I have a LENNOX heatpump with a newer replacement RHEEM outside unit, due to a gas leak at the coils of the original LENNOX unit. It works fine in AC mode, but when it switches to heat, the compressor gets VERY hot over time, and the accumulator starts frosting up from the bottom up. It's a dual fuel, and I switched it over to gas, and the icing leared up almost instantly. In heatpump "heat" mode, the air at the registers is only about 75deg. I'll have to switch it back to heatpump mode to see ig that's happening all the time, or just when the compressor is heating up.
I'm thinking the defrost board might be wacky, but not sure .. .. anyone got opinions ??