D Isgett
New Member
1933 CA Form A 7 cu ft
Posts: 10
Location: Quinton, Virginia
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Post by D Isgett on Jan 7, 2022 17:35:28 GMT
Hello, I am in need of a refurbished or possibly rebuild service for the thermostat on my 1933 CA form A. My fridge runs and cools well, it will easily chill the box to 32°. The problem I am having is that the thermostat is not cutting in and out properly. Even when I have it set to 1 it will not satisfy, just wants to keep running. I am very interested in purchasing a refurbished or good working thermostat or am willing to send mine out for rebuild. Or of course if anyone has any advice as to how I might repair it myself. Thanks in advance for your help!
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Post by cablehack on Jan 8, 2022 0:23:32 GMT
One thing to check first is that the frost line is actually up to the header tanks. CA's are prone to a dropping frost line because of the non condensible gas build up. If the frost line is below where the sensing tube is clamped to the evaporator, it won't switch off - but the cabinet temperature can still be cold enough. On that note, check also that the sensing tube is properly clamped, because if there is no metal to metal contact, the tube will only sense the air temperature, which is warmer than the evaporator.
If the fridge is continuously running, I would expect the cabinet temperature to get below 32 degrees. Another diagnostic test is to measure the actual evaporator temperature, because there is another characteristic fault with CA's, which can prevent the evaporator temperature getting low enough. That is, a worn float valve. When this happens, the cycling time deteriorates to the point where it just won't shut off. Eventually, the cabinet temperature won't get down to what it should do.
In summary, it might not actually be the control at fault, but rather incorrect operating conditions of the refrigeration system - more likely with CA's than other models.
If you can switch the compressor on and off with the knob, that eliminates contact faults, and indicates the mechanical linkages inside the control are probably ok.
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D Isgett
New Member
1933 CA Form A 7 cu ft
Posts: 10
Location: Quinton, Virginia
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Post by D Isgett on Jan 8, 2022 4:03:02 GMT
Thanks! I will get it cold again and check the frost line first. It was all the way up and into the tanks when I bled the ncg’s about a year ago. I only have an air thermometer, so I will go out and get a probe thermometer that I can stick right to the metal to see what temps I get. I did notice today that I could lower the thermostat capillary about another 1/4” so I did that. Sure appreciate your help, I’ll post back soon.
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Post by turbokinetic on Jan 9, 2022 14:43:33 GMT
Thanks! I will get it cold again and check the frost line first. It was all the way up and into the tanks when I bled the ncg’s about a year ago. I only have an air thermometer, so I will go out and get a probe thermometer that I can stick right to the metal to see what temps I get. I did notice today that I could lower the thermostat capillary about another 1/4” so I did that. Sure appreciate your help, I’ll post back soon. Hi, I can second what Cablehack said. The CA machines tend to lose performance over time. You've done the correct thing bleeding non-condensible gases from the system. There is a chance that the needle valve in the float mechanism is worn, and not able to close properly to regulate the system pressures. As this wears, it raises the minimum temperature the system can reach. Eventually it reaches a point where the system simply can't get cold enough to turn off the thermostat. If your cooling unit were functioning normally, and the thermostat was failing to turn off - the cabinet would eventually get far colder than 32°F. There is one other possibility. The controls tend to "wear" over time and shift to a colder operating range. It's entirely possible that your control could simply be out of calibration. This can be adjusted fairly easily once you confirm that the evaporator is getting cold enough that it should be cycling off. One cautionary note; the control on these fridges not only is a thermostat, it contains the motor overload circuit breaker. If this control is replaced with any other thermostat, which does not contain an overload protection device; you MUST ABSOLUTELY install an inline overload breaker in the circuit. If this is not done, there is a very serious risk of extreme damage to the compressor, and a serious safety hazard as well. If the float needle seat is worn out, that can be repaired, but it's a specialist job. You can read about it here, in capillary tube conversions, and float needle seat repair threads. Sincerely, David |
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D Isgett
New Member
1933 CA Form A 7 cu ft
Posts: 10
Location: Quinton, Virginia
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Post by D Isgett on Jan 10, 2022 2:00:22 GMT
Thanks Cablehack and David,
I followed up on what Cablehack had said about running the unit and checking the temperatures. I had quite a bit of stock in the fridge (beverages), so I emptied the cabinet completely. Then I started it and let it run into the next day, about 12 hours. My air thermometer on the top shelf was down to 28 degrees. My probe thermometer that I had laying in the evaporator unit read just below 0 degrees. (it only goes down to to zero). The compressor has a new 15 watt oil conditioner, runs quietly and after purging a few months ago for ncg's, the frost line on the evaporator has move up from about 2/3 ways up to completely above the two reservoirs.
I felt like the unit was running well enough and cold enough that I must have another problem. David, I read your posts and videos about the thermostat control and decided to remove it again and check it. I had removed it awhile back when I rewired the entire chiller unit and the light circuit. After that work, the unit would turn on and off properly by the control, but this is when I started having more trouble with the compressor cycling properly. Up to this point, I had always felt that something was wrong with the control in that even though the unit would cycle on and off consistently, making temperature adjustments on the knob seemed to make so real difference.
So I followed the instructions regarding chilling the bellows before removing them from the housing to try to see if the bellows functioned. I filled a tea pitcher with ice and some rock salt and waited about 20 minutes. I had a good frost on the outside of the pitcher, so I then inserted the capillary tube into the brine for another 20 minutes or so. While it was still in the brine, I removed the two screws so that the bellows could be removed. Upon removing, they seemed to be almost entirely retracted. After examining the assembly and tubing and finding no apparent damage, I took the tube out of the brine to observe any changes. Even after the lower part of the tube was warmed by my hand above room temperature, the bellows did not move.
I have come to my conclusion that the bellows must have failed. Would you both agree or disagree? If you think that the bellows are weak or bad, what would you say that my remedy to repair it would be? I am a retired auto mechanic by trade, but not extremely skilled with such things as recharging or soldering like I have seen Dave do successfully on video.
I would be glad to purchase a good working bellow and tube set, another complete control, or send my parts out for service. I would greatly appreciate any recommendations!
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Post by ckfan on Jan 12, 2022 0:15:35 GMT
I would tend to agree. If the tube didn’t move when you put your hand on it to warm it, it’s most likely shot.
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D Isgett
New Member
1933 CA Form A 7 cu ft
Posts: 10
Location: Quinton, Virginia
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Post by D Isgett on Jan 12, 2022 0:49:35 GMT
Thanks ckfan! I know they are hard to come by, but I think I need a replacement or rebuild. I am open to any suggestions. Thanks
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Post by 508gm1 on Jan 12, 2022 20:48:59 GMT
You could retrofit a STC-1000 temperature controller as a temporary measure until you get a proper replacement. At least this would get the refrigerator working properly again. They are cheap and easy to program. I only recommend these because they are easy to retrofit & also easy to remove later once you obtain a proper replacement.
You may have to machine a small copper barrel to keep the sensor snug to the evaporator.
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D Isgett
New Member
1933 CA Form A 7 cu ft
Posts: 10
Location: Quinton, Virginia
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Post by D Isgett on Jan 13, 2022 3:43:48 GMT
Thanks for the advice! I may have to go that route.
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Post by turbokinetic on Jan 13, 2022 14:48:27 GMT
Thanks Cablehack and David, I followed up on what Cablehack had said about running the unit and checking the temperatures. I had quite a bit of stock in the fridge (beverages), so I emptied the cabinet completely. Then I started it and let it run into the next day, about 12 hours. My air thermometer on the top shelf was down to 28 degrees. My probe thermometer that I had laying in the evaporator unit read just below 0 degrees. (it only goes down to to zero). The compressor has a new 15 watt oil conditioner, runs quietly and after purging a few months ago for ncg's, the frost line on the evaporator has move up from about 2/3 ways up to completely above the two reservoirs. I felt like the unit was running well enough and cold enough that I must have another problem. David, I read your posts and videos about the thermostat control and decided to remove it again and check it. I had removed it awhile back when I rewired the entire chiller unit and the light circuit. After that work, the unit would turn on and off properly by the control, but this is when I started having more trouble with the compressor cycling properly. Up to this point, I had always felt that something was wrong with the control in that even though the unit would cycle on and off consistently, making temperature adjustments on the knob seemed to make so real difference. So I followed the instructions regarding chilling the bellows before removing them from the housing to try to see if the bellows functioned. I filled a tea pitcher with ice and some rock salt and waited about 20 minutes. I had a good frost on the outside of the pitcher, so I then inserted the capillary tube into the brine for another 20 minutes or so. While it was still in the brine, I removed the two screws so that the bellows could be removed. Upon removing, they seemed to be almost entirely retracted. After examining the assembly and tubing and finding no apparent damage, I took the tube out of the brine to observe any changes. Even after the lower part of the tube was warmed by my hand above room temperature, the bellows did not move. I have come to my conclusion that the bellows must have failed. Would you both agree or disagree? If you think that the bellows are weak or bad, what would you say that my remedy to repair it would be? I am a retired auto mechanic by trade, but not extremely skilled with such things as recharging or soldering like I have seen Dave do successfully on video. I would be glad to purchase a good working bellow and tube set, another complete control, or send my parts out for service. I would greatly appreciate any recommendations! It does sound like the bellows is bad. If the problem is the tube, but the actual metal bellows its self is not broken, it is possible to repair and recharge it. I might even have another broken control with a good bellows. |
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D Isgett
New Member
1933 CA Form A 7 cu ft
Posts: 10
Location: Quinton, Virginia
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Post by D Isgett on Mar 9, 2022 0:34:03 GMT
I just wanted to let everyone know that our CA is back up and running and very healthy! David repaired the control unit which had a leak in the steel line at the control. He replaced it with an all new copper capillary which was very easy to install. If anyone has an unresponsive control like I did where the bellows do not respond to temperature, this could be your issue as well. Thanks again David! The forum has helped yet another owner preserve these machines!
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Post by turbokinetic on Mar 9, 2022 1:11:49 GMT
I just wanted to let everyone know that our CA is back up and running and very healthy! David repaired the control unit which had a leak in the steel line at the control. He replaced it with an all new copper capillary which was very easy to install. If anyone has an unresponsive control like I did where the bellows do not respond to temperature, this could be your issue as well. Thanks again David! The forum has helped yet another owner preserve these machines! Very happy to help! Here is the video where I test it. https://youtu.be/k5SvwDFAhqE |
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Post by ckfan on Mar 11, 2022 14:02:57 GMT
So glad to see this fixed. David is a great guy and is so knowledgeable. It also looks like it’s in good hands now as you know what it takes to keep a CA happy. Heat and burps every now and then. Enjoy it!
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