I had the forward unit give me fits with tripping the main breaker and it turned out (eventually) to be bad corrosion on the lower connection on the heater coil.
Once I clipped and sealed the heater wires the air conditioner worked fine with no further issue.
So, we've been fine without a heater and the.ac is not tripping anything now.
I'm definitely looking to replace the units next year so I'll gladly follow along with what you decide.
SM 209, Adagio