Fridge heating element life span ?

[Sproket]

Is there a life span on fridge elements ?

Last week the fridge was working ok on electric, when I opened the van up yesterday afternoon and switched everything back on it was working ok and the temperature was dropping steadily, but by 10pm it had started to get warmer inside hmy: hmy: so the perishables were taken out & put into the coolbox while this morning. Turned it back on again and heat was coming out of the top vent so it seemed a bit of a mystery as to what was happening so nipped to the supermarket and bought a bag of ice and that seemed to work, the fridge was getting cooler again so i put the bag of ice into the freezer for an hour or so...... then when i checked it again the ice was melting
looks like a job for the weekend to replace the element, it's now working on gas for the next few days. i suppose like most things there will be the type that last and the type that work for just a while ...

 

[Damian]

What model fridge?

 

[Sproket]

It's a Dometic RM4290L

I don't think that it will hve done more than 150 days at the most since the last one was fitted ....

 

[Damian]

The thing to check first , preferably is the current draw of the element with the use of a clamp meter. It should, if my memory is correct, draw about 2 amps.
If it is getting hot it may be the thermostat is faulty.

Next, if it is getting hot is check the cooling matrix at the back of the fridge.
At the top right hand side next to the burner chimney it should be VERY hot.
At the left hand end of the top coil opposite the chimney it should still be hot but not quite as much as next to.
Moving down the coils the heat should get less until at the bottom it is just warm.

If it is hot at the top right but not on the left, the cooling matrix is blocked.

Elements are a bit hit and miss on lifetime, some seem to go on for years, some hardly any time at all, in comparison.

I could never give a guarantee on life expectancy, they were too much of risk, but would as a gesture of goodwill replace a short lived element, just for my own peace of mind and good customer relations.

 

[Sproket]

We have two freez blocks for the cool bag and i put those into the freezer compartment earlier on when i switched over to gas only those have now frozen solid so could I presume that the matrix is working ok and not blocked ?

 

[Damian]

Yep, if it works on gas the matrix is fine.

 

[Sproket]

Well i have managed to get access to the top of the fridge & the thermostat...
Could i be right in thinking that it's the thermostat due to no difference in readings when the dial is switched round from 0 to 7 and it's only drawing a small amount of amp's

This is the reading that i am getting from the 240v element

This is the reading that i am getting from the 12v element

This is the reading that i am getting from the thermostat 0.0 in any direction ??

This is the reading when powered up it doesn't alter when the thermostat is moved either way

 

[ProfJohnL]

Hello Sproket,

The top picture shows a resistance of 324Ohms. This would correspond to the 230V element. This resistance would allow a current of 0.7 amps which corresponds to a wattage of 117Watts. As the element warms up its resistance will change a little so this looks spot on for the correct operation of the element.

The second picture showing 1.2Ohms again corresponds the normal resistance of the 12V element and would give a working power of 100W. Again this seems perfectly normal.

The third picture shows a resistance of 0.0 ohms or contacts closed. This is a little more difficult to diagnose. The thermostat is temperature dependant, and if the sensor is warmer than its top set limit, the stat will have its contacts closed to power the element to cool the fridge. Turning the control knob will only make it demand a lower temperature so the contact state will not change.

If you can run the fridge on gas, and then investigate the thermostat control you might get a different response. I you listen carefully you can usually hear the contact change when you turn the knob. When the control is demanding cooling, the contacts should be closed and give 0.0 Ohms and when its cool enough the contacts should open and give a No circuit reading.

The last picture shows 0.6A. This is the current running through the wire in the clamp. This is pretty close to the predicted current the element should take.

All these pictures point to a normally working 230V element. What it doesn't tell us is if there are any other electrical safety issues, for example a short to earth, which would normally cause the RCD to trip.

 

[Sproket]

Hello Prof...
Thanks for your words of wisdom .....
Thinking about the RCD that tripped the week before, a few hours after we had got all set up, when i re-set it, it did so strait away but we had no power in the van so i popped out to check the bollard and a few more people were out checking there's as-well, as they had all gone down, the site owner later told me that there had been a direct earth fault that shut everything down, so when the power was back on I checked everything and it all seemed ok the fridge was working, everything was working as should be, then the following weekend this happened, it just now seems to be too much of a coincidence as the RCD has not tripped when plugged into the mains at home ....

So back to it ....

I left the fridge on mains power last night and it had cooled down to - 4 hmy: on my multimeter and showing - 8 on a fridge thermometer, I have also re checked the element when it was warm the Ohms reading had increased to 350Ohms it was a tad higher but it was dropping all of the time when the power was off, the thermostat did click when turned to adjust the temperature but as it was already up at 7 i was not expecting it to allow power back to the element when turned down rather than up, have re tried this quite a few times and only once have i managed to turn it up from 3 and it clicked ( power was showing via the clamp meter ) and heard it click back off when turned back down to 1 ( confirmed it again with the clamp meter ) to get to the workings of this fridge is a rather long striping out job as the sink & hob have to be lifted and propped up to allow access, so I have decided to re-new both the element and the thermostat as i don't fancy having to remove it all again, if it does start playing up again in the future as the thermostat is the original one fitted when the van was new 15 years ago.

 

[Sproket]

Well for the fantastic sum of £72.16p a new element & thermostat arrived today

Everything now working as it should, the thermostat turns the power on and off as it should and it's only getting down to 0.c rather than - 8.c :huh: on an interesting point the new element measured more Ohms at 424 and only went up to 425 Ohms when hot, and only pulled just under 6amps ... so i Googled to find out how to do the calculation and the figures came out correct V x V / W
230v x 230v / 125w = 423 Ohms and if you divide the Watts into the Volts it will give you a figure of how many amps it will pull so 125w / 230v = 0.54amps

The old heating element was showing 324 Ohms and increased to 350 Ohms when hot, when i removed it and connected the meter up and twisted the wire around it was going all over the place rather than showing the same reading hmy: I suspect that the wiring has over heated due to the thermostat being faulty and that is what is showing up due to it breaking down ...

 

[ProfJohnL]

Hello Sproket,
The empirical process you described after my last posting, certainly suggested to me the problem was with the thermostat. It wasn't conclusive about the element, but with your latest readings on the new element it does point to some internal failure causing a partial short on the element winding. This could have led to hot spot on the element which disturbed the refrigerant cycle.

Its a bit of a chicken and egg debate as to whether the thermostat caused the element to fail or was it the other way round. or are the two failure just a coincidence. we will never know.

However It was wise to change both, and save your self the time and trouble of a second strip down.

Glad you have a working solution

 

[Sproket]

Seen as i have had the fridge out, I decided to fit a digital thermometer into the front panel of the fridge, so that should any more problems manifest it will be easy to tell what is not working, it will also be easier to tell that it's cool enough to put things in

I have fitted the stainless steel probe into the bottom of the aluminium fin's at the right hand side, with the cable using the same hole that the thermostat's use, most of these are powered by small batteries, this particular one is powered by the 12v system ( took a bit of finding ) the cable can be quite easily shortened

This is showing the temperature of 1.7C

These are the original thermostat end's ( left is 230v right one is for LPG )

This is the one for the digital readout

 

[xtrailman]

I would have contributed to this thread but I'm not usually on the forums when I'm away.
It made for interesting reading as my last caravan used 3 elements over 7 years of ownership. It got so I changed the last one through the outside vents, and used porcelain connectors on the original cable!

All three failed open circuit.

In contrast my present fridge is 4 years old on the same element.

 

[Gafferbill]

I am whispering this and probably tempting fate............but my caravan fridge elements both mains and 12volt are original and 20 years old.

The fridge performs well on all three power sources
I don't really understand why the elements fail unless they are now being made to lower specifications.

 

[Sproket]

Gaffer I think you have hit it on the nail as most things are now are built to a price, It's no good making them last like the old one's that last for ever like yours :silly: there's no profit to be made in them hmy:

I would have contributed to this thread but I'm not usually on the forums when I'm away.
It made for interesting reading as my last caravan used 3 elements over 7 years of ownership. It got so I changed the last one through the outside vents, and used porcelain connectors on the original cable!

All three failed open circuit.

In contrast my present fridge is 4 years old on the same element.

Unfortunately due to how the door front is attached it sit's the fridge back towards the side wall so that extra space to attempt changing the element in situ makes it impossible for me to get at ....

As it's all back together now you can't imagine was needed to be removed to extract this particular fridge due to everything being built in and around it.