How Do Fridges Work?

[scott_penno]

OK. So I understand the basics of refrigeration, but over the last couple of weeks, it sounds like the compressor on my fridge (Kelvinator N400 ~10yrs old) has been on most/all the time. I thought that increasing or decreasing (warmer to cooler) the temperature on the thermostat just controlled the temperature at which the compressor turned on or off. Now, while the compressor on the fridge is constantly on, I can still control the temperature in the fridge by moving the dial from warmer to cooler or vice versa. This makes me think that the dial also controls the rate of flow of refrigerant as well - is this correct? The fridge is also capable of freezing the contents which makes me feel that it's not a problem associated with lack/loss of refrigerant.
Is my thermostat stuffed or is it something else?
Is this the kind of thing that can be sorted by someone who is moderately technically capable or should I just call an expert?

Any assistance appreciated.

sap.

 

[wynnum1]

If its on all the time either weather is very hot or needs to be fixed

 

[OLDS2006]

I got a freezer from Evil bay like that.
The thermostat had stop working.
My first fix was a cheap manual timer, which I later replaced with a fridemate.

 

[litre_o_cola]

OK. So I understand the basics of refrigeration, but over the last couple of weeks, it sounds like the compressor on my fridge (Kelvinator N400 ~10yrs old) has been on most/all the time. I thought that increasing or decreasing (warmer to cooler) the temperature on the thermostat just controlled the temperature at which the compressor turned on or off. Now, while the compressor on the fridge is constantly on, I can still control the temperature in the fridge by moving the dial from warmer to cooler or vice versa. This makes me think that the dial also controls the rate of flow of refrigerant as well - is this correct? The fridge is also capable of freezing the contents which makes me feel that it's not a problem associated with lack/loss of refrigerant.
Is my thermostat stuffed or is it something else?
Is this the kind of thing that can be sorted by someone who is moderately technically capable or should I just call an expert?

Any assistance appreciated.

sap.

The dial only controls the thermostat, basic rundown is compressor pushes liquid through small hole(orifice) liquid converts to gas momentarily creating cooling effect (no bias valve).
So if it freezes the shit out of everything it is just your thermostat.
My fridge did the same although it is 35 years old! I bridged the thermostat (removed) and now it just runs with a fridgemate.

 

[Bribie G]

If it's a fridge freezer and the freezer section in good and frozen, but the fridge is labouring, could need a regas. In my chequered history with fridges that's usually the first sign with an old fridge. If it's taken some time to get to that stage, a gas top up may keep you going for a while longer. However I'm not sure if the fridgies are still allowed to stock the old CFC.

 

[rich_lamb]

... and it sometimes helps to clean the condenser coils on the back, as dust builds up and reduces performance

 

[kelbygreen]

My fridge is doing this it seems the fridge part is not working well and the freezer is good. There is no coils on the back or underneath just like a compressor motor.

my bar fridge is the same it seems to go on alot more then needed but I found out the seal of the door is only touching 2mm of the fridge where it shuts and I loosened the door screws and tried to adjust it but it dropped back to original possition as the screws dont go all the way tight its stupid as I have had it about 6 months and it was only used once before for a weekend (as uncle had it sitting in the garage from new for a year) hence why I stole it from him lol

 

[Westoz]

Thermostats in older style cyclic defrost fridges can go out of calibration ie cycle longer /shorter than designed.
These type have a gas filled capillary tube( R11) and are a simple open /close operation by probe mounted on the evaporater (cold )pate
sensing temp change of evap . This in turn cycles the compressor on/off.
A lot of simple things like worn door seals poor door alignment will also effect the efficientcy of operation.

 

[kelbygreen]

the fridge I had has a button where the temp dial is that was fallen out not sure what it is I thought it was for the light but I put it back in and the door doesnt come anywhere near it so not sure what it is. Might be why it wont cool properly. As I say my freezer is fine just the fridge

 

[Westoz]

Jeez that is old . The button is for defrost commonly known as push button defrost.
These things are PITA do your self a favour and ditch it.
Also sounds like you may have a refrigerant problem or comp may be inefficient ie not pumping.
Look out for a good 2nd hand unit as yours sounds like its on its last legs.

 

[kelbygreen]

Yeah thanks. I am not sure if the button was pushed in or not maybe why its not cooling if its in defrost mode??? or will it automaticly come out of it. Its a fisher & paykel one it does cool ok to 18 deg but not sure if I want to try it for the lager beer which I wanted to brew tomorrow. maybe with rotating frozen PET bottles it might pull it off. damn fridges lol I will figure something out

 

[Westoz]

Yes they do pop back out if it didnt the fridge wont run at all. I would still be looking at another fridge.
Make sure you dont get the same type . red button in the middle of stat is p.b defrost.
Go for cyclic ,moist cold or frost free models.All fridge types make good brew fridges as do converted chest freezers.

 

[kelbygreen]

Yeah thanks. I am going to run the fridge without the fermenter in there to see if it cools as I only ran it when the temp prob was attached to the fermenter. a 23lt thermal mass would take alot of energy and time to cool from 32deg to 18 which It had to do the first time I used it. It may still be ok but without cycling it for its intended use I guess its hard to say

 

[barfridge]

Fridges are easy, all you need to know is that when a gas is compressed it heats up, and when it expands again it cools down by the same amount.

So the gas is pumped through the compressor, and it heats up, I'm not sure of the exact amount, but let's say it heats up by 50 degrees.
Then it flows still under pressure through the coils located on the back/underside of the fridge, and cools right down again, almost to the temperature where it started.
After that it goes into a chamber where the pressure is released, and cools down by the same amount it was heated up, so in my example it's 50 degrees.

So, as an example, let's say the air temperature is 30 degrees
gas out of the compressor = ambient + 50 = 80 degrees
gas at the end of the coil, once cooled = 35 degrees
gas in the evaporator chamber thingy = 35 degrees - 50 degrees = -15 degrees

I might be horribly wrong, but that's how it was explained to me

 

[kelbygreen]

I am not sure where the coils are on mine. they must be behind the metal on the back of the fridge as thats where the pipes go to. there is also a big hot patch on the back as well. Not sure how or if you can clean them I thought it would work better with them not covered. one pipe comming out is so hot cant touch and the other going in is cool to touch wouldnt say cold.

got the fridge to 4 deg but it took over 2 and a half hours is this normal with nothing in the fridge?? or is that a sure sign its on its way out

 

[litre_o_cola]

From what temp to start with?
If it is still getting cold but taking its time and being erratic then check the thermostat.

 

[Bandito]

... and it sometimes helps to clean the condenser coils on the back, as dust builds up and reduces performance

The manual of my food fridge says that there should be at leat a 10 cm air gap between the back of the fridge and the wall - this is to enable enough air flow which is created by convention. I am a big believer in this as I have often sent back beers for being warm. I have often been able to put this down to the back coils being too close to the wall - not tha they listened. I have been meaning to direct a computer fan at the back of my brew fridge to increase heat dissipation, but it would have to be on all the time as I have no way to switch 12V unless I add another relay to the temp controller to switch 12V.

The next thing is that the higher the room temperature the more the fridge will turn on. My brew fridge is brand new, but is a cheap $500 chinese model. When it was delivered, one guy lifted it up the stairs and said "I wish all fridges were this light". It does come on more frequently on hot days, and as I am sure all can attest, brew fridges do run for 50% or more of the time while cooling warm wort to temp - my temp controller comes on when the temp gets 1 degree outside the target temp.

Running often empty though...... sounds like a bad seal. The kegerator site on jp's site says that a piece of paper should be a bit hard to remove when jamed in the door (cant remember exact wording). I would think that if it were a leak in the cooling gas line which I am told is verry rare unless it has reciently been knocked around, that the freezer wouldnt freeze.

So check the seal I guess - visually, then using paper. An refridgeerant guy would find the cause, surely.

 

[kelbygreen]

From what temp to start with?
If it is still getting cold but taking its time and being erratic then check the thermostat.

it was about 23 deg. how do you check the thermostat???

 

[Ducatiboy stu]

I had a fridge that did exactly the same, the freezer froze well, but the fridge section didnt get cold.

The prob was a blockage in the fridge cooler coils, so it was a throw out job..

Modern fridges blow cold air from the freezer section to the fridge, so you only have 1 cooling coil to deal with, rather than 1 each for the fridge and freezer

 

[litre_o_cola]

it was about 23 deg. how do you check the thermostat???

Mine had the symptoms of not doing bugger all and taking forever to chill, then cycling hard and freezing everything.
You need to see if it is cycling the whole time when it is on when you are trying to chill something or just the light is coming on.
I tested mine by warming the probe up and seeing if it kicked in at any stages whilst adjusting the dial.