heating or cooling?
cooling 15-20 deg.
heating, whatever the data plate states for a heat rise, shoot for the middle of that range.
if a heat pump as opposed to fossil fuel, then, as a "rule of thumb" which doesn't mean much, in the heat mode without any aux heat running, at 32 deg o.a., the split should be around 20 deg. for every 3 deg. higher, add 1 deg of split temps.
i.e. 35*=21 split.
29*=19 split.
this is not a perfect example, but only a reference.
good luck