Admiral GC2224GEKB not defrosting

I have originally changed the compressor but did not fit the original make(danfoss compressor fitted as replacement). Since fitting the compressor the fridge freezer has refused to do an automatic defrost. I have changed the control board and done a forced defrost as per the instruction leaflet attached to the fridge freezer. Under the forced defrost the heater comes on fine. I am now wondering if fitting a danfoss compressor has caused the defrost problem as I understand that the defrost is worked out by accumulated compressor run time. Does anybody know if this could be the problem or has anybody fitted a compressor of a different make to this model without further problems. Thanks in advance I hope! Cheers Kez