Replacing changing repair troubleshooting fault finding , fridge freezer or refrigerator , compressor , thermostat , relay , overload cut out , gas top up
When working on these system safety is the first priority. R600a is a flammable gas and precautions should be used when working on these systems, they do not hold much aprox 80 grams but still be careful when using and storing. Keep the room well ventilated when working on these systems and remember butane will settle to the bottom of a room being heavier that air.
If you suspect a problem with the system you can attach the gauge to take readings of the gases pressure to help with fault finding diagnostics.
Healthy systems can have a static pressure reading of between 0.5 - 3 bar , that is with compressor off and pressure equalised from low to high.
With the gauge connected to low side and compressor turned on you would expect to see pressures between -0.1 and -0.6 , negative because your on low ( suction ) side of compressor.
If when you turn on compressor the gauge does not drop into the negative this is a sign your compressor is faulty.
If the system pulls into a complete vacuum it could be a sign of the system having a blockage somewhere if it goes below -0.6 slightly its worth adding a tiny squirt of gas but more than likely the drier unit has become blocked. ( replace drier unit , vacuum system and recharge.)
If you suspect a leak you can use an electronic sniffer to find R600a leaks quite easily, remember to turn compressor off for testing low side of the system and to turn compressor on for high side testing..
After you have vacuumed down the system and ensured its free of contaminants and moisture and leaks ( by allowing for enough vacuum time )
You gauges will still be attached to the low pressure line from vacuum down.
Attach the bottle of gas to the vacuum fill hose of the manifold gauge and ensure the gauges are zeroed
open the bottle this will fill the hose , undo hose connection and purge the air form the hose so you do not put any air into the system.
You now need to open the tap to allow refrigerant into the low pressure side of the system, allow in a few grams of refrigerant and turn on the compressor. This will allow the compressor to draw in the refrigerant and circulate the vapour. Using your scales now add the exact amount needed to refill the system.
to finish shut of bottle valve and allow compressor to draw in refrigerant left inside the hose, once this is done turn off the valve to disconnect system from the manifold gauges.
Low side pressure on a healthy system is usually between 0.1 and 0.6 bar.
An excellent video refilling with liquid refilling upside down bottle.
fridge compressor change , Vulkan Lokring demonstration and recharging
Vacuuming the system down is perhaps the most important step of the repair process.
Firstly the negative pressure you put the system under can be used to check for leaks and you clean out all the air , moisture etc from out of the system and being under negative pressure the moisture in the system will be boiled off as well .
Make sure you ensure all pipe hoses and connection on your tools are tight nothing worse than chasing leaks to find its your equipment.
With the manifold gauge connected to the system via the inline Schrader valve tap on the low side, turn the pump on and open the valve connecting vacuum pump to circuit. you should here the note of pump change and sometime you will see mist come out of the pumps breathing port as moisture it burned off.
You should vacuum down for at least 20 minutes to burn off moisture you should then shut the vacuum pump off and allow the system to hold its negative pressure for another 20 minutes.
The main gauge will be at minus 30 psi but it can be hard to spot leaks on this so it best to use a more powerful gauge, the vacuum pump I own has a very sensitive gauge and it will easy show up even the most minor of leaks so a always not and watch the reading of both.
If it holds for 20 minutes your fine to regas if not you need to find the leak.
I use the single gauge manifold as below its been excellent for my uses I use it for system testing refill through it and vacuum down.
The gauge is used to measure the pressure in the system ( low side ) suction, in PSI or bar if you have the correct gauge for the gas being used the temperature scale can be used to find the evaporator temperatures at certain pressure to aid in diagnostics. But this gauge it mainly used by me for checking gas pressures and good operation of the compressor.
When putting the system under a vacuum i use the gauge on my vacuum pump this reads in milibar and is much more sensitive to pressure changes and even very minor leaks can be found. Well worth checking as ive gone to customers houses after other techs and found minor leaks that shut the fridge freezer down again weeks or a couple of months after.
The gauges when connected give a reading instantly the on off tap only opens the valve to the centre valve for topping up or vacuuming down purposes.
See photo below to help visualise this , the gauges will always read pressure measurement.
Removable line tap type Schrader valve , look for the best place to fit one on the pipe work most of these valve fit to 6mm to 8mm copper pipe. I would recommend you measure this first as if it does not fit your in a bit of a mess.
Ensure the collar is an exact tight fit to the pipe work , bent or misshaped piping can cause leakage.
Assemble the valve around the collars on the pipework and tighten the two clamping screws / bolts
Wind down with equal turns on each side to prevent damage to pipe and an equal seal all round do not over tighten as to damage or misshape the pipework.
Once in place tight enough for its purpose and your happy everything looks good you can now pierce the pipe , to do this you screw the cap on with the plunger fitted this then pushes the pipe piercing tool into pipe
Sometimes it may not be possible to fit the line tap version and you need to fit a fixed Schrader valve to the charging port on the compressor.
lokring Schrader
Before cutting the pipe prepare the surfaces as it is easier emery cloth the out side and make it clean, paint free and smooth.
Measure the pipe before cutting and ensure you have the correct sized lokring.
When you have cut the pipe work prepare the surfaces more for the joint. Apply some prep fluid to clean the surfaces. Fully insert both pipes ends into the lokring and use the lokring tool to tighten the fitting onto the pipework.
Remember R600a in flammable so this type of cold pipe working is preferred as to the older braising at high heat. But they can be very expensive especially when fitting a new compressor with all the connections and then to regas system it can work out too costly for some.
Usually found on high end units, it freezes ice cubes ready for appliance owners when needed. it will be located in the freezer unit to take advantage of the freezing temperatures.
These units need to be connected to the cold water mains connection in order for the ice to be renewed.
The temps in the ice make are monitors by an NTC sensor and when the ice is required a motor with turn the tray to free the ice up ready for dropping into the glass required. An arm on the front of the ice maker makes sure that the ice does not overfill .
These unit usually have a test button on them so they can be tested when needed, its a common failure to see the tray snap from the maker this would water to spill over the food in the unit so is usually spotted quite quickly.
You could get a motor failure or a failure in the control side of the system so test for power at the motor prior to replacing and ohm test the motor to see if it is faulty as well. If the arm that stops the ice maker broke it could continuously make ice even when not needed this can be a costly fault so keep an eye out for damage.
Test motor for ohms resistance reading 40 ohms for smaller motors , Test the micro switches , Test any fans for ohms and then test the NTC for ohms reading , ensure no shorts in the parts and look after service information on your model to check ohms readings.
Fridge freezer ice buckets
Ice from the ice maker is dropped into the these ice buckets and it then can be used to dispense the ice cubes to the appliance user. To dispense the ice a motor and large screw auger is used the motor turns the auger and the auger pulls the ice towards the exit. other than the screw failing or coming lose the only other problems could be freezing up or the motor failing. Sometimes there may be a solenoid fitted this is a switch to prevent crushing of the ice so either full cubes or crushed ice can be selected by user.
To test the motor take an ohms reading and match this to service specs for appliance make sure there are no shorts or earth leakage currents by testing for continuity.
Same thing for the solenoid if one is fitted
The plastic bucket can weaken and crack over time if so replace it.
Its worth noting that certain fridges are not going to function correctly out of there climate class for example most UK fridges are class N which means they are suitable for +16c to +32c , if the temps start to go above 32degrees Celsius then the condenser may struggle to lose its heat and the refrigeration cycle will be affected. Bear this is mind as it may be a problem in very hot spells or in the unit is fitted somewhere to hot for example a conservatory or in a kitchen with constant heat. So if you come across a recently moved or new appliance not functioning it may be because of the environment it is located.
Defrost heaters are fitted to units with automatic defrost systems they use a timer mechanical for older fridge freezer units and digitally controlled for more modern machines.
The heating element is just the same as any oven element.
A resistive element is encased in a insulated material and then surrounded by an outer metal protective casing.
Elements can fail and usually fail open circuit or Ol on the meter if intact you can work out the ohms reading by the wattage of the element and the volt with ohms law. With these elements is always good practice to insulation resistance test them to check for earth leakage currents.
These element need a timer to turn off and some sort of control be it a thermostat or a digital sensor. There is usually some sort of thermal cut out protection and a thermal cut out fuse is used to disconnect power if the device should overheat.
Thermal cut out fuses can be tested for continuity and replaced if blown remember to check for any reason the fuse blown maybe insulation resistance of element has failed or water ingress always best to check. When replacing the fuse make sure you fit it exactly where it was before to prevent nuisance tripping.
Old units will use a mechanical timer to turn the defrost element on-off today electronic programming is used.
Visually check to see timer operation to confirm its working or not if its not or its getting noisy in operation them replacement is only option.
Modern or high end fridge freezer units often use fans some for circulation of the cold air from the freezer cavity to other cavities such as the fridge. There may also be cooling fans on a compact condenser as well to aid cooling of the refrigerant.
Fans will have motors to drive them on modern newer fridge freezers the motors are usually DC motors older fridge freezers used mainly AC motors so understanding both is a must when it comes to testing and fault finding.
AC motor generally used are shaded pole types which are usually very reliable , they are self starting, single phase induction motors. you can measure the windings of these to ensure they are intact otherwise it could be a bearing or the mechanical side of the fan that is at fault like a blockage or frozen solid . resistance reading are usually 800-900 ohms or thereabouts.
DC motors are usually BLDC brushless motors these need a speed sensor usually a hall effect sensor to now where in the rotation the rotor is so timing of rotating magnetic field can be controlled. The control is usually done buy a electronic motor drive board where speed and rotation can be controlled. Again these can be subject to mechanical fault and freezing solid , you can ohm test the coil windings and the sensors but its hard to locate and test the motor drive PCB.
This is used in more expensive models where a secondary evaporator is used to cool a second fridge freezer cavity, when the temperature reach a set point then the diverter valve with operate and allow refrigerant to flow to the second evaporator as well.
These valve use either synchronous motors or just a simple solenoid valve to open them when they are signalled.
What can go wrong with diverter valves
If the secondary fridge freezer cavity is not getting cooled but the primary is functioning ok then its a god sign the diverter valve may be faulty and its best to test it prior to replacing any parts as it could be a control issue and not a faulty valve, normally the fridges with these are fitted with self diagnostics and servicing modes where you can manually operate the valve to ensure all control function are fine.
Study up on the model your working on and see what information is available on the service modes and diagnostics.
The solenoid valves have a coil of wire and are easy to test just take a resistance measurement over the two terminals. Reading can be from 1-4 ohms but if you get Ol then the winding in damaged and needs replacement. Replacement means recovering and recharge of the system.
These are used where 2 or more compartments are cooled from one evaporator, it gives a degree of temperature control.
The refrigeration system will be used to cool the freezer department and the air from the freezer used to cool other compartments usually with the aid of a circulation fan. When the baffle is signalled to open the fan will blow cold air into the secondary department and warm air rises to be cooled in the primary cavity.
Baffle are electro mechanical and require a signal from a temperature monitoring device and the associated sensors and electronics to provide control, some older units use a bellows type diagram that opens/close the baffles when a temperature is reached.
The electric baffles use a small synchronous motor to move the baffle usually a reed or micro switch is fitted to tell the controller what position the baffle is in.
What can go wrong with these baffles
If the primary unit is working fine and is freezing the cavity as normal then its a sign that the cool air in not getting into the secondary compartment for some reason, it could be a over freezing and a blockage, fan failure , or the baffle door could be frozen solid so confirm the parts are faulty before replacing do some test checks and inspections. If the fridge is getting too cold then the baffle door could be cracked or even frozen in the open position.
You can test the baffles motor for ohms with a multimeter if it tests OL it means the internal winding is damaged and you need to replace. Test the micro or reed switch as the same time to ensure continuity.
The condenser is directly after the compressor in the circuit the super heated vapour from the compressor goes though the condenser. The job of the condenser is to get rid of the absorbed heat and cool the vapour enough to condense it back into a liquid again. The condenser has lots of fins on it to increase its surface area to remove the heat efficiently on some units it may be compact and use a fan to blow air over it to aid in the heat loss.
The input side of the condenser is the compressors high pressure side outlet and the outlet of the condenser goes to the filter drier and capillary tube.
Condensers are usually located at the rear of the fridge freezer unit but can be compact and at the bottom of the unit these typically use a fan to aid in the heat loss process.
What can go wrong with condensers
The condenser must be able to give of its heat if it is covered over or the fridge freezer is fitted somewhere to hot then this will affect the efficiency of the refrigeration cycle and could lead to issues with bad food with too low cooling temperatures. If the fan fails on the compact versions this will affect the refrigeration cycle too and affect cooling in the fridge freezer cavity.
Check the condenser when servicing and ensure it is clean and free of any hair fluff or debris and make sure no damage has occurred to it during installation or with dropping things behind the appliance.
The high pressure liquid hit from the condenser travels through the small diameter capillary tube it then hit the larger diameter of the evaporator which causes the high pressure liquid to change to a low pressure gas as it passes into the evaporator. The expansion of the liquid to gas causes the temperature to drop and to cool the evaporator. Air passing over the evaporator is cooled and gradually the temperature inside the fridge freezer cavity will drop.
Its normal to see the evaporator covered in a layer of frost so this is no an issue.
The evaporator has fins all over it to maximise surface area and to aid in heat absorption.
Not much can go wrong but over time the constant cooling and warming cycles and associated expansion and contraction of the metals can cause leaks to occur. Its a regular thing to see damage to the evaporators after DIY attempts to speed up the defrosting.
These are small items but essential for correct operation, they have 2 main functions. Filtration and to absorb any moisture and contamination in the system from the initial gas filling.
Silica beads inside the unit absorb any moisture as it passes though the receiver drier and filter out any foreign body's in the refrigerant in a built in mesh on each end of the unit.
The capillary on a fridge is only 1mm wide so its a must to have a drier filter fitted to prevent blockages of the capillary.
What can go wrong with these
If the mesh wears and splits this can allow particles to pass and if the silica beads become saturated they will no longer absorb moisture. They can also become blocked and prevent easy passage of refrigerant as well if anything is suspected to be wrong with the drier you will need to replace which entails braising in a new on and recovery and charging on the system.
So what can go wrong with compressors , well they can a do fail they can fail electrically and mechanically but sometimes the control side of things can fail so ensure you are 100% correct when condemning and replacing a compressor as they are expensive and difficult to replace.
The pistons in these compressor sit in a bath of oil that what makes them so reliable obviously a loss of oil would cause failure quite rapidly even seizure of the entire compressor. A seized compressor can still be attempting to start and this can be heard as a clicking this is the relay and overload protection attempting to start the compressor then cutting out when it cannot and it shuts power off.
Over time seals can wear and reduce the pumps efficiency sometimes you can tap on a compressor and it will alter the pressure reading this is a symptom of bad seals.
Windings can fail open or shorted so measuring these correctly depending on the type of compressor is very important. When testing a normal compressor the 2 start run winding reading should equal the final measurement. when testing invertor winding they all should be equal and the LG linear invertor compressor only has one measurable winding between 4-9 ohms.
Found on more modern or top of the range LG fridge freezer units , these we developed for efficiency they all still do the same job that is pump refrigerant around the system. Normal compressors use a 4 step process but these do the same motion in one singular motion this reduces wear, tear, friction, uses less energy and is quieter in operation.
The compressor is controlled by the invertor which provides voltage at between 30v and 440v varying the speed of the compressor motor to do this a doubling capacitor is used.
To test these you need to test the capacitor see our post here on that. A sign of these failing would be very slow compressor with poor cooling in fridge freezer.
The pins look similar on these but it only has one winding so you should only get one reading from these between common and run and can be anything 4 - 9 ohms. You really need to insulation resistance test for these too to earth.
All appliances that need temperature regulation need some way of sensing the temperature inside the cavity that is being used.
In the case of fridges 2 main types are used, electro mechanic bellows type thermostats and thermistor digital NTC sensors.
The bellows electro-mechanical type
Have been used the most over the years as they are cheap and reliable but they are not the most accurate and the control is basically an on and off switch. It operates by the principle of expansion of gases. As the temperature around the phial changes the gas contracts and expands, this movement is use to turn the switch on or off . There is a dial usually numbered 1 to 5 this can be used to alter the distance between the contacts and therefor it will to a certain level of accuracy give less or more cooling time to control the temperatures in the cooled cavity.
The phial of the thermostat must be located on the evaporator to sense the temp this is why buying the exact OEM replacement is wise as some universal ones can be too short and as such would not be in the correct position to read temperature and this would affect cooling seriously. ( remember if its a few degrees out then food could become poisoned )
What can go wrong with these, they are quite reliable but as mentioned before they can be too small if you buy cheap replacement, they could be designed internally for differing temperature ranges , the phial/capillary itself could develop a leak and lose its gas which would mean over freezing as compressor would not turn off.
It could also fail in the open position and not run at all see above post for multimeter tests, if you know what your doing and only if you know you could jump the wires to see if compressor switches on , you need to connect the live to the switched live only for a very short time but beware you could cause damage or injury so only attempt if you know what you are doing.
Digital thermistor temperature sensor ( NTC )
Most modern and top of the range fridge freezer units now use a digital method of sensing the temperatures these use the thermistor NTC type sensor.
The sensors monitor the fridge freezers cavity and feedback to the control board the temperatures, there can also be other sensors for defrost and outside temperatures and sensors for different compartments. This is so the control board can have all the information needed to control the refrigeration cycle accurately.
NTC negative temperature coefficient as temp rises the resistance falls, this can be used in the testing process.
To test you need the multimeter as the sensors use resistance you will need to set the meter to read ohms. Take a measurement at room temperature and compare this again manufacturer specifications you can then cup your hand around sensor to warm it up at it should if working correctly drop in resistance.
What can go wrong with these sensors, They can go open circuit internally or in the wiring, this can be confirmed by using the multimeter set to resistance and take an ohm reading it could also create an error code to flash up on the fridge freezers display panel.
Sometime the insulation can break down around the sensor and water can get inside this will make the sensor read erroneous measurements and will then affect the cooling of fridge.
Replacement is the only option with these and they are no expensive anyway but always buy OEM
Video below shows process of testing both thermostats and digital temperature sensors thermistors
With electronic digital control the electronics boards have built in self diagnostics programs, these monitor system operation and flash a code up if any malfunctions in these systems occur.
If you need a code then search the manufacturers website and you will find all the error codes and there meanings. Some basic codes may be found in your instruction manuals as well so might be worth reading.
Its always worth googling if you cannot find information on the manufacturers websites.
Treat codes as a guide as its rare they will pin point the exact fault but can often give you a direction to go in with your fault finding.
Most modern and in particular higher end models use digital control and temperature sensors to more precisely and efficiently control the cooling cavity. The PCB is the electronics board where all the input and out put connections of the control system go and when the programming software it containing.
The PCB with monitor temperature within the fridge freezer cavity and will turn the refrigeration system on and off to maintain the correct set temperature.
Most PCB digitally controlled fridge freezer units have a built in error code list which can help in fault finding diagnostics.
The PCB is the main part of the system and is an electronic centre that controls the temperatures of the fridge with more precision as compared to the older on-off electro-mechanical thermostats. The PCB monitors the inputs ie Thermistor inside fridge cavity controls the output ie compressor on off and power in linear compressors to keep the desired temperature in the fridge freezer.
You can test a lot of the components on a PCB as they are mostly simple electrical components for when it comes to control and program chips these are not rally replaceable.
When a PCB fails it can be anything from a single function failing to complete system failure and no lights or functioning, it could trip the electric or RCD or it could flash up a code so a lot of fault finding can be needed to call the expensive PCB as the fault.
PCBs can have single component failure or a track on the board have open circuited.
Common symptoms of a PCB failure are No power , NO cooling , error codes and not carrying out a specific function.
Test for power coming into the PCB , check for any fuses as well. You can also test the relays or bypass them by removing the outlet side terminals and jumping them to see if the oven elements now operate.
Sometimes heat or water can damage a PCB board and timer will need replacing but you may need to look for the cause of heat or water.
Above is a basic timer PCB all components can be tested and replaced with a little know how, see video below for basics of component testing.
Testing electronic components with a multimeter ( Basics )
Testing basic electronic components, i use an electronics learning board to practice testing i recommend getting one if your a beginner here i show you some testing on the learning board and real components.
First ill start with resistances on the learning board here is a photo of all the resistances on this board from 100 ohms to 0.470 M ohms.
So set your meter up to read ohms on the selector dial and the leads in correct terminals.
Connect across each resistor to take a reading .
First resistance i measure is 100 ohms the reading automatically reads 101.4 so close enough for me
Ill do a few more measurements on resistances and on real resistance components
Below 4.7K resistance
Below 470k or 0.470 M ohms
Now ill do some real resistance components
Next capacitors so i select capacitance on dial and them blue button to shift to capacitance mode
First one i read is 3.3 micro farads
Then a 0.1 micro farad
and lastly a real 0.1 micro Farad capacitor
Next ill test diodes you need to select diode mode on selector dial and this reads the voltage across the diode you need to test both ways one should give a voltage reading the other way should not allow current to flow and hence show OL on meter
OL one way and 0.3v the other so a good diode
Same below but on a real diode component
OL one way and 0.56v the other direction
Now i test transistors you should get voltage one way but not the other similar to a diode as this is what a transistor is a combination of diodes.
You need to test from Base to Collector and Emitter with one lead and then reverse then you should similar to a diode get 2 OL reading and 2 voltage readings
OL reading with red lead to Base and black to Collector
Red to Base black to Emitter
Now reverse leads black to Base and read to Collector and 0.7v
