I can get A/C to come on normal but when I switch t-stat to heat it blows the transformer in about 3 or 4 minutes. This is a Goodman 3 ton air handler with a 10 k.w heat strip. This is a straight air unit and not a heat pump. I have checked all the wiring against wiring schematic and all wiring is correct. I also noticed the transformer is humming when you first put t-stat in heat position and then 3 to 4 minutes latter the transformer blows. The blower motor and the heat strips never come on before the transformer blows.