Fridge part of fridge freezer not working. Top part working fine but no cold air coming down to fridge part. Defrosted freezer two weeks ago and worked fine afterwards for about 10 days, then fridge part stopped working again. Applicance 12 about years old. Any suggestions

Freezer achieving -5 is good airflow at the top is good. You have a return air problem something is blocking airflow back to freezer. Look for a vent in the Fresh Food side along the dividing wall could be as simple as product against the vent. Vent could also be behind crisper drawers. If all of that is clear Pull freezer cover and look for ice or frost buildup in vent.

As far as your freezer frosting up, sounds like a door seal problem, run your fingers along the seam of the door seal, there should be no splits/holes in the seal.
As far as the refrigerator either there is a secondary fan motor, or there is a obstruction blocking the air movement, if the freezer has a bad seal, its suspect ice is still building up.

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If freezer is ok and cooling ( 5 degrees or less) one thing you might want to check is that the flow of cold air to refrigerator is not obstructed by the items in your freezer. The ductwork has to be available. Also check the opening of the damper if fridge is not cold enough. And is the fan operating at full speed - are the bearings dirty and slowing it down?
Also check your freezer temp - there are degrees of freezing. Water freezes at 32 degrees but a good freezer should go down to about zero. And the colder your freezer air is the colder your fridge will be.

seal on door must be letting moisture into compartment, need new door seal

It sounds as if the freezer coils and vent stack are frozen solid. This usually requires
removing the back panel in the freezer compartment and defrosting carefully with
a hair dryer. (If this becomes frozen it blocks off the fan/vent that feeds cold air down to
the fresh food compartment) Make sure to unplug unit before servicing as you will need
to unplug the fan to remove the back panel.
While doing this check the defrost termination thermostat (a small device attached to
the tube with two wires coming out of it). The black plastic ones sometimes come apart
and fail.
Once defrosted put everything back together and test.
Hope this helps.

this alarm is activate if the temp. of the fridge rises and because the freezer section is full of ice form thats why affect the circulation of cold air. try to check the defrost timer if yuor unit have or heater if working if dont have defrost timer or heater try to lessen the setting of your themostat to cut of unit after reaching desired temp. or conduct weekly defrost manually.

There is nothing that work in the fridge it is just a box everything comes from the freezer. Check if the fan is running this is how the fridge gets its cold air. Check your freezer setting in your fridge. make sure it says warmer fridge. it a door that opens and closes.

Had a similar problem with my Kenwood Fridge Freezer
If you're mechanically minded you could check if there's an opening and motorised flap (usually behind a cover) at the top of the fridge - Cold air from the freezer enters the fridge through this flap) The Sound you heard could have been the motor trying to open / close this flap. This flap can become frozen in the closed position - so cold air is unable to enter the fridge compartment) My fix was to thaw it with a hairdryer and reassemble. Another fix would be to empty the freezer and open the doors - it might take more than 24 hours but once completely defrosted if the flap is the issue it will have defrosted. Once plugged in again the door will open and cold air will start to flow into the fridge compartment. I had a quote for €195 for a call out / repair
I fixed it myself in an hour - Hope it works for you ...

There is a duct between the freezer and refrigerator. Sometimes this duct blocks off with ice and won't allow airflow. Open your refrigerator door and check for air flow if there is none the duct needs to be defrosted. turn off freezer/ refrigerator and defrost.

The defrost cycle is not happening like it should, that's what causes the block of ice (and poor air flow). If you have all that defrosted look at the defrost bi-metal, it usually is a small round disk with a couple wires coming out of it and it's clipped on the coils. When it's cold enough, it passes electricity to the heat elements, when it gets hot enough it "opens" and kills power to the heat elements. If that is bad (swollen cracked or bloated) and not passing electricity to the elements that's the problem. Another item would be the defrost timer itself, if it doesn't work (no clock motor turning) then it will never go into defrost. And the last and usually least expected failure would be the heat element themselves not working