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Post by coldspaces on Aug 2, 2016 1:37:30 GMT
I have been wanting for a long time to take a two knob control apart and see just how it all works and what the chances of repairing them are. So last week I realized I had one that wasn't doing much in the CA form A machine I tried to make work on a TXV, so home it came and sat waiting for me to find time to play. Here is all the info on the outside. It sure looks like someone tried to get into this control in the past. You can see signs they tried to get the plug out that hides the cover screw. I ended up drilling a hole in the plug with a small drill bit turned by my fingers. Something small and sticky or a tiny suction cup might have pulled it out without damage. Here is whats inside. Gotta chill out the sensing bulb next, THIS IS A MUST OR IRREVERSIBLE DAMAGE MAY OCCUR TO THE BELLOWS WHEN IT OVER EXPANDS. From my studies of the inside of this control the bellows must be removed before much of the control can be dissembled. Some salt,ice and a little water soon had me a 7 degree Fahrenheit brine to placed the sensing tube in.
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Post by coldspaces on Aug 2, 2016 1:48:40 GMT
The nuts that hold the screws for the bellows are circled here in red. I also added the black reference mark you see but it wasn't needed. All chilled out and ready to remove the bellows. Keeping the sensing tube in the cold brine I removed the control from it. Here you see the sloped edge washer that fits over the end of the bellows. And under it is another flat brass washer. Looks like the bellows was outsourced.
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Post by coldspaces on Aug 2, 2016 1:57:20 GMT
A little plumbers strap made a quick retainer to keep the bellows from over expanding when removed from the cold brine. I took it in the house for now so it won't see the heat that can build up in my garage. And a shot with the bellows out.
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Post by Travis on Aug 2, 2016 2:02:12 GMT
Very useful info. The time of repairing what we have is approaching. I have some spare parts, but none that I could guarantee.
This will be helpful to Ray. He's getting one of those controls with a bad switch from me.
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Post by coldspaces on Aug 2, 2016 3:01:09 GMT
The first lever that must come out is the one I labeled as A at both ends. It can not be removed till the bridle spring (BS) is unhooked from the bridle and the pressure from the temperature adjusting spring (T) removed from lever A. It took a small pair of tweezers to get the bridle spring off of the bridle. Here you can see the spring is unhooked from the Bridle. I used two thin wrenches to compress spring T, I held it compressed with one hand while I carefully removed lever A. Take take your time and the bridle and lever A will clear everything else and come out. So far so good.
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Post by ckfan on Aug 2, 2016 13:52:01 GMT
Wow, very good! This is very useful stuff. Thank you for taking the time to do this. If my eyes are correct, it looks like the contacts aren't even that bad. This thermostat is a little more complex than the one that was in my freezer.
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Post by coldspaces on Aug 2, 2016 17:19:32 GMT
This thermostat is a little more complex than the one that was in my freezer. The newest understatement of the year LOL
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Post by coldspaces on Aug 3, 2016 3:08:05 GMT
This is one busy control. Its a challenge to describe it all accurately. I hope the names I give the parts all make sense as I am not sure just what the factory called them all. The lever I have labeled (D) is the one that activates the defrost when the left knob with its defrost cam (DC) is turned to the defrost position. The spring with lever D I labeled (DS) for defrost spring. If you look you will see one end of DS (Green circle) is behind the Temperature adjusting cone (TAC). The spring tension on the defrost lever varies as you adjust the control setting. The yellow circle shows the end of the raised area that TAC is guided on. TAC does not turn, only moves back and forth. Here is another view of the DS spring and the raised track that TAC is guided by. Retainer (R) slips out and lets the right knob move out so it will miss its stop and turn all the way around, thus allowing one to unscrew the knob and threaded shaft from TAC. I started with the knob in the coldest position and found it took 3 1/2 turns to un thread the shaft from TACNow you can really see the end of Spring DS Nowhere in the control is there any sign of a lubricant used on any moving parts,even these threads are bare.
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Post by ChrisJ on Aug 3, 2016 19:18:40 GMT
Fantastic thread.
It should be noted that the 1933 form A and 1934 form B controls are slightly different. The temp swing is a little colder on the form B and it also snaps back from defrost to On automatically.
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Post by timeswelding on Aug 3, 2016 19:56:34 GMT
Great write-up. Thanks for taking the time as I have no doubt it will help a lot of us. I find it interesting they went to the expense of using a double lead thread for the temperature adjusting screw. Perhaps it is the only way that they could achieve a course enough thread. Otherwise, it'd be 1.5 full turns from warmest to coldest instead of 3/4 turn. Smart.
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Post by cablehack on Aug 3, 2016 23:16:08 GMT
Thanks for the dissection. I did notice the lack of lubricant with my own controls and wondered if it was because of the fear it could become sticky and interfere with the calibration. I know this was the opinion of some radio manufacturers who did not lubricate the dial pulleys because over time they knew it would probably gum up after a while (it often did).
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Post by coldspaces on Aug 3, 2016 23:41:52 GMT
Thanks for the dissection. I did notice the lack of lubricant with my own controls and wondered if it was because of the fear it could become sticky and interfere with the calibration. I know this was the opinion of some radio manufacturers who did not lubricate the dial pulleys because over time they knew it would probably gum up after a while (it often did). That could be and also grease attracts dust, plus maybe they didn't want any thing to contaminate the electrical contacts.
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Post by ChrisJ on Aug 4, 2016 14:20:09 GMT
I think I finally see why my control will only go so cold and stops turning the machine back on. It looks like, if you thread the collar against the spring too far, you loose all "spring" movement and it'll simply hold the contacts open.
Does that seem correct coldspaces?
Best I could do, was adjust the control warmer until it would kick back on, and then go a hair warmer for good measure and set that was #9 on my control. This yields between 32-34F cabinet temp on my form A machine. Apparently, a form B control will run slightly colder, and a CK control even colder yet the 1933 form A control being the warmest of the designs.
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Post by coldspaces on Aug 6, 2016 1:59:42 GMT
I think I finally see why my control will only go so cold and stops turning the machine back on. It looks like, if you thread the collar against the spring too far, you loose all "spring" movement and it'll simply hold the contacts open. Does that seem correct coldspaces? Best I could do, was adjust the control warmer until it would kick back on, and then go a hair warmer for good measure and set that was #9 on my control. This yields between 32-34F cabinet temp on my form A machine. Apparently, a form B control will run slightly colder, and a CK control even colder yet the 1933 form A control being the warmest of the designs. I would say that all depends on the pressure from the bellows. At this point the bellows is still out of my control and even with it in the coldest position there is still some spring pressure for the bellows to overcome. I can push with my finger were the bellows belongs and cause the contacts to close.
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Post by coldspaces on Aug 6, 2016 2:06:11 GMT
Here is the front view you can see the stop for the knob. Red arrow shows the clip I removed to get the defrost lever out. Be careful they tend to fly around when removed but I found it. Here are a couple of views of the defrost lever and spring.
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