Member Since: 31 Aug 2010
Location: retford'ish
Posts: 2230
is multimeter reliable to test a thermocouple? Fridge issue
Hi,
had a Fridge Issue while at Remstone at the weekend, it would not work on gas, it would light with the prime button pressed in but when released it went out straight away
The Thermocouple was suspected
took the fridge out today, jet and housing cleaned, flue cleaned, both looked fine when removed
had a search on Froogle how to test the thermocouple and used a (good value!) digital Multimeter set on DC 200mV
red lead on the end of the TC and black lead on the copper outside, when probe end warmed with a lighter reading was hovering between 18.7 and 19.4
I took it that this meant the Thermocouple was good
refitted the fridge and exactly the same issue lights with a nice blue flame with the prime button pressed in but as soon as you release it the burner goes out, a caravan shop has suggested replace the TC anyway as the multimeter can not be relied on
£27 for a new one and £130 if its the thermostat valve if its that (thing its the only option left)
Any help and confirmation about the TC test please?
Any multimeter should have enough accuracy to check a thermocouples output"Never keep up with the Joneses. Drag'em down to your level. It's cheaper".
10th Jul 2017 11:26 pm
riverblanche
Member Since: 31 Aug 2010
Location: retford'ish
Posts: 2230
Hi,
thanks for the replies
Phoned a another dealer to order a Thermocouple, he was very helpful, but does not stock them and suggested an online supplier, he also asked if I had confirmed it was not the Micro switch in the control know for the power options, as that is quite common as well ! No whats that then?
So fridge back out and a bit more investigating, had it running and sometimes it did stay lit just not consistently so I could rule anything in or out
Only markings I could find on the TC are 07 42 spain so still no wiser although tested it again in-situ and get a steady dc22.5mV
Going to order a New TC as said ^ and keep fingers crossed
Any multimeter should have enough accuracy to check a thermocouples output
Interesting link to the Fluke site......one I've not seen before
I've got some K type t/c's I can check out then check the accuaracy with same t/c in a digital thermometer.
Just going back to your issue.....unless you know the exact type of t/c the "guessing game" can throw up some real daft values.
Checking with a lighter or "match" can get over 500 degCBREXIT - done properly.
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11th Jul 2017 9:00 pm
gstuart
Member Since: 21 Oct 2016
Location: kent
Posts: 14177
i may still have some old manuals laying around with some useful info that i can easily pass onto ur goodself
markings on ur T/c ref the 07 bit is normally the year of manufacturer
11th Jul 2017 9:17 pm
sputnixb51
Member Since: 23 Apr 2013
Location: Morayshire
Posts: 833
Don't forget the solenoid itself in all this, 99 times it's the TC once every now and again it's the solenoid, while the fridge is out just warm the TC with the solenoid pushed in it should set within 10 seconds and take between 15 to 30 secs to trip you will hear a click. If this isn't the case do it again with the new TC if it's good or better then your in businesss.
11th Jul 2017 9:44 pm
riverblanche
Member Since: 31 Aug 2010
Location: retford'ish
Posts: 2230
Hi,
thanks for the more info.
The stamping makes sense now it is from a 2008 Bailey so 07year 42nd week.
It is a Dometic RM8550 fridge
Sputnix is the solenoid in the gas valve, which you override/press in when you push in the prime button?
the treaded pin at the very bottom of this picture, the TC screws into the middle of the 3 brass sections above it, it has the white plug with 2 spade connectors on, this is where I put a bridge across to bypass the micro switch in the power control knob.
Last edited by riverblanche on 14th Jul 2017 8:39 pm. Edited 1 time in total
11th Jul 2017 10:21 pm
sputnixb51
Member Since: 23 Apr 2013
Location: Morayshire
Posts: 833
Yes that's it. You are pushing a light spring and valve plate off a seat to let the gas through the electricity generated by heating the TC strengthens the field in the solenoid coil around the valve and the magnet and holds the valve of its seat, until the heat is removed the magnetism dissipated allows the valve to slam shut. The terminals are to interrupt this action if you turn the control back to 12/240V the ignition also runs from the control . Also called FFD or FSD flame failure device, flame supervision device.
In
Gstuarts link 500 is the solenoid they call it the Magnet insert.
Last edited by sputnixb51 on 11th Jul 2017 11:02 pm. Edited 2 times in total
11th Jul 2017 10:36 pm
gstuart
Member Since: 21 Oct 2016
Location: kent
Posts: 14177
just came across this , in case u hadn't got a parts list for ur fridge
started to read through it , in case its got some useful info ,
11th Jul 2017 11:22 pm
gstuart
Member Since: 21 Oct 2016
Location: kent
Posts: 14177
sputnixb51 wrote:
Yes that's it. You are pushing a light spring and valve plate off a seat to let the gas through the electricity generated by heating the TC strengthens the field in the solenoid coil around the valve and the magnet and holds the valve of its seat, until the heat is removed the magnetism dissipated allows the valve to slam shut. The terminals are to interrupt this action if you turn the control back to 12/240V the ignition also runs from the control . Also called FFD or FSD flame failure device, flame supervision device.
In
Gstuarts link 500 is the solenoid they call it the Magnet insert.
hi
am trying to remember what the ohms reading should be across the solonoid , think they useto be around 50 ohms ????
been looking for the diagnostic service manual as that should say what all the readings should be , but alas i can't find it
fantastic write up by the way , when i was also a heating engineer it wasn't uncommon for apprentices not having any knowledge how the basic thermocouple worked
11th Jul 2017 11:38 pm
gstuart
Member Since: 21 Oct 2016
Location: kent
Posts: 14177
riverblanche wrote:
Hi,
thanks for the more info.
The stamping makes sense now it is from a 2008 Bailey so 07year 42nd week.
It is a Dometic RM8550 fridge
Sputnix is the solenoid in the gas valve, which you override/press in when you push in the prime button?
the treaded pin at the very bottom of this picture, the TC screws into the middle of the 3 brass sections above it, it has the white plug with 2 spade connectors on, this is where I put a bridge across to bypass the micro switch in the power control knob.
really hope this isnt being rude of me but have u got a carbon monoxide alarm
will go and sit in my corner
11th Jul 2017 11:56 pm
sputnixb51
Member Since: 23 Apr 2013
Location: Morayshire
Posts: 833
If the gas valve sets ok with a shorting link across the terminals in your photo, you can then suspect the interrupter circuit not having proper continuity somewhere and causing your not setting problem.
12th Jul 2017 1:07 pm
gstuart
Member Since: 21 Oct 2016
Location: kent
Posts: 14177
wondered if there's an interceptor flue stat on this
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lights with a nice blue flame with the prime button pressed in but as soon as you release it the burner goes out, a caravan shop has suggested replace the TC anyway as the multimeter can not be relied on 
No whats that then?
when i was also a heating engineer it wasn't uncommon for apprentices not having any knowledge how the basic thermocouple worked 
