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Date: 07 Jun 2006 23:21:29
From: HAL 9000
Subject: Has anyone modified a freezer thermostat?
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Today I got around to inspecting the thermostat on my new freezer. I don't
have much experience with refrigeration controls, but I can't seem to figure
out how the thermostat works. And I can't find any specs for it online.
It has 3 wires running to it, plus a ground wire, and a pressure probe which
obviously actuates an internal switch depending on the temperature.
What's odd to me is when I check continuity on the leads they all seem
shorted together regardless of the position of the thermostat setting,
including off. Yet when plugged in it turns the compressor on and off just
fine. I'm missing something.
The part # for the thermostat is 216714700. I've found replacement parts
for it, but no specs.
There's what looks like a small adjustment screw, but I can't determine what
effect it has. I was hoping I could turn the freezer on and adjust the
screw until it went off. I guess there's more to it.
Any help would be great. Thanks.
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Date: 07 Jun 2006 21:19:08
From: Wayne
Subject: Re: Has anyone modified a freezer thermostat?
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HAL 9000 wrote:
> What's odd to me is when I check continuity on the leads they all seem
> shorted together regardless of the position of the thermostat setting,
> including off. Yet when plugged in it turns the compressor on and off just
> fine. I'm missing something.
>
What you are missing is what is actually happening in the thermostat.
The theromstat is not a normal on/off switch like a light switch.
Rather, the thermostat senses changes in resistance in the thermocouple
caused by the change in temperature. Yes, everything is shorted
together. What changes is the resistance value. I am too tired and
have had too many beers at the moment to fully explain the physics and
electronics involved. There are probably others that can explain it better.
Wayne
Bugeater Brewing Company
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Date: 08 Jun 2006 03:20:16
From: HAL 9000
Subject: Re: Has anyone modified a freezer thermostat?
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"Wayne" <bugeaterbrewing@charter.net > wrote in message
news:fPLhg.49$0I2.24@fe06.lga...
> HAL 9000 wrote:
>> What's odd to me is when I check continuity on the leads they all seem
>> shorted together regardless of the position of the thermostat setting,
>> including off. Yet when plugged in it turns the compressor on and off
>> just fine. I'm missing something.
>>
>
> What you are missing is what is actually happening in the thermostat. The
> theromstat is not a normal on/off switch like a light switch. Rather, the
> thermostat senses changes in resistance in the thermocouple caused by the
> change in temperature. Yes, everything is shorted together. What changes
> is the resistance value. I am too tired and have had too many beers at
> the moment to fully explain the physics and electronics involved. There
> are probably others that can explain it better.
>
>
> Wayne
> Bugeater Brewing Company
It must be along those lines, though the resistance is almost zero on all
leads, I checked for that initially. I am actually familiar with
thermocouples. In this case, there isn't a thermocouple, it has a pressure
probe, which does operate an on off switch as the pressure is related to
temperature and expansion pushes a switch as the diaphragm moves in or out
with the pressure/temperature. That switch is internal though and operates
some other circuitry that I don't have specs for and isn't reading obvious
changes in resistance with a meter. The compressor itself has a box on it
too that probably has some sort of control function. I'm not sure how that
ties in. Maybe the thermo only directs a small current into a transistor at
the compressor side or something like that?
I'm waiting for a temperature sensor that will solve my problem after I get
some programming into an AVR setup for it, but until then I'm manually
running things. Luckily the freezer stays cold well when it's off. It's
going to take me awhile to get digital temp control going, so I was hoping
somebody could clue me in on how to adjust the stock analog thermo. I'm
kinda thinking the screw I mentioned is for adjustment, but above freezing
might still be out of its range? Maybe if I pop the backing off I can
change that, but then I'm risking breaking things maybe. So maybe somebody
can save me a mistake there.
Thanks for the reply. Any input is appreciated.
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Date: 08 Jun 2006 04:48:03
From: Scott Sellers
Subject: Re: Has anyone modified a freezer thermostat?
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HAL 9000 <SorryDave@Icantdothat.com >:
[...]
>It must be along those lines, though the resistance is almost
>zero on all leads, I checked for that initially. I am
>actually familiar with thermocouples. In this case, there isn't
>a thermocouple, it has a pressure probe, which does operate an
>on off switch as the pressure is related to temperature and
>expansion pushes a switch as the diaphragm moves in or out with
>the pressure/temperature. That switch is internal though and
>operates some other circuitry that I don't have specs for and
>isn't reading obvious changes in resistance with a meter. The
>compressor itself has a box on it too that probably has some
>sort of control function. I'm not sure how that ties in. Maybe
>the thermo only directs a small current into a transistor at the
>compressor side or something like that?
No real expertise in electronics, but I'm guessing it could be a
relay on the compressor, activated by current switched in the
thermostat.
>I'm waiting for a temperature sensor that will solve my problem
>after I get some programming into an AVR setup for it, but until
>then I'm manually running things. Luckily the freezer stays
>cold well when it's off. It's going to take me awhile to get
>digital temp control going, so I was hoping somebody could clue
>me in on how to adjust the stock analog thermo. I'm kinda
>thinking the screw I mentioned is for adjustment, but above
>freezing might still be out of its range? Maybe if I pop the
>backing off I can change that, but then I'm risking breaking
>things maybe. So maybe somebody can save me a mistake there.
Even if the screw is for temperature adjustment, it's probably in
the range that freezers are meant to operate. If you could easily
adjust one to fermentation temp, I think we'd all be doing it,
instead of buying controllers. ;)
A programmable controller sounds cool.
I wouldn't risk breaking the t-stat though, because it could
render the freezer inoperable, or at least cost enough to replace
that you might have gotten a temp controller instead.
FWIW, I have a ranco etc-141000, found on ebay, pristine
condition, for considerably less than the prices quoted in this
thread. Works great.
Scott
--
Scott Sellers
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Date: 08 Jun 2006 20:25:22
From: HAL 9000
Subject: Re: Has anyone modified a freezer thermostat?
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"Scott Sellers" <scottsellers@mindspring.com > wrote in message
news:7_Nhg.3017$o4.315@newsread2.news.pas.earthlink.net...
> HAL 9000 <SorryDave@Icantdothat.com>:
> I wouldn't risk breaking the t-stat though, because it could
> render the freezer inoperable, or at least cost enough to replace
> that you might have gotten a temp controller instead.
I was thinking the same thing. Especially since I don't have a handle on
what the thermostat is doing yet and am not sure how to "hot-wire" it
without it the thermo. So if I break it I might need to buy a $40
replacement and then I could have about bought an external controller. But
it looks doable, I was hoping somebody has fooled with something similar and
might have some tips. Somewhere, I can't recall where, I read a comment by
someone that they had to modify a thermostat. There was no further
elaboration though.
> FWIW, I have a ranco etc-141000, found on ebay, pristine
> condition, for considerably less than the prices quoted in this
> thread. Works great.
Thanks, I'll investigate that.
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Date: 09 Jun 2006 10:28:14
From: Adrian Levi
Subject: Re: Has anyone modified a freezer thermostat?
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HAL 9000 wrote:
> Today I got around to inspecting the thermostat on my new freezer. I don't
> have much experience with refrigeration controls, but I can't seem to figure
> out how the thermostat works. And I can't find any specs for it online.
>
> It has 3 wires running to it, plus a ground wire, and a pressure probe which
> obviously actuates an internal switch depending on the temperature.
>
> What's odd to me is when I check continuity on the leads they all seem
> shorted together regardless of the position of the thermostat setting,
> including off. Yet when plugged in it turns the compressor on and off just
> fine. I'm missing something.
>
> The part # for the thermostat is 216714700. I've found replacement parts
> for it, but no specs.
>
> There's what looks like a small adjustment screw, but I can't determine what
> effect it has. I was hoping I could turn the freezer on and adjust the
> screw until it went off. I guess there's more to it.
>
> Any help would be great. Thanks.
I'm assuming that the screw adjustment is going to be your differential
temp ie your set temp (set with the main knob) plus your differential
(2-3°C) is your cut in temp.
one of the three wires is most likely a swich wire to turn on a defrost
heater in a drain tray somewhere. Is it a cyclic defrost or fully frost
free? Cyclic defrost fridges have an exposed evaporator up the back.
If this is the case then the terminals on the thermostat should be a
common, normally open and normally closed.
HTH Adrian
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Date: 08 Jun 2006 22:46:11
From: HAL 9000
Subject: Re: Has anyone modified a freezer thermostat?
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"Adrian Levi" <hoarder@exampleoptushome.com.au > wrote in message
news:4488183f$0$10014$afc38c87@news.optusnet.com.au...
> I'm assuming that the screw adjustment is going to be your differential
> temp ie your set temp (set with the main knob) plus your differential
> (2-3°C) is your cut in temp.
You're saying that controls the hysteresis, how much it fluctuates around
the setpoint? That would make sense.
> one of the three wires is most likely a swich wire to turn on a defrost
> heater in a drain tray somewhere. Is it a cyclic defrost or fully frost
> free? Cyclic defrost fridges have an exposed evaporator up the back.
It doesn't have an exposed evaporator, but I believe it is manual defrost.
I'll try to verify that further.
The freezer is G.E. Model# FCM 15CMB WH
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Date: 09 Jun 2006 21:17:00
From: Adrian Levi
Subject: Re: Has anyone modified a freezer thermostat?
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HAL 9000 wrote:
> "Adrian Levi" <hoarder@exampleoptushome.com.au> wrote in message
> news:4488183f$0$10014$afc38c87@news.optusnet.com.au...
> > I'm assuming that the screw adjustment is going to be your differential
>> temp ie your set temp (set with the main knob) plus your differential
>> (2-3°C) is your cut in temp.
>
> You're saying that controls the hysteresis, how much it fluctuates around
> the setpoint? That would make sense.
That's right, set point for example -18°C plus 3°C differential makes
cut in -15°C and cut out -18°C.
>> one of the three wires is most likely a swich wire to turn on a defrost
>> heater in a drain tray somewhere. Is it a cyclic defrost or fully frost
>> free? Cyclic defrost fridges have an exposed evaporator up the back.
>
> It doesn't have an exposed evaporator, but I believe it is manual defrost.
> I'll try to verify that further.
> The freezer is G.E. Model# FCM 15CMB WH
Sorry didn't realise that the unit was a chest freezer, Makes the
mysterious third wire intriguing. Can you post a wiring diagram?
Adrian
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Date: 09 Jun 2006 06:08:49
From: HAL 9000
Subject: Re: Has anyone modified a freezer thermostat?
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"Adrian Levi" <hoarder@exampleoptushome.com.au > wrote in message
news:4488b08a$0$370$afc38c87@news.optusnet.com.au...
. Can you post a wiring diagram?
>
> Adrian
If all else fails, read the directions. I found the schematics in an
envelope on the back of the freezer. Duh. AFTER I popped open the
thermostat of course.
The 3rd wire goes to a temperature monitor/alarm.
It is almost as simple as I thought at first. The thermostat turns a relay
on or off. The relay connects/disconnects a hot wire to the compressor &
temp. alarm. Somehow I screwed up the continuity readings because it should
have shown a disconnect between the main hot wire and the other two
terminals when the thermo is off. But checking every combination for 3
leads while turning a dial and sitting on the floor in a half-dark garage .
. . I should have been more meticulous though.
It turns out the small taped-over screw *is* a temperature control
adjustment, not hysteresis. It tightens or loosens tension on a spring that
the diaphragm of the temperature probe rides on. And, after I popped a
couple parts off I could see the screw was labeled with an engraving "Colder
=== >".
Now that I've figured out how it all works, I've got the thermostat apart
and can't figure out how to get one of the springs back into it properly.
I'll have to spend more time with that.
At least now that I know what the thermo does. I can hotwire it by hooking
all the leads together, which is what happens when the thermo kicks on the
relay. It works fine that way. So I'm no worse off without the thermostat
for brewing purposes; I've got an on/off freezer.
I also pulled the temperature probe all the way out and found it has no bulb
on the end of it (it's just a capillary tube), so I'm wondering if that may
limit the range of the adjusting screw to sub freezing temperatures. The
Johnson temp controller, for example, has a rather large bulb at the end of
the capilary tube; which of course determine how much movement there is at
the diaphragm side at given pressure/temperatures; it just might not be
possible to work with this thermostat because of that.
All this has got me thinking though, I wonder if there's an appliance
junkyard somewhere in my area?
In the mean time, I'm waiting for my digital temperature sensor, then this
will all be moot.
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Date: 09 Jun 2006 17:54:57
From: Homebrew Exchange
Subject: Re: Has anyone modified a freezer thermostat?
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You know, Johnson Controls makes a thermostat that you just plug into
the wall, plug the fridge into that, then put the probe into the
fridge. No wiring, no modifications. It costs around $60, but seems
like the easiest way to go. I'm getting an old fridge this week and I'm
going to pick one up.
Dave
www.homebrew-exchange.com
HAL 9000 wrote:
> "Adrian Levi" <hoarder@exampleoptushome.com.au> wrote in message
> news:4488b08a$0$370$afc38c87@news.optusnet.com.au...
> . Can you post a wiring diagram?
> >
> > Adrian
>
> If all else fails, read the directions. I found the schematics in an
> envelope on the back of the freezer. Duh. AFTER I popped open the
> thermostat of course.
>
> The 3rd wire goes to a temperature monitor/alarm.
>
>
> It is almost as simple as I thought at first. The thermostat turns a relay
> on or off. The relay connects/disconnects a hot wire to the compressor &
> temp. alarm. Somehow I screwed up the continuity readings because it should
> have shown a disconnect between the main hot wire and the other two
> terminals when the thermo is off. But checking every combination for 3
> leads while turning a dial and sitting on the floor in a half-dark garage .
> . . I should have been more meticulous though.
>
> It turns out the small taped-over screw *is* a temperature control
> adjustment, not hysteresis. It tightens or loosens tension on a spring that
> the diaphragm of the temperature probe rides on. And, after I popped a
> couple parts off I could see the screw was labeled with an engraving "Colder
> ===>".
>
> Now that I've figured out how it all works, I've got the thermostat apart
> and can't figure out how to get one of the springs back into it properly.
> I'll have to spend more time with that.
>
> At least now that I know what the thermo does. I can hotwire it by hooking
> all the leads together, which is what happens when the thermo kicks on the
> relay. It works fine that way. So I'm no worse off without the thermostat
> for brewing purposes; I've got an on/off freezer.
>
> I also pulled the temperature probe all the way out and found it has no bulb
> on the end of it (it's just a capillary tube), so I'm wondering if that may
> limit the range of the adjusting screw to sub freezing temperatures. The
> Johnson temp controller, for example, has a rather large bulb at the end of
> the capilary tube; which of course determine how much movement there is at
> the diaphragm side at given pressure/temperatures; it just might not be
> possible to work with this thermostat because of that.
>
> All this has got me thinking though, I wonder if there's an appliance
> junkyard somewhere in my area?
>
> In the mean time, I'm waiting for my digital temperature sensor, then this
> will all be moot.
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Date: 10 Jun 2006 20:44:25
From: HAL 9000
Subject: Re: Has anyone modified a freezer thermostat?
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"Homebrew Exchange" <dave_ward@homebrew-exchange.com > wrote in message
news:1149900897.678598.114650@g10g2000cwb.googlegroups.com...
> You know, Johnson Controls makes a thermostat that you just plug into
> the wall, plug the fridge into that, then put the probe into the
> fridge. No wiring, no modifications. It costs around $60, but seems
> like the easiest way to go. I'm getting an old fridge this week and I'm
> going to pick one up.
>
> Dave
> www.homebrew-exchange.com
>
For $5 I've got a digital sensor on the way that will go right into a device
I already have built and the problem will be solved..
For the group and my immediate needs an alternative solution for under $15
should be possible. I guess the problem should be presented to an HVAC
group, since it doesn't seem to have been tackled well here yet.
$60 and up for a basic non-programmable thermostat is ridiculous to me. A
50% increase on the cost of my 2-year old used freezer?
If I didn't have the digital option, I'd just go down to a thrift store and
pick up a waterbed thermostat for a $1 and wire it to a cheap relay. Total
cost maybe $5 if you wire it into the freezer's power cord. Same thing as
the Johnson analog model.
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Date: 10 Jun 2006 21:16:12
From: HAL 9000
Subject: Re: Has anyone modified a freezer thermostat?
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"HAL 9000" <SorryDave@Icantdothat.com > wrote in message
news:JaGig.449$db5.28@trnddc03...
>
> If I didn't have the digital option, I'd just go down to a thrift store
> and pick up a waterbed thermostat for a $1 and wire it to a cheap relay.
> Total cost maybe $5 if you wire it into the freezer's power cord. Same
> thing as the Johnson analog model.
Actually, I think I will do that since modifying the existing thermostat for
free either isn't possible because of the type of probe or at least I
haven't been able to figure out how.
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Date: 11 Jun 2006 12:10:40
From: Dick Adams
Subject: Re: Has anyone modified a freezer thermostat?
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HAL 9000 <SorryDave@Icantdothat.com > wrote:
> For $5 I've got a digital sensor on the way that will go right
> into a device I already have built and the problem will be solved.
>
> For the group and my immediate needs an alternative solution
> for under $15 should be possible. I guess the problem should
> be presented to an HVAC group, since it doesn't seem to have
> been tackled well here yet. ....
It would be a gross understatement to say a detailed explantion
would be appreciated.
Dick
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Date: 29 Jun 2006 18:40:57
From:
Subject: Re: Has anyone modified a freezer thermostat?
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http://groups.google.com/group/rec.crafts.brewing/browse_thread/thread/541c32dc623bb81e/6c0813fbf3ef5e3d?rnum=1#6c0813fbf3ef5e3d
Lots of options. Check about 4 days ago- temperature controller ranco
I made my own for 54$ + electrical cord.
SanDiegoBrewGuy wrote:
> Hal,
>
> This is great! I just bought a chest freezer yesterday and need to rig
> it up to cool my beer. Could you post the fix?
>
> Thx,
> R
>
> Dick Adams wrote:
> > HAL 9000 <SorryDave@Icantdothat.com> wrote:
> >
> > > For $5 I've got a digital sensor on the way that will go right
> > > into a device I already have built and the problem will be solved.
> > >
> > > For the group and my immediate needs an alternative solution
> > > for under $15 should be possible. I guess the problem should
> > > be presented to an HVAC group, since it doesn't seem to have
> > > been tackled well here yet. ....
> >
> > It would be a gross understatement to say a detailed explantion
> > would be appreciated.
> >
> > Dick
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