Repairing tumble dryer: what is this part?

[Dhillon]

Hi All,
Trying to work out what is wrong with my tumble dryer. This part sits in the vent duct so I think it maybe some sort of thermal cutout device but I have no idea how to test it? It has four pins but only three are used by means of one pink and two black wires:


I know how to test a two pin thermostat but the above part I have no idea about, there seems to be continuity across all pins.

Thanks
Dhillon

 

[KTW]

Looks like a Thermostat Bimetal Disc Temperature Switch.
What's wrong with the dryer?

 

[Dhillon]

Dryer operates as normal, drum turns but the heating element is not heating. I have continuity on the heating element, also have continuity on the two thermostats beside the heating element (120° and 140°). I have taken the two thermostats out and bridged across them directly to the heating element, still no heat.

So I took it further apart and found the above in the duct but don't know how to test it. Thought it maybe some sort of use once thermal fuse that had blown.

 

[Minder]

There is often a over temp thermostat used in case the others fail, the temp should be marked on it, they normally test as N.C. switch.
Usually you can get a parts list off the internet from parts suppliers by entering make/model.
M.

 

[Dhillon]

Hi Minder, Its a very old model Zanussi TD160. I have seen parts diagrams for the two thermostats 120° and 140° but nothing for this part. I think its part 3A in this schematic:

http://www.partmaster.co.uk/tumble-...7151&model_ref=336319&illustration_ref=328339

 

[Minder]

Not really obvious, you need the wiring diag, often it is printed on the back cover.
M.

 

[Minder]

It is labeled as a thermostat here.
http://www.ransomspares.co.uk/diagram/zanussi/tumble-dryers/46429/td160 (91676000900)/
M.

 

[Dhillon]

Yes your right. If I knew how to bypass it I could try prove its faulty. It has two black wires and one pink wire going to it, not sure which ones I need to bridge in order to bypass it.

 

[Alec_t]

Looks like a thermal fuse.
If you are getting ~ zero resistance continuity between all 3 wires then the device is probably ok.
Is the pink wire thinner than the two black ones (if so perhaps it is used to sense fuse tripped)?

 

[KTW]

I would start by looking to see where the voltage stops.
A common fault is burnt wiring near the heating element, the wire may be intact but the braid is damaged under the insulation.

 

[Dhillon]

Ok all some good news! I have put it partly back together just to see if anything has made a difference and we have heat again :0)

When I removed the thermostat from the duct it did have a build up of fluff on it, perhaps that was causing it to overheat? But I think maybe something had come loose and taking things apart and back together has helped.

Will put it all back together and see if it still runs.

Thanks for all you help.

 

[Robert Hill]

Hi, i've found this book quite helpful:https://www.amazon.co.uk/Washerdrie...468960955&sr=8-1&keywords=haynes+tumble+dryer

Only a few quid and may help with diagnosing the issue

 

[Dhillon]

An update and seeking some more advice. I received the replacement part but it only has two terminals whereas the original had three wires going to it (black, black and pink). I called the spares company and they said it was the right part (54 degree stat) and they could see a bulletin by the manufacturer saying the part had been updated. Unfortunately there was no further information available on fitting.

I am tempted to join the two black wires together and fit the new stat. The machine is very old so if it blows then no loss. Any other suggestions?

Dhillon

 

[Minder]

It is possible it was double throw, IOW had a common and N.C. & N.O.
What does it indicate with a meter?
If it has a N.O. it could be used for alarm etc.
M.

 

[Dhillon]

Hi Minder,
I have a meter and can report back to you if you guide me on whats required.

Cheers
Dhillon

 

[Minder]

Check continuity (open's closed) between all three terminals.
M.

 

[Dhillon]

Hi Minder,
There are four terminals, only the first three are used. There is only continuity between these terminals:

1+2 yes
3+4 yes

I am quite sure when I first tested this there was continuity between all terminals. When refitted the dryer worked for a few minutes and then stopped heating again.

Dhillon

 

[Sunnysky]

I am trying to imagine a 50yr old female climbing inside the dryer to replace the OTP switch in the customer review
http://shop.zanussi.co.uk/product/1258406014/Tumble+Dryer+Thermostat





I guess some units may have been 2 phase or twice the voltage so they had the option for DPDT break contacts. now I guess only low voltage with line 1 only.. or maybe fault indicate with two terminals on output?

Is your duct plugged up?

 

[Dhillon]

Mehhhh! The repair man on the phone must have had a wicked sense of humour.

 

[Minder]

Hi Minder,
There are four terminals, only the first three are used. There is only continuity between these terminals:

1+2 yes
3+4 yes

I am quite sure when I first tested this there was continuity between all terminals. When refitted the dryer worked for a few minutes and then stopped heating again.

Dhillon

Unfortunately with out a definite test we do not know what happens when it operates on overheat, but with only three terminals used, Just two of the wires should work as the supplier mentions.
Unless you do a little tracing or reverse engineering it would be a question of trial and error to see which pair allows the dryer to operate.
@Sunnysky (UK is 1ph 230v)
M.