Repairing an air fryer

[amateur_24]

Hi
I am trying to fix an air fryer that doesn't turn on.
I have discovered there isn't any ac power coming into the main board but there is ac power on the mains flex connection.

I traced backwards from where the ac is connected to the board. I found the board to be wired in series with a device shown in the picture. There are two one in series

What is this device called and how do I test it?
I suspect it's failed because that the only point of failure I can find.

 

[MaxHeadRoom78]

That is a thermal fuse, generally opens due to lack of fan working as one possible reason for over-heating.

 

[amateur_24]

Why did I measure mega ohms of resistance across it then? If it's a fuse should it not be 0 ohms?

 

[rjenkinsgb]

Why did I measure mega ohms of resistance across it then? If it's a fuse should it not be 0 ohms?

They are safety devices, once blown they are a permanent disconnection, rather than self-resetting.

It's blown.

 

[MaxHeadRoom78]

Why did I measure mega ohms of resistance across it then? If it's a fuse should it not be 0 ohms?

Yes, normally 0-Ohms
If meg-ohms then the fuse is open! There should be a size/value on it.

 

[amateur_24]

Does anyone have any idea why this air fryer has had both it's internal mains rated 3.15a and the thermal fuse blown.

I get the feeling something is very wrong with it.

I have already tested the heating element. The resistance reading is 31ohms. There is no short to earth.

 

[Nigel Goodwin]

Does anyone have any idea why this air fryer has had both it's internal mains rated 3.15a and the thermal fuse blown.

I get the feeling something is very wrong with it.

I have already tested the heating element. The resistance reading is 31ohms. There is no short to earth.

3.15A is too small to power an air fryer, and really too large to power just the electronics in an air fryer - so exactly where is it connected?, and has someone fitted the 3.15A fuse and it's not the correct value?.

As has already been said, the thermal fuse has probably blown due to over heating, has the fryer been keep clean and well ventilated?.

Heat fuses are a common failure where they are fitted, and sometimes fail for no reason.

 

[amateur_24]

The air fryer hasn't been worked on before me since we bought it new.

The thermal fuse was completely clean because the heating element has a metal shroud around it. The thermal fuse was mounted on the other side away from the heating element.

I don't have the original fuse any more. It doesn't look like the fuse is protecting the heating element.

Does anyone have any thoughts?

 

[MaxHeadRoom78]

The fuse could well be in the LV circuit that controls the element etc.
The board shows a couple of relays etc.
Remember, it does not necessarily open due to current, but (ambient) temperature.
They generally come with a generic rating of 15a, overall.
Obtain a couple of spares and see if the new one hangs-in!

 

[Nigel Goodwin]

The air fryer hasn't been worked on before me since we bought it new.

The thermal fuse was completely clean because the heating element has a metal shroud around it. The thermal fuse was mounted on the other side away from the heating element.

I don't have the original fuse any more. It doesn't look like the fuse is protecting the heating element.

Does anyone have any thoughts?

Fuses don't protect elements - fuses are there to protect external 'things', such as preventing the house burning down - it's not too much of a concern in the UK, as all plugs are fused anyway, and an air fryer will have a 13A fuse in the plug.

There seems no sign of any transformer?, so it's probably a crude (everything is live to mains) transformerless power supply, which 'could' be why it's got a 3.15A fuse in (it needs to be large because of the switch-on surge, yet will blow if the dropper capacitor goes S/C).

First off - get a suitable 3.15A fuse and replace it - then TEMPORARILY!!! short out the thermal fuse and see if all works OK. If everything is good, then you can buy a thermal fuse and replace it.

If you're wary about trying it with the thermal fuse shorted out?, then get a thermal fuse and replace that before testing as well - shorting the old one out first is just to save you killing a thermal fuse you've just spent money on.

 

[MaxHeadRoom78]

Here in Canada I can obtain spare thermal fuses for ~0.50c, $1.50 tops.

 

[rjenkinsgb]

It looks to have a single-chip high voltage switched mode PSU - the "8 pin" size IC on the underside with a gap in the pins is typical of some of those devices.

Possibly one of this series? Although they are mostly used to drive transformers, they can be used with just an inductor & smoothing etc.

https://www.farnell.com/datasheets/2237895.pdf

 

[amateur_24]

Yeah there's no transformer.

I tried shorting the thermal fuses and it switches on now. The fan appears to be working. I disconnected the heating element because there's no thermal protection.

Is it a good idea to have a thermal fuse on both line and neutral? I thought it was frowned upon.

I have ordered some thermal fuses off eBay. I do hope the heating element is ok. If it all works, what caused it to blow both thermal fuses and the 3.15a mains fuse?

 

[Nigel Goodwin]

Yeah there's no transformer.

I tried shorting the thermal fuses and it switches on now. The fan appears to be working. I disconnected the heating element because there's no thermal protection.

Is it a good idea to have a thermal fuse on both line and neutral? I thought it was frowned upon.

I have ordered some thermal fuses off eBay. I do hope the heating element is ok. If it all works, what caused it to blow both thermal fuses and the 3.15a mains fuse?

Why did you try it with the element disconnected? - the whole point was to see if it worked, and you didn't do that.

You only need thermal protection if you're actually using it, not just for testing it - and such thermal protection will take a considerable time to operate anyway.

As for thermal protection in both live and neutral, I don't see as it makes any difference? - and could just be a simple way of monitoring the temperature at two different points.

 

[MaxHeadRoom78]

Yeah, so what do you think is going to open a thermal fuse with the element disconnected ????

 

[Doug]

Don't solder in the new thermal fuse as the heat from soldering will open the new fuse.best to crimp it.
You can solder it if there is something on the thermo lead to reduce the heat as in needle nose pliers

 

[Nigel Goodwin]

Don't solder in the new thermal fuse as the heat from soldering will open the new fuse.best to crimp it.
You can solder it if there is something on the thermo lead to reduce the heat as in needle nose pliers

If you're blowing a thermal fuse by soldering it, then you need more practice at soldering properly (the end of the wire is a very long way from the actual fuse).

However, it's best to crimp them if you can.

 

[amateur_24]

Where can I get suitable crimps? All I can find on eBay is crimps they use in the electrical field.

I have soldered the connection for the heating element back in. I ran it for 10mins and it seems to be ok.

Thanks to everyone for your help.

 

[Tony Stewart]

They generally come with a generic rating of 15a, overall.

true for many but not for this 300W one I found that uses 3.12A fuse at 120V

https://www.amazon.ca/Maxi-Matic-EPM-250-Tabletop-Retro-Style-2-Ounce/dp/B002DUCCEM/ref=asc_df_B002DUCCEM/?tag=googleshopc0c-20&linkCode=df0&hvadid=292896339311&hvpos=&hvnetw=g&hvrand=12284596294177047181&hvpone=&hvptwo=&hvqmt=&hvdev=c&hvdvcmdl=&hvlocint=&hvlocphy=9000793&hvtargid=pla-385520496882&th=1

 

[MaxHeadRoom78]

Is that the thermal fuse?
That is what I was referring to, they are rated in temperature, not amperage, except the max rating.
Usually either 10a or 15a for kitchen appliance type.