My two rheem compressors sit side by side outside. Both SEEM to work normally in heat mode. HOWEVER, the smaller 1.5 unit gets no frost buildup at all and the lines stay lukewarm both outside and at the airhandler in my attic. Aux heat comes on for both units when temps dip below 35 dgrees as I would expect. Is it possible for the one compressor to be doing its job without ever getting the lines hot? A tech checked system pressures and freon recently and found all normal...