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Redbull Mini Fridge Compressor cycles every few minutes

haku

Premium Member
Joined
May 12, 2017
Messages
3
Location
Washington
Model Number
redbull
Brand
-major brand-
Age
Less than 1 year
Hello

I have a redbull mini fridge that stopped running, and sat for a few months. Initially I thought it was the PTC, overload relay, or compressor itself.


1. PTC: no rattling sound, burnt smell, and there is continuity between the 2 holes (circled in red), and continuity between each hole and the tab circled in green.
-I assume this means PTC Is ok?
http://i.imgur.com/lrFo54x.jpg

2. Overload: has rattling sound when you shake it. has continuity between the large metal part circled in green and the tab circled in red
http://i.imgur.com/dhyT2mo.jpg
3. Compressor pins
-~24 ohms between the lower 2 pins
-14 ohms between lower left pin and top pin
-11 ohms between lower right pin and top pin
-there are no shorts
-I read that since the values add up to ~24 ohms, it means compressor is okay?
http://i.imgur.com/dWAlODA.jpg
-I did notice a ton of oxidation, leaks (see pic)


Anyway, so I thought everything above was Okay as above.

The temperature control is adjusted in the back, it's attached to a PCB board. I noticed that the starter relay on the PCB would engaged when powered, it also rattled. So I replaced the relay on the PCB. I also replaced a slightly bulged capacitor on the PCB board as well.

I plugged it in and it fried up!

The fridge itself can cool down to 1-5 degree Celsius depending on the temperature dial.


However the compressor runs for 2 minutes, then off for 5 mins, and repeat this over and over. The compressor is quite hot to touch.


I only let it run for a few hours as I thought the compressor cycling was too frequently.


Sorry for such a long post, but does anyone know why it would be cycling so frequently?
I am thinking is it the capacitor overload (ohms okay i think?), or is the compressor bad/low in freon (due to the oxidation/leaks?!)


thanks a ton!
 

rickgburton

Appliance Tech - Moderator
Staff member
Joined
Jul 11, 2006
Messages
44,788
Location
Murray, Utah 84107, United States
Unfortunately I can't find any information on that unit and I have no idea what the specs are. I don't know anything about a "redbull" machine. Here's what I do know however. The compressor was replaced and the corrosion on the lines is from brazing flux that wasn't cleaned off. It can cause a leak but there's other issues I see. For one, those resistance measurements seem awfully high. Every compressor I've seen the start windings should be 3 to 11 ohms and the run windings, 1 to 5 ohms. The PTC Relay should have 3 to 16 ohms between the two holes. My question to you is did this problem just start and was the machine working right before the short cycling? It sounds like the compressor is too big, too many BTU's or larger Hp. If the compressor is too big for the application, it short cycles and causes the compressor to run hot. Is this a vending machine? Cubic ft?
 

haku

Premium Member
Joined
May 12, 2017
Messages
3
Location
Washington
Hi

Thanks for your reply. The fridge is a small mini fridge, used to store drinks (about 2 dozen cans or so?), it was used in an office setting and just 'stopped working', so it was left to sit for a few months.

Here are the specs of the fridge: http://imgur.com/UfpM37t


As you can see it's only 0.7cu feet!

I retested the pins on the compressor using this video here and the meter set to 200 ohms.
-Red probe to top pin and black probe to bottom right: ~9 ohms
-Red probe to top pin and black probe to bottom left: ~13 ohms
-Red probe to bottom right, b lack probe to bottom left: ~23 ohm

PTC: 5 ohms (between the 2 holes), so that's probably not it.

I am not sure if the compressor was replaced because there is still sticker on it that states the model # (you can see it in the picture here: http://i.imgur.com/dWAlODA.jpg)


So perhaps the compressor is bad if the ohms are so high on it (unless im measuring it incorrectly)
 

rickgburton

Appliance Tech - Moderator
Staff member
Joined
Jul 11, 2006
Messages
44,788
Location
Murray, Utah 84107, United States
Whatever is the lowest ohms scale on your meter is where you want it. You're only measuring a few ohms. When measuring ohms it doesn't matter which test lead goes where. You'll get the same measurement even if you switched them around. The compressor may not have been replaced but the system was opened. The flux is a dead giveaway so is the end of the process tube. It may have had a problem like a refrigerant leak and a service valve was added to the process tube. The other lines probably were not disconnected but when the service valve was removed and the process tube sealed, they may have heated the other joints and melted the weld for a reseal for good luck. Whenever a sealed system is opened the filter/drier must be replaced. The filter drier is the fat piece with the capillary coming out of the end and wrapped around it. That one is the original drier and was never replaced. These are factory welds:
factory welds.jpg


0.7 cubic feet is small and it only uses 1.1 oz of R134a so two minutes running may be correct if the door is closed and it's not getting much use. I don't think it's short cycling but the compressor is bad. The PTC is good. The windings resistance is too high. You measured 14 ohms the first time and 13 ohms the second time for the start windings. Normal is between 3 and 11 ohms. For the run windings normal is 1 to 5 ohms. You got 11 the first time and 9 the second time (That's twice as many ohms as it should be). It's not necessary to measure the resistance between the two bottom pins. That the combination of both start and run windings. So, more resistance means more current and more current means more heat. The reason the compressor is hot. Sorry for the bad news.
 

haku

Premium Member
Joined
May 12, 2017
Messages
3
Location
Washington
Thanks for the information. I am guessing if the compressor is bad, that's what caused the relays on the PCB to blow.

I wonder why the ohms read high? perhaps mechanical issues causing higher resistance?
 

rickgburton

Appliance Tech - Moderator
Staff member
Joined
Jul 11, 2006
Messages
44,788
Location
Murray, Utah 84107, United States
There's an insulation on the windings that starts to break down and when mixed with the R13a refringerant changes the chemical composition. Any contaminate including moisture in the system will do the same thing. Once that starts it progresses fast and the compressor draws more amps to start and run. More amps = more heat. More heat causes the insulation to break down even more and that causes more resistance in the windings
 
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