Bypassing Fridge Thermostat

[brdb]

I currently ferment in a wine fridge which has a built-in thermostat which can range from 39F - 64F. I'd like to be able to chill below 39F, so I'm attempting to use an external temperature controller to bypass the built-in thermostat. I've attached a photo below of the built-in thermostat. In order to bypass it, would it be as simple as disconnecting the larger blue and red wires near the middle of the picture and then connecting them together? I'm assuming the brown wire is a ground for the circuit board, the smaller black and red wires in the top left are for the LED lights, and the black and white wires in the bottom right are for the temperature probe.

 

[mredge73]

That is the fanciest fridge thermostat that I have ever seen on here.
Without a schematic it is hard to tell what is what. I don't see the incoming/source power. You should have a hot and neutral coming into the box with the same gauge or bigger gauge wires than shown in the harness.

If not then it is likely a European device. Brown will be hot, Blue will be neutral, and Red will be the hot lead to the compressor.
You need to check these out with a meter to be sure.
With the fridge plugged in and compressor off you need to show power to ground on brown only.
With the fridge plugged in and compressor on you need to show power to ground on brown and red.
Only if both conditions are true, you jump brown to red.

 

[day_trippr]

If there is a condenser fan its operation needs to be taken into account.
At the least it wants to run with the compressor...

Cheers!

 

[mredge73]

Yep, being a wine fridge it may run the fan independently of the compressor.
Could be why the control circuit is so complex. This is something you will also have to investigate.

 

[brdb]

Appreciate the help guys, I was able to find a circuit diagram on the back of the unit. I'm no electrician nor do I have a meter to check what's hot and what's not. If you are able to tell what needs to be done from the below, I'd appreciate all the help I can get, otherwise, I'll leave it be until I can pick up a voltmeter.

Edit:
I also found this thread regarding bypassing the thermostat on a unit similar to mine using a PID controller with relay, however, I'm not really sure what exactly was done. For those with more of a background in electrical wiring, maybe you can put this into layman's terms for me?
https://www.homebrewtalk.com/showthread.php?t=346638

 

[mredge73]

I guessed correctly!
Jump Brown to Red and you are good to go.
Fan and compressor run at the same time.

 

[brdb]

I guessed correctly!
Jump Brown to Red and you are good to go.
Fan and compressor run at the same time.

Quick question, if I leave everything as is, jump brown to red, and plug the fridge into an external controller, will the internal temp read-out still work? or do I need to disconnect the brown/red from the internal controller then jump them? Thanks again for the help

 

[mredge73]

If you leave it as is and just jump those two wires together everything will appear to work as normal, it just will not be able to cycle off.
So yes lights and readout will work as normal and they don't have to be disconnected.

Rated current is only 2A so you don't even need a very big wire to jump them together, just make sure it is insulated so it cannot touch the chassis or blue wire.
Car stores like autozone also have splice connectors that you can use that bite into two wires without severing the current connection.
Note that this fridge was not designed to reach freezing temp so the fan may be a bit underpowered. If you find that your coils are freezing up after this hack, you may want to install a better fan.

 

[brdb]

If you leave it as is and just jump those two wires together everything will appear to work as normal, it just will not be able to cycle off.
So yes lights and readout will work as normal and they don't have to be disconnected.

Rated current is only 2A so you don't even need a very big wire to jump them together, just make sure it is insulated so it cannot touch the chassis or blue wire.
Car stores like autozone also have splice connectors that you can use that bite into two wires without severing the current connection.
Note that this fridge was not designed to reach freezing temp so the fan may be a bit underpowered. If you find that your coils are freezing up after this hack, you may want to install a better fan.

Yeah I was thinking a quick splice should do the trick. I'll keep the fan in mind if I notice frost forming on the back of the inside of the fridge (where the coils are). By looking at the circuit diagram/refrigerant type/etc is there any way to estimate how cool I can expect this to get without upgrading anything? If I can get to around 34F I'd be happy.

 

[sami1971]

I guessed correctly!
Jump Brown to Red and you are good to go.
Fan and compressor run at the same time.

Probably would be better to connect the brown to the external controller IN and then red to OUT.

Also I do recommend picking up a multimeter before doing anything.

 

[mredge73]

It isn't a frost free freezer so it will be able to cool until the coils completely frost over into a block of ice. Then it will blow air across ice so you will never get below freezing until you thaw it out.
A frost free freezer has a heating element and a powerful fan to keep this from happening.
But it will easily hold 34.

Odd that it includes a defrost sensor but no defrost heater. I bet it flashes a warning light or something.

 

[mredge73]

Probably would be better to connect the brown to the external controller IN and then red to OUT.

Also I do recommend picking up a multimeter before doing anything.

That would be better, that is how I wired up all of mine.
Basically makes the new controller a parallel switch to the old one, so if you remove the new controller the unit functions as normal.

Takes a little more work and some basic electrical skills.

 

[brdb]

I wound up using a quick splice connector to jump the brown and red cable and then I connected the fridge to an external temperature controller. So far, everything has worked as intended and the built-in lights/thermostat work as normal (except when the external controller cuts off power to the fridge). Thanks again for the help