Samsung RS21 fridge is not defrosting and its building ice and will not dispense water

Samsung RS21 fridge defrost problems

youtube videos:

test the RS21 thermal fuse:

test the RS21 defrost sensor:

test the RS21 tray heater:

test the RS21 evap heater:


There are several reasons why the RS21 units cause fridge defrosting problems. This guide is intended to help you unravel what is wrong and what you need to fix the fridge problem. It is only going to deal with specific components within the fridge cabinet, it will not cover refrigeration gas systems at all.

This applies to RS21 SRS2026 SRS2028 and SRS2029 fridge sections

A common indicator is that the temp readings on the door display do not alter, yet the unit has turned off. Several components can indicate the same error symptoms therefore it is important to checkout all the relevant components at the same time. Another common failure is a whirring noise from the unit, which stops as the fridge door is opened. Yet another is the unit works for 12 hours (approx) then defrosts.

Within the RS21 fridge section, behind the water bottle and the back panel is an evaporator, this is the system part that is absorbing heat from the unit and food products. Whilst the cabinet is frost free the evaporator isn't, it gradually builds a covering of frost/ice as heat and moisture is removed from the air within the fridge section. If left to build ice, it eventually restricts the air flow, blocks the drain hole of the cabinet, penetrates the insulation of the back panel, blocks the fan drain hole which stops the fan running or creates noise as the ice surrounds the fan blade, freezes the cool water bottle, sometimes splitting it and prevents the fridge section from working correctly. 

There are reasons for this happening, one of which could be the gas system is not 100% correct. In our experience this is the least likely cause of fridge failure, but also the one where specialist knowledge, training and equipment would be needed. So best left alone other than to say if the following guide to the components proves them to ALL be ok, it should then become a consideration. As should a defective PCB control component.

The defrost components

To keep the ice build up in check the unit goes into defrost mode, you will be unaware of this happening, the programme is built into the electronic control and cycles almost silently until it goes wrong. There are 2 defrost heaters, 1 defrost sensor and a protecting thermostat (TOC) involved in defrosting the evaporator. One heater fixed into the vanes of the evaporator keeps the evaporator clear of excessive ice build up, as that ice melts the tray heater ensures the water runs out of the cabinet via the drain hole. Please note, that if this water were to re freeze and remain in the cabinet the next defrost cycle will add more water and then ice to the problem. It is very important that both heaters are fully functional. To control the heaters the defrost sensor monitors the rise in temperature during the defrost cycle, the electronics responds to the rising temperature to switch the heaters off. There is a protection device which is a "one shot" safety fuse. It is strapped to the refrigeration tube of the evaporator and will respond to any overheating by the elements during the defrost cycle, once tripped it disables the heaters until service investigation discovers it.

Failure of one or more of these can lead to the insulation of the back panel becoming saturated with water/ice and in turn causing fan problems. The back panels already have a drain hole for water to exit the cabinet and prevent build up of ice around the fan, defrosting the fan has been a problem area for these units for some time. There is a modified back panel that transfers heat from the evaporator defrost heater to the drain hole area during defrost cycling. 

Testing the components

Before any testing is carried out the unit should be

1) Switched off and the plug removed from the wall socket. Under no circumstances is "live" testing required to ascertain the electrical standing of the following components.

2) Defrost the fridge fully before you start


Removing the shelves and water bottle gives access to the screws holding the back panel in place. There is a sealing strip around the back panel, if you try to remove without defrosting you can damage this seal. Damaging the seal will effect the air flow and cause over icing on the evaporator. Hand held steam guns are ideal for quick defrosting, but care should be taken to avoid damage to plastics and components within the fridge. We have seen damage to cabinet liners where huge wallpaper steamers have been used to quickly defrost the ice away, this will cause insulation failure of the cabinet, don't use them.

Once you have the back panel removed the following readings can be obtained using a multimeter.

Defrost sensor
......this has been modified and if yours is a white coloured bullet sensor head you should replace it with the latest one, which is black. The white ones are known to ingress moisture with the contraction and expansion of the plastic head unit, causing defrost problems. If you have a black bullet sensor head then it should read at 20*C, 6.01Kohms, at 21*C, 5.79Kohms. At -20*C it reads 32.4Kohms. The sensor reacts to heat very quickly. If you don't get these readings at these temperatures the sensor should be considered faulty.

Evaporator Defrost element...
this has to be isolated from the tray heater plug, testing it connected to the tray heater will result in an incorrect reading. Once isolated it should read 485ohms, we have recorded these at 200 ohms and to earth, so its 485ohms or very close to it for the heater to pass the test.

Tray Heater ....
this is self adhesive and stuck in place, isolated from the other heater it should read 2.1Kohms. if it does it's ok, check for shorts to earth as well.

thermal fuse (TOC) ......
strapped to the refrigerant tube of the evaporator this should have electrical continuity, usually less than 0.1 ohms, don't forget to measure the resistance of your leads and deduct that reading from the final reading.

If any of the above components is faulty you need to replace them. If the insulation of the back panel is shot because of ingress of moisture you need to replace it. If you just defrost and replace a faulty panel you'll be doing it every 3 to 4 weeks, it all only works if all components are good. 

There is a modified back panel, which allows heat from the evap heater to warm the drain hole of the fan motor during the defrost cycle. This mod comes with instructions on how to fit the evaporator clip into place. There are different back panels depending on which RS21 you have, the  RS21J and RS21K coolzone models and the  RS21 without coolzone. These 2 links are back panels only, if you want a kit of 5 parts, read on.

We make up a kit of all the defrost components which is available in the shop

it includes a back panel and 4 defrost components, just click the link to view, it is for the RS21 without coolzone.

Finally, before you rebuild the fridge section, just check using a small cup of water that the drain hole and channel through the cabinet are clear. About 4 inches down the drain channel takes an approx 90* bend, we have found this bend blocked with ice, the hand held steamer soon clears it. Left blocked the ice problem soon returns.

** Just a note regarding reliabilty of these parts, if fitted correctly our experience shows that the replacement parts are very reliable and over the last 2 years only a handful of heaters have failed within 18 months of replacement. Only 1 sensor has failed to our knowledge and we have used hundreds. ***