike
I am measuring with a dick smith multimeter. This thermocouple is made with the insulated positive wire running through the middle of a copper tube with the copper tube acting as the earth. According to web info this type typically output 14 - 30 millivolts). I place the probes of the meter on the tip of the thermocouple (+) which makes physical contact with the electromagnet in the gas safety valve and earth to the copper tube itself. I have experimented by repositioning the probe in the flame to a slightly different position and am now achieving 16.9 - 17 millivolts. I am using the 200m setting on the meter and have tried several positions, pressures etc and am getting a very consistent reading. Since moving the probe and obtaining a better voltage I now find the electromagnet is now much happier to seat. I would like to have a little more voltage but will probably be happy with the result as is. The thermostat is working with the gas flame reducing to 'pilot' at 0.2 C. The pilot flame is quite small so I am now worried about it blowing out while in the pilot position. Do you know if this can be increased (slightly would do). I notice a small screw on the side of the thermostat and wonder if it may adjust the pilot).I also note that the later models ie the f400 have less slots at the rear of the unit near where the flame is located and am wondering if fitting a plate at the rear to reduce ventilation (around the flame only) would help in avoiding the pilot blowing out. Comments would be welcome.
regards Kc

Hi Kc

Sound like it is a single thermocouple and, without digging out my tables of thermocouple voltages, 17mV sounds in the right ball park; however the Chescold fridges don't run a "Pilot light" as such, I believe the thermocouple is purely for safety purposes in case the flame blows out. Temperature control is achieved by varying the intensity of the flame manually with the control knob - afaik?

>The thermostat is working with the gas flame reducing to
>'pilot' at 0.2 C.

I don't understand the above?

My aged Finch 3 way is missing the protection plate around the burner but I rarely have problems with the flame blowing out, on very windy days I place something in front of the burner to protect it. I'll be interested to see how my new "blue" Chescold fairs in similar conditions.

Garth: don't forget cold junction compensation when measuring with thermocouples.

Mike Harding

Thanks Mike for your help. The flame is at full blaze while the unit is cooling to the required setting, in this case with the knob at 9 oclock, the temp reaches approximately 0.2 Celcius. At this stage the thermostat which according to the manual controls gas and 240v (not 12v) cuts in/out and the flame is reduced in size. When the temp rises a few degrees the thermostat then kicks in again and the flame goes back to full size untill the temp reaches 0.2C again and the flame reduces to a "pilot" flame. It then continues on this cycle.

I have yesterday bought a Chescold F400 (Green plastic case) in really good condition from neighbours so will use this while tinkering with the older f40, time permitting.

Thanks Garth

You have raised a good point, if the tip of the tc is not in the blue part of the pilot flame there may be insufficient voltage to keep the safety valve open. What I may have witnessed was not the pilot flame being blown out by the wind but the safety valve cutting the gas supply due to lack of voltage. As you said I will have to experiment more with the positioning of the tc. I will start there and see how i go. Maybe the size of the pilot flame is not a problem at all!!

regards kc