My freezer not staying cold

The defrost thermostat is good. It closed when i tested it after putting it in the freezer and opened when it warmed up again to room temp,. The thermostat sits on the evap coils and measures the coolant temp coorect. If its low on freon would this affect the defrost? if the defrost timer is bad is the defrost heater on more than 20 minutes or does it prevent the compressor from starting?

@ehrmy1

Low on Freon would mean that it doesn't cool properly i.e not get to the set temps, so either the freezer compartment would be too warm or perhaps both compartments and the compressor would be hot to the touch or at least hotter than usual

I don't think that the defrost thermostat measures the coolant temp per se. it is just that you don't want the evap unit to get too hot and be damaged from the heater which is directly below it as it is only thin Aluminium and the coolant is extremely cold. As the defrost cycle occurs approx. every 10 hours there is not that much ice build up if everything is working OK so it doesn't have to take long to melt it all

If you look at the wiring diagram in the parts link I posted then the defrost thermostat will prevent the heater from operating after the thermostat has operated but the defrost timer contacts may stop the compressor from restarting. You may have to catch the fridge in defrost mode and then check if it restarts OK at the end of the cycle.

If the compressor and evap fan are both stopped for >15 minutes then it is probably in defrost mode (except perhaps in the middle of the night when there is not much user activity i.e. doors not opened a lot, so that the cold air is lost and has to be replaced, so no need for the compressor to run) but the fridge should restart again if more than 35 minutes have passed since you first noticed it was stopped especially if you gently open a door.

I say gently because if the timer is the problem the vibration from opening the door maycause the timer contacts to make again and start the compressor. The evap fan won't start because a door is open. It only works when the compressor is running and the doors are shut.

If it is still stopped when you open the door (>35 minutes) tap the timer and check if this causes the compressor to start

Unfortunately I don't know how to 'force" a defrost cycle in your model so that you can more easily check

I will try changing the defrost timer first because obviously something is keeping the compressor from starting. The fridge is in my shop so it is hard monitoring the defrost cycles. initially after being unplugged for a while changing parts etc it runs normally but it seems odd that i can get it(compressor) to start by turning up the control temp to max from normal at the start but the same thing happens again when the temp is at max. that is the compressor wont start again because i cant turn the temp up anymore

@ehrmy1

The compressor operating circuit goes through both the defrost timer and the temperature control thermostat so it could be either one that is preventing it from starting.

What happens if instead of turning the control temp thermostat from normal to max if you turn it from normal to min and then back through normal to max again, does the compressor start? If so it may be the control thermostat. Apologies if you've tried this already

During the normal course of operating when the refirgerator reaches the set temp the compressor and the evap fan should turn off and then restart again maybe a few minutes later when the temperature has risen above the set threshold in the compartments and it needs to be driven back down again to remain within the parameters of the control thermostat's lower and upper temperature limits.

Basically the compressor should cycle on and off (with it being on longer than being off due to doors opening etc) to maintain the temperatures within the operating limits and should only be off for a prolonged time (in comparison to the other "off" times) during the defrost cycle or perhaps overnight when there is less activity and therefore less need to operate the compressor to maintain the temp as the temp is more stable.

If it does this OK then I'm thinking it is more a defrost timer problem as it only has to restart the compressor once every 10 hours after a much longer compressor off time.

Did you try tapping the defrost timer (part #23 - shelves parts diagram) when the compressor has been off for a prolonged time i.e. 30 minutes, you never said?

In the end you may have to get technical and use a Voltmeter to see if there is voltage at the compressor when it should be operating and it isn't. If there is no voltage being applied to the compressor then you have to start tracing it back to find out why not.

There is a wiring diagram in the parts list I linked although admittedly it is hard to read as it is faint but it's better than not having one