Any refrigeration experts out there?

[disney7]

Just curious, as this is my garage beer fridge. It is a Danby DAR440, which I know a lot of people use as kegerators.

Anyway, it died. The inside smelled like a burned up transformer and it would not cool at all (compressor didn't even try to come on).

I took it apart and it looks like the mechanical thermostat died. No idea why.

The thermostat has a capillary tube running off it and just has a ground and two other connections. It shorts the two connections and that is what turns the compressor on. I shorted these wires and the compressor runs like a charm and cools the fridge.

Now for my question. Danby wants $65 plus shipping for this simple part on a $150 fridge. I have a spare $17 STC-1000 temp controller laying around and my plan was to wire it up as a replacement thermostat.

So here is my issue. The bulb end of the capillary tube runs to the back of the fridge, behind the cooling panel (big panel that gets cold, this fridge doesn't have a fan in it) and is attached to the back of the cooling panel. So, it would be reading a temperature WAY cooler than the ambient air in the fridge. I'm wondering if it is some sort of device to prevent the refrigerant from freezing in the lines and the actual ambient fridge temp is controlled by something completely internal to the thermostat.

Anyone know?

 

[jCOSbrew]

I use an STC 1000 to control my mini fridge kegerator, this is pretty common. I put the temp sensor in a bottle of water so it is more stable than ambient air temp resulting in less compressor cycles. There should also be a setting for the minimum compressor cycle time. It will work much better than the mechanical thermostat that came with the fridge.

 

[disney7]

Yes, I'm just wondering if eliminating the factory thermostat completely will have any unforeseen consequences.

 

[Dan]

I'm no expert but I don't see why eliminating it would cause any problems. The thermostat isn't really doing anything with a controller connected, never reaches freezing so it's always closed and sending power to the compressor when the temp controller powers on. I'd just bypass the thermostat and put your temp sensor in water like jCOSbrew recommends.

 

[disney7]

I just took the thermostat apart. There isn't anything extra in it. Just a simple single thermostat. I don't see why it quit working and smelled funny either though. I'll hook the STC-1000 up and let it run while I'm around.

Thanks

 

[SeeMont]

I was looking on this site, couldn't find it but there was a thread about doing just what you are wanting to do. I am using 2 - STC-1000 controllers with the temp prob in liquid, have been working great for about a year.

 

[mblanks2]

The thermostatic control that you have on the frig sounds as if is the type that contains a small amount of the same refrigerant used in the refrigerant circuit in it's capillary tube. They work by the heating and cooling which raises and lowers the pressure of the internal refrigerant. This in turn is tied into a switch that is activated by this pressure differential and the dial or setting that is used to set the temperature/number is calibrated to this particular design.
You should be able to replace it with your stc-1000 and measure the ambient air temperature for control of the frig with out any issues.

 

[estricklin]

This should work just fine, but one of the other jobs of the internal thermostat is probably to keep the evaporator from freezing, so you might want to be careful and experiment.

I built a circulation fan for my kegerator, out of a small Folgers can and an 80mm computer fan, and an old cell phone charger. I pointed it right at my factory internal thermostat in the mini fridge. Helps keep the air moving so no cold spots develop on the evaporator, and helps the thermostat to read the air temperature more accurately.

I'm also thinking the STC-1000 is used to control 110V AC lines, and the internal thermostat in that mini-fridge is probably 12-24 volts DC. Not sure if that would have any effect on it, as I'm not more familiar with that particular device.

 

[disney7]

Sweet.

A somewhat related question. If the compressor were to run too long, could it eventually freeze the refrigerant? Or will it only get down to a certain temp and no go any colder?

Also, what is a good delay setting in minutes to keep from short cycling the compressor?

Thanks!

 

[mblanks2]

Sweet.

A somewhat related question. If the compressor were to run too long, could it eventually freeze the refrigerant? Or will it only get down to a certain temp and no go any colder?

Also, what is a good delay setting in minutes to keep from short cycling the compressor?

Thanks!

The refrigerant itself won't freeze. The evaporator might. Is the evaporator in an area that can capture the moisture and drain it out of the frig or would it just run into the floor of the frig?

Anti-short cycle at 5 minutes should protect your compressor just fine.

 

[disney7]

The evaporator is that cooling panel I guess. Any condensation or melt will run off it into a little drain and into a pan in the back of the fridge.

I guess these things don't really have a condenser? At least not a radiator type like a car has?

 

[mblanks2]

The evaporator is that cooling panel I guess. Any condensation or melt will run off it into a little drain and into a pan in the back of the fridge.

I guess these things don't really have a condenser? At least not a radiator type like a car has?

You should be fine with the STC 1000. Hook it up and try it out for few days to see how it reacts. The drain is there because it will freeze/frost. Perfectly normal. If you want a fan inside wire it into the line side of the switch and it will run continuously but isn't really necessary.

 

[Blitzkrieg]

I wired the exact same fridge up direct a few weeks ago with the stc-1000... Replaced the factory thermostat completely and put the stc in its place. I have my temp probe taped to my carboy that is lagering right now and when I cold crashed from room temp down down to 33°f the compressor ran for about 36 hours straight with no problems. There was some ice that formed on the condenser but it has since melted and disappeared into the drain.

This is how it looks with the stc in factory position, only downfall is that you have to open the fridge to change temp. The upside is that I didn't need any project box or receptacles to wire it in.


Sent from my iPhone using Home Brew

 

[disney7]

Sweet! Do you think the STC Will have any problems from moisture from being inside the fridge?

 

[mblanks2]

Sweet! Do you think the STC Will have any problems from moisture from being inside the fridge?

It is rated for 20% to 85% relative humidity locations but does state "No Condensate" in that rating. With the internal mounting, condensation is very possible.
I personally would consider an external mount with just the probe inside.

 

[Blitzkrieg]

Hmmm, never thought of that... The only place that condensate seems to form in the fridge is on the condenser as far as I have seen. Maybe it's designed that way? I'll pop the cover later today to see if there is any condensate in there.


Sent from my iPhone using Home Brew

 

[JPrather]

Hmmm, never thought of that... The only place that condensate seems to form in the fridge is on the condenser as far as I have seen. Maybe it's designed that way? I'll pop the cover later today to see if there is any condensate in there.

Hopefully it works okay like that because that's freakin' slick. Was that a relatively simple install (as far as STC's go anyway)?

I just got an older Danby Millenium wine chiller/mini fridge that's the same basic unit, and it seems to be doing an *ok* job of lagering my Altbier, but I'm likely going to be getting a temperature controller eventually. I was looking at a Ranco/Johnson type deal but after seeing your build I'm tempted to try the STC route. That looks freaking slick!

 

[Blitzkrieg]

It actually wasn't bad at all, all the wiring you need is already under that cover and it just happened to be the right size (with some cutting of course) to fit the stc. The only pain, like I said was getting all the wiring to fit in there neatly. Probably would have been easier had I used smaller wire nuts, but I had the yellow ones on hand. And I checked this weekend, no condensation under the cover. I will keep an eye on that though when the summer months bring back the heat and humidity.

 

[disney7]

Blitzkrieg, did you bypass the light switch and use the wires for the light bulb as power for the STC?

 

[Blitzkrieg]

No, I left the light hooked up and branched the hot wire 3 ways; one for the STC, 1 for cooling, and 1 for heating. For now I just removed the light bulb so that it won't run constantly, I havent found the type of paneling I want to cover the door foam yet so theres nothing to turn the switch on and off. I did cut the light neutral in order to split it in two; one for the light, one for the STC.

 

[disney7]

I haven't put a meter on it yet. Is one of the non-ground wires that ran to the thermostat always hot?

 

[Blitzkrieg]

Yeah, the thermostat has one always hot, and one that switches on and off with temp changes. There should be no neutral that runs to the thermostat, the compressor's neutral is hard wired in the back of the fridge from the plug. The only neutral you should have in the housing should be going to the light.