Blown thermal fuse???

[monkey spanners]

Polar refrigeration prep counter.

Found a blown thermal fuse protecting a defrost heater, it was rated at 65c, do these just go with age?

Heater checked out ok. Have left it disconnected and raised the set point, hopefully it will keep going till i can get a replacement.

A friend in the trade says he just bypasses them, what do you think of this? seems a bit risky to me!

Jon :)

[sedgy]

hi jon, any chance of water getting through to the heater cables? water drys out heater now ok ? sedgy

[monkey spanners]

Hi Sedgy,

The heater seemed ok, it pulled about 1.9/2A (so i guess is around 500W), when i bypassed the blown fuse that is in series with it and melted all the ice the system then switched back to cooling ok.
The fuse was in a clear plastic bag, then in some of that heat proof braided sleeving and cable tied to one of the u bends on the evap. There were a few drops of water in the sealed bag with the fuse.
I think its only meant to blow if the controller sticks on defrost or something, just wondered if they wear out or age and then blow at too low a temperature, it was marked at 65C and i think the defrost terminates at 8C. the evap probe is about 2 inches away from where the fuse was fixed so can't see there being that much of a difference, and the probe is about three months old.

I know it needs a new thermal fuse, just wondered if anyone knew from experience that the heaters or something else is always duff too when the go.

[sedgy]

hi jon , sorry in my working experience we did not have fuses we had eather 4inch or 6inch nails , well I did say that I have been retiered a few years now all the best jon keep the job running, sedgy,

[Grizzly]

Jon.
Sometimes the what we may call "Old Wives Tales".
Are not so daft!
Based on my experience fuses can indeed get "tired" and blow.
Thermal fuses are no exception, indeed they could be said to blow more often than some.
The trade term for these is "One Shot" fuses.
Which says it all really!

Grizzly.

[coolhibby1875]

to answer your question, yes you should replace the fuse, if the timeclock, controller or contactor was to stick on defrost it could catch fire, i once got a call to a arneg cabinet once where the customer said it had gone on fire, what i had found was that someone had previously shorted the defrost klixon out, then the biggatti timer stuck on defrost and the result wasn't pretty, so in my book better always safe than sorry, more so than for the price of a fuse!

[paul_h]

Only experienced thermal fuses in domestics.
Yes they can blow for no reason, but also they can blow because the defrost cycle goes too long or never ends.
They don't blow because the heater doesn't work.

Bridge out the thermal fuse, run a defrost cycle, check that the defrost ends before the fridge catches fire (or 10C, whatever comes first).
If the defrost cycle finished when it should, replace thermal fuse and sign the job off.

easy to make you own fuses, they're about $1 ea from electronics places for a 70C fuse, small crimp union terminals and a length of heatshrink and you're done. Obviously a long length of heatshrink heated up no where near the fuse just to seal the ends and not blow the fuse. Use a lighter on the ends not a heat gun I used the thin clear heatshrink just so I could see the thing was sealed and the legs of the fuse hadn't twisted around and bridged the fusible part after I shoved it into place

[frank]

Hi Jon

I've had to replace thermal fuses in the past, most recently in the wife's hair straighteners :D

I would agree that they seem to fail with age.

Lots for sale on ebay, and if you scroll down the page a little you can see the new Samsung defrost thermal fuse http://shop.ebay.co.uk/?_from=R40&_trksid=p3907.m570.l1313&_nkw=thermal+fuse&_sacat=See-All-Categories

[monkey spanners]

Thanks for the replies, I'm hoping the replacements come already sealed in the water proofing, or i'll have to be very carfull with the heat shrink :D


Jon :)

[paul_h]

Yeah, they are already sealed, that's why you have to pay $20 and wait a day or more to get them then drive back to fit after already disassembling and and reassembling the fridge once already :D

I prefer to make my own up on the spot for ~$2 :D

[monkey spanners]

Well turns out they don't stock them as a spare part! So i'll have to make one anyway. Had a look on RS components and they do a reseting one that only resets after the power is turned off, so should cope with monkey style heat shrinking! Think i'll get a few just in case...

Jon :)