Fridge repair - Page 1
Forum section: electronics / repair

author: akis
author_rank: Frequent Contributor
timestamp: May 19, 2016, 09:52:20 am
content: Fridge has issues. Control unit at the back and bottom, housed inside a plastic box. Cables from said box into the bowels of the fridge through two small holes that have been sealed with some sort of resin/glue/rubber grommet. No extra length on cables to allow the plastic box that houses the control unit to be pulled out and examined. It appears when the fridge was being assembled they pushed any extra length of cable inside the fridge (the space between the back and the inside) and then sealed the holes with this rubberized glue thingy.I cannot therefore pull the control unit out and pulling on the cables does not help, they must be glued inside the hidden fridge space very tight. The back of the fridge has been welded shut, no screws to take back covers off. Similar problem with cables inside the fridge and freezer compartments, they emerge from small holes into the back of the fridge, but there is no play, no extra length at all. It seems they fitted the fans, thermostats, console with lights etc, pushed extra cables into the holes, and then used some sort of glue/expanding foam to seal those holes.Any idea how to pull out the control unit out to carry out a repair? As a desperation (as I will throw the fridge otherwise) I can use wire cutters to cut the two cables as close as I can to the control unit, and then somehow reconnect them with extra lengths.

author: akis
author_rank: Frequent Contributor
timestamp: May 19, 2016, 11:49:23 am
content: I have cracked open the control unit enclosure and taken out the PCB. It is secured and clips in place with some plastic tabs and it is made of exceptionally thin and weak PCB that it has cracks along its edges that some propagate onto the tracks. I have thus repaired a few cracks. However the fridge is still not working properly so I will bin it.

author: Photon939
author_rank: Regular Contributor
timestamp: May 19, 2016, 03:11:40 pm
content: What purpose is the PCB serving? You could probably replace it with a mechanical device or MCU. Usual failures for a fridge are the compressor starting relay/capacitor/PTC and the defrost timer.You never did mention what part of the fridge isn't working.

author: SeanB
author_rank: Super Contributor
timestamp: May 19, 2016, 03:46:28 pm
content: Most likely the thermostat, with nthe fancy display on the front, along with the whizz bang flasy lights and swirling circles of colour.Ranco mechanical thermostat, coil up the sensing line on the back cold panel and away it will go for a few decades.

author: bitseeker
author_rank: Super Contributor
timestamp: May 19, 2016, 05:52:37 pm
content: Sounds a lot like the thermostat/defrost timer board. I've replaced the one in mine a couple of times during its 18 years and counting.

author: akis
author_rank: Frequent Contributor
timestamp: May 19, 2016, 05:59:31 pm
content: Fridge is working now even though the control unit is hanging out the back.The compressor/gas/etc is all good.The defrost heater I have no idea but it does not freeze up so I assume it works. Time will tell.The two thermostats, more accurately NTC resistors are OK. I had to chop out one and test it, it is OK, I will have to put it back (if I can get bothered) in in the meantime it uses two NTCs in parallel from my drawer, it's only a few Cs out of what it is expecting (for example it is -30C in the freezer and the MCU thinks it is like -22C, so I have set it to -20C and the motor, at last, stopped).The freezer fan was making a racket so I replaced it with a German fan and it is dead quiet now.The problem must have been loose connectors on the control board, I cannot think of anything else. I also repaired two cracked tracks on the PCB (PCB flexed and the tracks had cracks in them).

author: bitseeker
author_rank: Super Contributor
timestamp: May 19, 2016, 06:07:55 pm
content: Sounds like quite a thorough overhaul. Nice job.

author: madires
author_rank: Super Contributor
timestamp: May 19, 2016, 06:43:02 pm
content: A while ago I fixed a side-by-side fridge. The defrosting wasn't working correctly and at some point the cooling unit of the fridge side was completely covered by ice and needed a manual defrost. After the manual defrosting I checked the NTC, heater, fuses and so on. Nothing obvious. Several weeks later it happened again. Same procedure and still no clue. But that time I waited for the fridge to reach the set temperature and checked everything again. The defrost NTC suddenly had strange resistance values. So the control circuit thought the fridge didn't need any defrosting. A new NTC and the problem was fixed. My guess is that the frost/defrost cycles caused too much mechanical stress on the NTC (molded in some plastic for protection).

author: akis
author_rank: Frequent Contributor
timestamp: May 20, 2016, 10:18:45 am
content: Fridge is not working properly. It seems its control board is having issues. Freezer reaches -30C when it is set for -22C. Other times motor stops, stays stopped, temps increase in the fridge and if you open a door the motor instantly "wakes up" again. Display displays freezer temp as say 4C, of course wrong, reset the fridge and then instantly it jumps to -22C.I believe that the two NTS sensors are OK. The freezer one especially is mine - no issues with it misbehaving. The two fans also work properly. The heater element I am not sure. The heater overtemperature sensor, again not sure. The motor / compressor / gas - all fine. The door sensors are also fine.So the solution is to ditch the control unit and make my own using an Arduino Nano (it has an onboard USB and you can reach it with very long USB cables) controlling two relays: one for the motor and one for the heater. The rest is to write the right code. In addition the control unit has the voltage rectifiction on board - that will be trickier to achieve but I do have plenty of switch mode modules, at 12V, all I need is one of them and I should be running.My refrigeration technician friend said thjat fridges all contain MCUs these days and they misbehave (because it is software after all) and they monitor them with temperature recorders to see how the temperature varies over long periods of time, eg days!There was a very old, decades old joke about a King that had commissioned his people to make him a toaster. If you know that joke it seems that the OO software engineer was not thrown into the moat, but rather he designed the control unit of my fridge!

author: madires
author_rank: Super Contributor
timestamp: May 20, 2016, 12:01:46 pm
content: I had that funny business with the temperatures too. Is the cooling unit of the fridge (evaporator) completely covered by thick ice? You can check the heater with a resistance measurement. There might be a temperature fuse to prevent overheating.You can find lots of "how to fix my fridge" videos on youtube. BTW, most of the side-by-side fridges got a hidden service menu where you can adjust temperature offsets or run the defrosting manually.

author: CJay
author_rank: Super Contributor
timestamp: May 20, 2016, 01:02:08 pm
content: Quote from: akis on May 19, 2016, 09:52:20 amPlenty of electronically controlled fridges have issues with the drain holes becoming blocked and the temperature sensor getting damaged by the accumulation of condensed water, it causes them to defrost or ice up excessively.Well worth checking the drain holes and for corrosion around the cabling that runs close to them.