I have a frost free fridge/ freezer, make-Hygena, model-6823.
If i open fridge door and tap thermostat control outer cover compressor will cut in and run till required temperature is obtained then cut out, will not restart till cover is given another tap.
I have removed electrical board/theromostat/bulb to see if anything was slack, nothing was.

Ken Wilson, December 2006

This is a followup to my previous answer. It turns out that changing the relay only fixed the problem for a few months. The underyling problem was that the voltage on the low voltage side was getting lower and lower (should have been 24V, got down to 12V) due to a faulty capacitor. (Changing the relay helped temporarily because the new relay needed less power to energise it.)

I later replaced C1, C2 and C3 which cured this voltage regulation problem. However be very careful if you do this. C1 is a high-voltage type and the whole circuit is a not a very brilliant way of generating 24V from the mains (no isolation; possibly wouldn't be allowed today).

Also the fridge went wrong in a different way a few months after this, and I gave up on it and got a new one!

Alex, June 2008

I forgot to say, my email address can be found in the image at http://www.archduke.org/email.gif.

Alex, July 2007

I had the same problem with a Hygena 6825 (which I think is similar). The problem is with the relay on the control PCB which is getting stuck. You could get a new control PCB, though these tend to be expensive (I've seen prices from £80 to £190). I think the part number is 45X8924, but you should check this. If you don't mind a small amount of soldering (and some time spent dismantling the PCB which is a bit tricky) you can actually replace just the relay (which costs about 99p). My original relay was a Schrack or Tyco T7NS5H1-24. I replaced it with a T7NS5D4-24 (RS component number 334-0020). Please let me know if you need more details.

Thanks for your 'tapping' tip. It was extremely useful in diagnosing the problem and saving a fridge/freezer full of produce.

Alex, July 2007

thermostat needs replacing

airkool@hotmail.co.uk, December 2006