Fridge And Freezer Forum

[tttonyyy]

Hello,

Had a problem with my fridge section getting warm, so I replaced the thermistors with ones bought from here but this didn't fix the problem (well, at least I have a spare set now!)

Eventually tracked the problem down to this device (top, middle) on the control PCB:

[img]http://www.cooldark.com/photos/temp/fridge_ptc1.jpg[/img]

It's marked PTC1.

It's in line with the fan and was getting hot and cutting out (I assume a thermal resettable fuse). Chances are it went faulty went the fan iced up a few months ago.

Anyway, all the markings are missing from it so I don't know what to replace it with. I'm hoping someone here has a circuit diagram for it and can tell me what part PTC1 is rated at.

For the time being I've replaced it with a 500mA quick blow fuse; the fan motor surges to about 230mA when starting and then runs at a steady 170mA.

Kind regards,

Tony

[Dave_Conway]

Unfortunately that information isn't available as Hotpoint will only show/replace the entire PCB (no component level repairs ).

But..... I do have an earlier PCB here with what appears to be the same PTC although there are no positions shown or any markings on the component.

If you want the PCB you can have it, PM me your address and I'll post it to you, just drop a donation to Children In Need to cover the postage

Dave.

[Guest]

That's very kind of you Dave, but given my old one was tricky to remove and came out in three pieces I think I'd be better off guessing the trip rating and fitting a brand new PTC. They seem a bit delicate.

[andy2]

Hi Tony

The device PTC1 is probably a thermistor (Positive Thermal co-efficient) these work opposite to the usual NTC (negative thermal co-efficient) thermistors like the ones that you replaced on the evaporator.

As the temperature of the PTC increases so does its resistance, thus limiting the current that flows to the fan. As they often exhibit a steep rise in resistance the current to the fan will be negligable above a certain temperature. If the current increases above normal (as in a stalled fan due to ice buildup) the PTC heats up and shuts down the fan.

Your PTC was probably faulty shutting down the fan too early.

This type of thermistor is used in place of compressor starter relays to shut down the current to the start coil after the initial surge has started the motor thus preventing the start coil from burning out.

Andy

[Tristan]

I'm currently diagnosing an intermittent issue with an FF92 where the fridge compartment sometimes maintains ambient temperature whilst the freezer is at its expected -22°C.

In investigating the problem and reviewing the various threads here I discovered Tony's question about PTC1 on the control PCB and, although his question was a long while ago, thought I'd record some useful information here for others that might need it.

Based on the current draw Tony reports I suspect it can be replaced with RS 198-848 PTC over-current thermistor,15R 234mA which has a trip current of 330mA and costs approximately £1.44.

[RickT]

Rs 198-848 is now discontinued and replaced with 191-1816

[Don-44]

Thanks to all for this post - Confirmed all the work I've done
Freezer at -22 Deg, Fridge at room temp
Replaced both the Green and Yellow thermistors in the back of the freezer to no affect.

Shorted out PTC1 and all's well (make sure you switch off before doing this, it's 240v)...ordered new part as above from RS.
By the way PTC1 is at the top of the board (if you just lift the panel up with wires still connected) next to the display PCB..mine was grey but not all are. It is marked on the board

Good check is to leave the fridge door open for 5 mins, then on closing, check the fan runs for a minute. (i.e. until the thermistor gets hot)

Thanks guys.