Problem with fridge compressor - Page 1
Forum section: electronics / repair

author: alah
author_rank: Contributor
timestamp: March 16, 2018, 07:40:50 pm
content: I have a fridge compressor 1/3 HP ( on my benchtop ; really my desktop ) so the tubes are not connected to anything, not even the service valve. When I apply power it starts humming, trembling so I think it running. After a minute or less the thermal overload activates and when I measure the current its about 12 Amps. Could the fault be due to the open tubing or the compressor windings are shorted? I really wouldn’t like to believe the last so I would appreciate it if a few of you could confirm; THANKS, Alberto.

author: orion242
author_rank: Unknown
timestamp: March 16, 2018, 07:52:46 pm
content: Its probably not going to be happy open to the atmosphere. Most of these are cooled by refrigerant, which is not the case anymore with this one. They also require lubrication which if this was left open and on its side / upside down, could have all leaked out.

author: hermit
author_rank: Frequent Contributor
timestamp: March 16, 2018, 08:48:26 pm
content: The relay may not be dropping out the start windings. But, you've sucked moisture into the oil so the thing pretty useless as is. If the relay is the problem you could try changing the oil. This depends on what you want to use it for though. The work involved vs the failure possibility quotient is up to you.

author: Armadillo
author_rank: Super Contributor
timestamp: March 16, 2018, 08:58:47 pm
content: Replace the AC capacitors and try again.

author: Seekonk
author_rank: Super Contributor
timestamp: March 16, 2018, 09:32:09 pm
content: Give up, it's dead. You have probably locked the rotor from moisture. You still have one chance. The start winding likely goes to a PTC resistive element. That could be open. Applying power and shorting it out for a second should start it. If not, it's toast.

author: jmelson
author_rank: Super Contributor
timestamp: March 16, 2018, 09:35:17 pm
content: Quote from: alah on March 16, 2018, 07:40:50 pmDo you have the starting relay? These generally have 3 terminals and a thermally-operated starting relay. The line is connected to both the run and start winding when power is first applied. After a few seconds, the thermal device heats up and disconnects the start winding.Jon

author: james_s
author_rank: Super Contributor
timestamp: March 18, 2018, 06:13:55 pm
content: I've seen failed PTC starters on a number of compressors.Many fridge compressors will seize due to moisture if they sit open to air though, the internal assembly is made of iron and rusts readily. If you run them regularly they can make reasonable utility compressors or basic vacuum pumps though.Once you are sure it's seized, it's sometimes possible to cut the top off the dome and free it up, I've done that on a couple of occasions and it still works to compress air as it's the input that is open to the inside of the dome.

author: alah
author_rank: Contributor
timestamp: March 22, 2018, 07:17:26 pm
content: Excuse me for my late reply; I dont have internet at home; THANKS for your answers. I thnk that james S answer is reasonable; this was left with the tubes open for quite some time so I would believe its seized. Its a 100vv compressor, what do you think about trying to start it with 220v?

author: james_s
author_rank: Super Contributor
timestamp: March 22, 2018, 10:28:11 pm
content: If you're going to throw it away otherwise then I suppose you have nothing to lose, but past experience suggests that is not likely to succeed. I freed up a couple of seized fridge compressors and it required soaking in penetrating oil and working it loose by hand after cutting around the weld to lift off the top of the dome.It's kind of fun to open those things up, they're quite remarkable contraptions. Especially when you think of how many refrigerators run for 30+ years, most get replaced due to cosmetic issues or things like broken shelves and door seals rather than problems with the hermetic system. Also you cut open a crusty 30 year old compressor and it looks shiny brand new inside.

author: vaualbus
author_rank: Frequent Contributor
timestamp: March 22, 2018, 10:54:28 pm
content: I don't think this is the right site for your question.lately this seem to became a general forum and no more related to eletronics.To be clear I'm no criticize you, I'm just saying that you could get more help in other sites.

author: SparkyFX
author_rank: Frequent Contributor
timestamp: March 23, 2018, 02:14:03 am
content: Well, i would second hermits suggestion that the starterwindings(correction) capacitor might not be dropped, that explains why it is running but then shutting off due to overtemperature. Some single phase induction motors have a centrifugal switch on their shaft to achieve that. Broken pistons and cylinders can easily be identified based on how that compressor sounds.Also the refrigerant usually also contains a lubricant oil, which emulsifies while in operation and separates when standing still. As long as the compressor is the lowest point in the system it will be oil filled at the time of disassembly.If a question regarding electrical applications is in the right place or not is a thing of the personal vantage point. Mine is that electronics usually are not self-sufficient and therefore also do control loads. Understanding these loads, how they work, how they may fail is as crucial to a good electronics engineering as the control itself. The electrical principles apply in the same way they would apply to any other part of a circuit. It would be like saying that e.g. questions regarding switches are not in this domain as they are mechanical devices, yet an EE can spend days on how to properly debounce it.

author: james_s
author_rank: Super Contributor
timestamp: March 23, 2018, 03:03:50 am
content: Electrical Engineering comprises much more than just electronics specifically, and a refrigeration compressor is certainly electrical.These compressors have a clever method of lubrication. It does circulate through the system but there's also a pool in the bottom of the can, there's a spiral milled into the shaft which causes oil to be pumped up to the top end where it is flung outward and drips down over the whole compressor assembly.

author: SparkyFX
author_rank: Frequent Contributor
timestamp: March 23, 2018, 04:44:59 pm
content: Sorry for getting off topic: As far as i understand it, people working in electronics always have the electrical education included, or am i wrong with that assumption? Not saying they are all certified electricians, of course.

author: hermit
author_rank: Frequent Contributor
timestamp: March 23, 2018, 04:51:51 pm
content: Wanna drop programming discussions too?

author: james_s
author_rank: Super Contributor
timestamp: March 24, 2018, 05:25:17 pm
content: So long as it's related to electronics I have no issue with programming discussions.

author: Crazy_Engineer
author_rank: Contributor
timestamp: March 25, 2018, 11:46:41 am
content: Although I have not worked on fridge compressors before, my experience with AC motors makes it sound like the start capacitor needs to be changed out. With a bad starting capacitor, the motor will make a little noise as it tries to start up, but cant. Then it will rapidly get warm as the stall current flows through it. 12A is about the stall current you would expect on a 1/4 hp 120V motor.

author: hermit
author_rank: Frequent Contributor
timestamp: March 25, 2018, 03:25:22 pm
content: Quote from: Crazy_Engineer on March 25, 2018, 11:46:41 amNot all motors use start capacitors. Many of the new compressors in the states use run capacitors.

author: james_s
author_rank: Super Contributor
timestamp: March 25, 2018, 04:27:43 pm
content: Most fridges I've worked on have no capacitor at all, just either a current relay or more recently a PTC. Air conditioners commonly use a PSC motor, permanent split capacitor which have the run cap you mention. Maybe it's used in fridges now too, I don't know, either way a bad capacitor will cause the same symptom but I doubt that's the issue here.

author: SeanB
author_rank: Super Contributor
timestamp: March 25, 2018, 05:10:15 pm
content: Yes most small fridge compressors use a PTC starter, replacing the older current operated start switch. The 2 are designed to be interchanged, and you can have a start capacitor with the PTC or the current switch starter, which also provides overload protection, but almost no fridge freezer compressor will have one, they rely on the cap tube system equalising pressure between cycles so the compressor starts with low load.If it was from a unit with R12 it would have had mineral oil as lubricant, but if it was used on R134A, R600 or other refrigerants the oil would have been POE, which is hygroscopic and which turns into acid when exposed to moisture, rusting the compressor internally.

author: tmbinc
author_rank: Frequent Contributor
timestamp: March 26, 2018, 07:08:15 am
content: Sorry for the meta-discussion, but I for myself find it great to have these repair discussions in this forum. You get a lot higher quality background information than on the generic "fridge repair" forums.For example, the most awesome discussion I've ever found was on mikrocontroller.net (a german discussion forum about .. microcontrollers, I guess; not very different from this forum), where someone tried to repair an old dishwasher with broken electronics. On most boards discussing "white goods repair", you'd mostly get the part-nr to replace. However that guy didn't want to hand-wash for so long and needed the dishwasher to work, so based on a timing diagram he was given he built a replacement dishwasher controller in just a few days. (Here is the - german - thread:https://www.mikrocontroller.net/topic/93765but you should still be able to see the pictures).

author: Crazy_Engineer
author_rank: Contributor
timestamp: March 26, 2018, 03:17:05 pm
content: Quote from: SeanB on March 25, 2018, 05:10:15 pmThat was very informative.My previous experience is rather limited as it has only consists of sprinkler pumps and an air conditioning compressor unit.You, on the other hand sound like you professionally repair fridges.

author: alah
author_rank: Contributor
timestamp: April 02, 2018, 08:06:22 pm
content: Sorry about any fuss; no hard feelings, anyway. We at Venezuela NEED to fixEVERYTHING. This comressor would cost one years salary but when you save that amount the price could be tripled!I do like opening apparatus and fiddling with them, but not without at least some idea. Ill open it tomorrow and let you know by Wednesday. THANKs, Alberto.

author: alah
author_rank: Contributor
timestamp: April 10, 2018, 08:07:09 pm
content: Back again. I opened the unit and, what a beauty. Didnt see any signs of rust, the windings are shiny as new. I emptied the oil and after a few day noticed dirt an a bit of rusty like material. the shaft was stuck but I freed it with my vise grip and could turn it by hand. So I powered it and now it runs fine; just 3 Amps. as Techuseh technical data states. It is short of poi though, only had a bit more than the 480ml stated.So, THANKS a lot for your help; You almost saved somebody¨s life.

author: james_s
author_rank: Super Contributor
timestamp: April 10, 2018, 09:56:10 pm
content: Nice job. If you weld the top back on I recommend flooding it with an inert gas like nitrogen or argon, otherwise you could ignite oil vapors and have an explosion. Be careful.

author: alah
author_rank: Contributor
timestamp: April 13, 2018, 07:28:45 pm
content: Quote from: james_s on April 10, 2018, 09:56:10 pmI suppose thats because the residual mineral oil is combustible?Do you meansprayingthe inside with nitrogen before I start welding orduringthe welding process?The compressor is consuming 3 Amps without the top; shouldnt it be less? I suppose it will consume more if installed, with refrigerant.Just in case, if I need to withdraw the unit from the can, even though I have a video, I cant see how to free the angles with the springs thathold the unit in place. Am I supposed to force themupwardswith screwdrivers? Thanks.

author: james_s
author_rank: Super Contributor
timestamp: April 13, 2018, 08:27:53 pm
content: Typically you would connect the intake line to a low pressure source of inert gas and leave it running at a low rate throughout the welding process. I don't know if the oil vapor you have is combustible or not but I would be careful in case it is. You should be able to use the same type of gas that is used as shielding by the welder.I also don't know how much current it should draw but 3A doesn't sound all that crazy. Does it rotate freely by hand? The way the springs attach depend on the unit, I don't think there is any standard. I've never taken one that far apart that I planned on putting back together.

author: alah
author_rank: Contributor
timestamp: June 12, 2018, 02:14:25 pm
content: Thanks, I´ll weld it back and test; will report back.

author: tpowell1830
author_rank: Frequent Contributor
timestamp: June 12, 2018, 02:58:52 pm
content: Quote from: alah on April 13, 2018, 07:28:45 pmInductive motors like that will run at constant current due to slip. You should not see much more than 3 amps when it is loaded, otherwise it will stall if you overload it, and then you would see stall current (12 amps as seen before).Hope this helps...