I have a new 38YDB036 and an FE fan coil. It was installed in cold weather so the proper charge is still somewhat in question. He charged it as best he could to going by the heating chart supplied with the unit.
I notice that the frost always forms in bands but does eventually cover all but the bottom of the coil before it goes into defrost which I have moved back and forth between the default of 90 min and 60 mins.
Today the ambient air temp was 55 deg and it was still forming frost in bands. I notice that it also still forms frost when the OAT is 0-5 deg.
My last HP would never frost once the OAT was below about 15-20 deg but did still produce nice warm supply air. It also would not frost once the OAT was above 45 or so.
Would this tell you experts that the charge might be low?