Kegconnection Complete Starter Kit and More Giveaway!


Home Brew Forums > Home Brewing Beer > DIY Projects > Guide to set internal chest freezer thermostat to >32F; Eliminate external control

Reply
 
LinkBack Thread Tools
Old 06-05-2011, 07:55 PM   #1
AssistantBrewer
Feedback Score: 0 reviews
Recipes 
 
Join Date: Jun 2011
Location: Littleton, CO
Posts: 8
Liked 20 Times on 2 Posts

Default Guide to set internal chest freezer thermostat to >32F; Eliminate external control

Typical keezer conversion instructions shown here on HBT and elsewhere indicate that an external temperature controller is required. However, this is not true. The frugal and patient DIYer can spend that money elsewhere.

The vast majority of chest freezers used for keezer conversions utilize a simple internal electromechanical thermostat. These thermostats are preset by the factory to operate with a typical range between -20F and 20F depending on the position of the user accessible dial. Keezer temperatures are in the 40F range, depending on taste. It is the inability to readily set the internal thermostat to keezer appropriate temperatures that drives the need for an external thermostat. Here is an example of a typical internal thermostat:



What is not widely known is how these electromechanical thermostats work, and that these internal freezer thermostats have a coarse temperature adjustment screw which can be used to widely adjust the temperature setting of the thermostat, even above freezing to keezer temps. The coarse adjust screw on the unit pictured above is in the 5 o'clock position relative to the fine adjust dial shaft. They are usually recessed within the unit and may be covered with tape. Some units have them on the side, but I have yet to find one without a coarse adjustment screw.

Electromechanical thermostats operate on the principle of the ideal gas law, PV=NkT, where P=Pressure, V=Volume, N=Number of gas particles, k=Boltzmann’s constant, and T=Temperature in Kelvin. The idea is that by sealing a quantity of gas in an enclosed vessel the variables V, N, and k are held constant resulting in the pressure of the gas being directly proportional to its temperature.

Freezer thermostats use a long hollow tube as the enclosed vessel that is stuffed inside the freezer wall, with a short portion extending into the compressor compartment where one end is connected to a pressure sensor. The pressure sensor works by movement of a diaphragm set against a spring. The important part is that to overcome manufacturing and material process variables and to allow use of the same design for different applications the spring tension is designed to be widely adjustable by manipulation of the coarse set screw.

From the ideal gas law we know that at higher temperatures equal higher pressure against the diaphragm. Thus, to adjust the thermostat to trigger at a higher temperature the opposing spring force must be increased. Increased spring tension can be felt as increased resistance when turning the coarse adjustment screw. Below is a simplified diagram detailing the principle.



Some trial and error can be required to get the setting correct, and this is where patience comes in as it can take several hours for the temperature inside the freezer to come to steady state. Quick coarse temperature measurements can be made with a dry thermometer, but since hysteresis can result in several degrees of error final measurements should be made with a thermometer with some thermal mass for final adjustment (i.e. a floating thermometer in a glass of water).

CAUTION: Since the thermostat switches line voltage to the compressor there is live electrical current inside the thermostat at all times when the freezer is powered. REMOVE POWER FROM THE FREEZER BEFORE ADJUSTING THE INTERNAL COARSE SET SCREW.

AssistantBrewer

__________________
AssistantBrewer is offline
26
People Like This 
Reply With Quote Quick reply to this message
Old 06-05-2011, 08:10 PM   #2
pauljmccain
Feedback Score: 0 reviews
Recipes 
 
Join Date: May 2011
Location: St. Louis, Missouri
Posts: 191
Default

I'm going to try this, thanks! So glad I saw it- I was literally just about to walk out to install my johnson controller on my in-progress keezer.

__________________
pauljmccain is offline
 
Reply With Quote Quick reply to this message
Old 06-05-2011, 08:48 PM   #3
Reno_eNVy
HBT_SUPPORTER.png
Feedback Score: 0 reviews
 
Reno_eNVy's Avatar
Recipes 
 
Join Date: Oct 2008
Location: Reno, Nevada
Posts: 6,152
Liked 191 Times on 162 Posts
Likes Given: 60

Default

Subscribed! Awesome. I'm almost done with a chest freezer conversion, almost ready to attach the controller. I checked the compressor housing on the freezer and there is a little cover over where, I'm assuming, the internal controller and adjustment knobs are. Time for a bit of exploration.

__________________
Primary: air and sadness =(

Kegged: Cascadian Dark Ale

Bottled: English Barleywine (brewed 9/26/09 -- bottled 5/5/10)


LET'S GO LA!
LA CAMPEONES!
PLAY FOR GLORY, THE GLORY LA!
Reno_eNVy is offline
 
Reply With Quote Quick reply to this message
Old 06-05-2011, 09:19 PM   #4
AssistantBrewer
Feedback Score: 0 reviews
Recipes 
 
Join Date: Jun 2011
Location: Littleton, CO
Posts: 8
Liked 20 Times on 2 Posts

Default

Glad to have helped. I haven't seen this information posted before.

Here's another thermostat with the coarse set screw on the side. This one was staked in place with some blue Loctite at the factory. It didn't take much to pop the Loctite.



AssistantBrewer

__________________
AssistantBrewer is offline
 
Reply With Quote Quick reply to this message
Old 06-05-2011, 09:27 PM   #5
Jem
Feedback Score: 0 reviews
Recipes 
 
Join Date: Jan 2011
Location: St Paul, mn
Posts: 90
Liked 3 Times on 2 Posts

Default

Subscribed. This helps move the keezer project up from a budget standpoint.

__________________
Jem is offline
 
Reply With Quote Quick reply to this message
Old 06-05-2011, 10:09 PM   #6
shortyjacobs
Feedback Score: 0 reviews
Recipes 
 
Join Date: Aug 2009
Location: Twin Cities, MN
Posts: 2,511
Liked 29 Times on 29 Posts
Likes Given: 3

Default

Wow, great info. Thanks!

__________________
Itchy Dog Brewery.

(As of 10-24-2011)
Primary - Steppe 112 PA, 2x Monday RyePA
Aging - None :-(
On tap - Big Dog, Apfelwein, Steppe 112 PA

My invisible AG sculpture, with no actual sculpture and a tiny footprint.
My Kegerator goes offroading!
My Coors Home Draft dispenser for boating/beering on the go.
shortyjacobs is offline
 
Reply With Quote Quick reply to this message
Old 06-06-2011, 11:51 AM   #7
carrotmalt
Feedback Score: 0 reviews
Recipes 
 
Join Date: Oct 2008
Location: .
Posts: 469
Liked 6 Times on 5 Posts
Likes Given: 1

Default

So looking at the diagram, it looks like I'd be loosening (lefty loosy) the screw to get it above freezing right? In your experience, how many turns should I start off with for my first stab at 40 degrees? I'd love to not have to buy another controller for my keezer build!!!

__________________

I like a little more beer in my beer.

carrotmalt is offline
ashkanr Likes This 
Reply With Quote Quick reply to this message
Old 06-06-2011, 02:03 PM   #8
redman67
HBT_SUPPORTER.png
Feedback Score: 11 reviews
 
redman67's Avatar
Recipes 
 
Join Date: Feb 2010
Location: Taunton, MA
Posts: 396
Liked 15 Times on 12 Posts
Likes Given: 7

Default

Great info Thanks

__________________

Because God hates it when you drink bad beer

redman67 is offline
 
Reply With Quote Quick reply to this message
Old 06-06-2011, 02:13 PM   #9
jsguitar
HBT_SUPPORTER.png
Feedback Score: 0 reviews
 
jsguitar's Avatar
Recipes 
 
Join Date: May 2011
Location: Overland Park, KS
Posts: 1,018
Liked 92 Times on 71 Posts
Likes Given: 411

Default

This is excellent info. Prost!

__________________
jsguitar is offline
 
Reply With Quote Quick reply to this message
Old 06-06-2011, 02:19 PM   #10
ajwillys
Feedback Score: 0 reviews
Recipes 
 
Join Date: May 2008
Location: Holly Springs, NC
Posts: 1,315
Liked 23 Times on 21 Posts
Likes Given: 32

Default

Excellent info! I already have a controller on my keezer, but I'm sure I could find other uses for it.

__________________
ajwillys is offline
 
Reply With Quote Quick reply to this message
Reply


Quick Reply
Message:
Options
Thread Tools


Similar Threads
Thread Thread Starter Forum Replies Last Post
External HEX Vs. Internal CoalCracker DIY Projects 20 03-01-2012 05:11 AM
Chest freezer: to bypass (or not) the thermostat paledragon DIY Projects 3 01-28-2011 02:01 AM
anybody know where to get a cheap external thermostat? kair DIY Projects 2 07-24-2010 09:23 PM
External T/stat for chest freezer ILOVEBEER DIY Projects 12 03-22-2010 06:34 AM
Temp Control For Chest Freezer PT Ray DIY Projects 0 01-19-2010 01:26 AM