Underbar fridge overshooting set point?

[Drew]

I recentley changed an old underbar fridge from being controlled by an LP switch to a digital carel control. The fridge is a 3 glass door underbar with a large static coil (no fan) mounted on the ceiling. The system cycles directley off the stat with no pump down soleniod valve. The coil has a drip tray underneath it .
Normally I would set the set point at 2 degrees C with a 3 degree differential.
This i did and found that the compressor turned off at 2, but still the cabinet came further down to -1 degree C . I have seen cabinets over shoot the mark by maybe a degree, but this is 3 degrees and would freeze product? Could it be overcharged and all the refrigerant in the overfull reciever is still flowing excesivelly through? Or is due to the static coil holding more refigerant that still is evaporating ( more so than a fan assited coil)??
I have had to set the set point at 5 degrees (with a 1/2 degree diff) to stop the product freezing. Now the cabinet compressor turns off at 5 degees , but the temp still drops to 1 degree and turns back on at 5 1/2 degree. Is this common on a static coil?

[raz5]

you may want to consider placing the st1 probe closer to the static evap . or even attaching it to it the evap coil . you will get residual flash over from refrigerant but you should get a tighter control. Hysteresis of 3 should be fine .

[it was working]

I aggree with raz5 the cabinet would have been fine it was fan assisted the probe position needs to be changed.
no air movement over the probe

[Drew]

Thanks guys. I have placed the probe near the middle shelf thinking it would give a nice average cabinet temp, but i think ill move it closer to the coil.

I have never had this problem with a fan assisted coil.
Is it because the coil holds more refrigerant thats still boiling off or due to the fact that there is no air movement.?