Clarification of Amana freezer circuitry

[BC1]

Our Amana fridge freezer suffered a sudden thaw and I have been troubleshooting to attempt repair myself. Model is SRD 526 SW and I would describe it as an ‘electrical’ rather than ‘electronic’ freezer. i.e. Built in the pre-circuit board era.
I have read your excellent articles on trouble shooting and freezer auto defrost systems, in particular, and they have been of considerable help in understanding the circuitry.
A schematic is attached showing the arrangement of the freezing and defrosting
components in this machine. It appears that the evaporator fan is energised in series with the defrost heating element when in freeze mode. This is counter intuitive – could someone please explain. Why apply any heat to the evaporator when attempting to freeze? When the defrost timer moves to defrost mode the evaporator fan is short circuited and the heating element gets full 240 volts.
Further, I fail to understand why there are two bimetallic thermostats in series with the heating element. Surely one would have been sufficient.
The cause of failure of our freezer appears to be one of these thermostats going permanently open circuit – I tested it buried in the ice in another freezer. The other thermostat works ok.
In addition to clarification of the circuit I would be oblige if anyone could advise of a source of Amana spare parts. Would a generic bimetallic thermostat be suitable ?

[electrofix]

Re: Clarification of Amana freezer circuitry

no its not

since they are in series the current through the circuit is controlled by the component drawing the smallest current. in this case it is the fan. I dont know the wattage of the fan but suppose its something like 10 to 15 watts. this would mean the max output the defrost heater could dissipate is 15 watts but since its resistance is a lot lower it probably under 7 watts

Dave

[BC1]

Re: Clarification of Amana freezer circuitry

The failed thermostat is marked
37TV31 31066 120178-20
L48-33F J9705

The 48 -33 F will correspond to opening closing temperatures in Fahrenheit.

These will be manufacturer’s part numbers. How can I determine the Amana part number and any suggestions about where it can be obtained. Amana parts seem particularly difficult to source.

[SAMURI]

Re: Clarification of Amana freezer circuitry

Try the UK Whitegoods shop on this site.

E-Mail. spares@ukwhitegoods.co.uk

Bob

[BC1]

Re: Clarification of Amana freezer circuitry

Sourced new thermodisk and tested both of the disks in hot and cold conditions. Checked other component parts where possible. Heater resistance is 122 ohms. Defrost timer makes and breaks continuity as expected.

Switched machine on and waited anxiously as frost started to build on evaporator. After both thermodisks had flicked closed the evaporator fan started running and the temperature in both the freezer and fridge dropped. Operation of the compressor and the evaporator fan were then cycled OFF and ON under the control of the cabinet temperature setting thermostat.
I had set thermostat to mid position for both freezer and fridge and temps of -25C and 3C were held.
The defrost timer only advances when the cabinet thermostat demand is ON so it was several hours later that the contacts advanced to the defrost position. This immediately tripped the RCD in the consumer unit. The trip of the RCD has repeated each time since.
Provided the freezer is at a low temperature the heater is powered whether the freezer is in freeze mode or defrost mode so it does not look like it is a breakdown of the insulation of the heater that is causing the RCD trip. The evaporator is short circuited by the defrost times when it enters defrost mode. Mains is removed from the compressor/ condenser fan when it enters defrost mode.
So near and yet so far !
Suggestions please for the trip.

[admin]

Re: Clarification of Amana freezer circuitry

Hi

I would still be checking the defrost heater. disconnect the heater when it has tripped after turning off then switch it back on.If it doesn’t trip then it’s most likely be the heater..

Bryan

[SAMURI]

Re: Clarification of Amana freezer circuitry

I agree with Brian it will be the defrost heater.

Bob

[Author]

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