How To Test A Fridge Thermostat?

[Truman42]

Ive recently acquired a 210 litre fridge freezer where the fridge is cooled by a fan blowing air from the freezer section through a flap. It worked fine when it was in use at work.

Last week when it was hot in Melbourne I struggled to get my fridge down to 3C to cold condition a brew. I had to block off the fan outlets in the freezer so it would blow more cold air into the fridge section.

On Friday I put a keg into the fridge and left the freezer flap closed (I unblocked the vents in the freezer this time as the weather cooled down) and turned the fridge dial up to full. I went away for the weekend and when I got home tonight the fridge was at -2C. Luckily the beer in the keg was still okay.

I turned the freezer up to full and turned the fridge down to low and after a few hours checked it and the fridge was at 1C. The fridge doesn't seem to turn off unless it goes into defrost mode.

So Im suspecting it might be the thermostat. Is there a way you can check these using a multi meter? I can put an STC1000 on it in the meantime but preferred to use the fridges own thermo than have to buy another stc1000.

 

[pk.sax]

How about calibrating the fridge dial with a known thermometer? Easier?

 

[Truman42]

How about calibrating the fridge dial with a known thermometer? Easier?

Not sure what you mean PF. Even with the fridge turned down low and the freezer flap closed so minimal amount of cold air is let into the fridge cavity it still gets down to 1C. Surely it should cut out at around 6-8C.

 

[J.T]

Put both flaps about half way, turn the thermostat up to full and put your thermometer in. Once it gets to say 2c, wind the thermostat back until the compressor cuts out. The thermostats have pre determined differentials of about 4c, so it will cut in at about 6c. The liquid temp will average out to somewhere in the middle.

If you haven't already, put some containers of water in the freezer. This will keep the freezer section cooler while the compressor is off and it wont have to work as hard once it cuts in.

 

[Truman42]

Put both flaps about half way, turn the thermostat up to full and put your thermometer in. Once it gets to say 2c, wind the thermostat back until the compressor cuts out. The thermostats have pre determined differentials of about 4c, so it will cut in at about 6c. The liquid temp will average out to somewhere in the middle.

If you haven't already, put some containers of water in the freezer. This will keep the freezer section cooler while the compressor is off and it wont have to work as hard once it cuts in.

There is only one flap which controls cold air flow from the freezer into the fridge. The fridge dial is connected to the thermo which has its probe just next to the cold air coming out of the freezer flap.

I've tried turning the fridge dial back until the compressor cuts out but it doesn't. I have it set on its minimum now and the fridge temp is at 3C and the fridge is still running.

I will try the containers of water in the freezer as its currently empty. Thanks.

 

[Truman42]

I just checked it again and the fridge is down to 1C and still running. Then I turned the dial up a bit and back down to low but forced it slightly past low and it cut out. When I turn it back up to 3/4 it cuts back on again.
So has to be a fault with the thermo somehow. Just don't know how to fix it.

 

[bum]

Probably because you're not a fridgey.

Get a fridgey to look at it.

 

[katzke]

Easy fix if it works.

Unplug it and let it defrost for a day or 2.

Have read many times about this and even tried it once.

Seems like the flap or flaps get iced up and do not work correctly. Sometimes normal defrost does not do it. May even be the control that is iced up. The fridge side is not a regular thermostat, it only controls air flow from the freezer.

 

[Yob]

For the price of getting a fridge mechanic out, I'd be disabling the fridges thermometer and hooking it up to another stc, set, forget. And husband the ability to control more accurately

 

[Truman42]

Easy fix if it works.

Unplug it and let it defrost for a day or 2.

Have read many times about this and even tried it once.

Seems like the flap or flaps get iced up and do not work correctly. Sometimes normal defrost does not do it. May even be the control that is iced up. The fridge side is not a regular thermostat, it only controls air flow from the freezer.

Ive checked the flap its not getting iced up. And the fridge side does have a thermostat. The flap is connected to the freezer dial. You want the freezer to be colder you turn the dial up and it closes the flap. If you want the freezer warmer turn the dial and it diverts more air into the fridge instead by opening the flap. Probably not an exact means of controlling the freezer temp but I suppose it gives the freezer an extra -5C or so.

But the fridge has a thermostat and its sensor is next to the flap coming out of the freezer (But not directly under the aiflow.) As I said in a previous post if I force it past low slightly the compressor shuts down so obviously a dicky thermostat.

@Bum..No Im not a fridgey but good at basic repairs and would rather diagnose it myself than pay a fridgey to replace the thermo when I can repair it or replace it myself. More money for brewing.
I pulled out the thermo and checked it with a multimeter. On full I get 0 resistance which seems correct but set to off the meter doesnt show infinity like it should (Fully open circuit) which is why its not shutting off.
Will spray it with contact cleaner at work in case theres **** in there and if not I will replace it if they are cheap enough or use an STC1000 if they are too expensive.

Thanks for the help gents.

 

[Maheel]

whats the temp of the freezer part ?

i would buy two bags of ice and chuck em in the freezer if it's empty

my big arse fan cooled 410L loves to be full
i have a stack of forzen water bottles in the freezer and about 8 water bottles in the fridge area

seems to create a big frozen "cold sink" and the fridge is much happier on 35'c days

 

[Truman42]

whats the temp of the freezer part ?

i would buy two bags of ice and chuck em in the freezer if it's empty

my big arse fan cooled 410L loves to be full
i have a stack of forzen water bottles in the freezer and about 8 water bottles in the fridge area

seems to create a big frozen "cold sink" and the fridge is much happier on 35'c days

I never checked it but yes good idea I want to store some hops in the freezer but might also freeze some water for ice blocks and a few water bottles to fill it up as its currently empty.

I sprayed the thermostats mechanisim with contact cleaner and worked it through its full range and a lot of **** came out. Checked it with a multimeter and it now shows 0 resistance when set to max cold and infinity when set to min cold. (After freezing it for 30 mins)

So its all fixed and I saved myself $80 on a fridgie and another $80 on a new thermostat.

 

[stux]

Also, once you hook up the fridge/freezer to an STC the freezer will become useless.

 

[Truman42]

Also, once you hook up the fridge/freezer to an STC the freezer will become useless.

If I was using the fridge as a fermenting fridge set at 18-20C then yes I agree. It wouldnt run long enough to keep the freezer cold enough.

But if im using the fridge as a keg fidge at 4C then the freezer would still work fine and drop to -18C approx and would still be usable.

 

[stux]

If I was using the fridge as a fermenting fridge set at 18-20C then yes I agree. It wouldnt run long enough to keep the freezer cold enough.

But if im using the fridge as a keg fidge at 4C then the freezer would still work fine and drop to -18C approx and would still be usable.

Not so sure. The freezer would only run long enough to get the fridge cold, not long enough to freeze. Unless you controlled the fan/flap thing with the STC

 

[Truman42]

Not so sure. The freezer would only run long enough to get the fridge cold, not long enough to freeze. Unless you controlled the fan/flap thing with the STC

Yes but thats how the fridge works now.
With the thermostat set to hold the fridge at 4C it only runs long enough to get the fridge to this temp then cuts out. The majority of the cold air that is blown through the evaporator coil goes into the freezer secttion with only a small amount of cold air blowing into the fridge section. (Even more so if the freezer flap is turned up so it blocks all but a small amount of air from going into the fridge.)
Also because the freezer compartment is a lot smaller than the fridge it cools down quicker.
This is basically how most modern fridge freezer combos work. The thermostat is in the fridge section as it takes longer to cool it down as the freezer always gets the majority of cold air. If you turned your fridge thermo up to its highest setting, say 8-10C the freezer would still be cold enough to freeze. Although maybe only -10C instead of -18 -20C.
You cant control the flap with an STC either, its just a manual dial to open and close it and the fan must run when the fridge compressor is on or the evaoprator coils would just freeze over and do nothing.

The only time you would have a problem is running your fridge at 18-20C for fermenting. Your fridge might only kick in for 5 mins every few hours or so and then the freezer wouldnt be cold enough.

 

[J.T]

Yes but thats how the fridge works now.
With the thermostat set to hold the fridge at 4C it only runs long enough to get the fridge to this temp then cuts out. The majority of the cold air that is blown through the evaporator coil goes into the freezer secttion with only a small amount of cold air blowing into the fridge section. (Even more so if the freezer flap is turned up so it blocks all but a small amount of air from going into the fridge.)
Also because the freezer compartment is a lot smaller than the fridge it cools down quicker.
This is basically how most modern fridge freezer combos work. The thermostat is in the fridge section as it takes longer to cool it down as the freezer always gets the majority of cold air. If you turned your fridge thermo up to its highest setting, say 8-10C the freezer would still be cold enough to freeze. Although maybe only -10C instead of -18 -20C.
You cant control the flap with an STC either, its just a manual dial to open and close it and the fan must run when the fridge compressor is on or the evaoprator coils would just freeze over and do nothing.

The only time you would have a problem is running your fridge at 18-20C for fermenting. Your fridge might only kick in for 5 mins every few hours or so and then the freezer wouldnt be cold enough.

Correct!

I have it set on its minimum now and the fridge temp is at 3C and the fridge is still running.

Give it a tap with the handle of a screwdriver, that should help it cut out if its sticking. Then its time for a new thermostat.

 

[Maheel]

Also, once you hook up the fridge/freezer to an STC the freezer will become useless.

mines running on a STC and it happily keeps the freezer rock solid

IMO my fridge / freezer runs better on the STC

my hops and the kids ice creams are in there....