"For the defrost i can shut the unit of wait a few minutes switch the valve and then turn it back on? would this be a safe approach?"
No! The problem is not with timing. In reverse flow there is no restriction in the loop as the check valve paralel to the capillary tube, opens. You let to run so much liquid to the BPHX (in this mode evaporator) on the high pressure it can't evaporate all the juice. Liquid reach the compressor and as liquid is not compressible it destroys the the internals.
But the solution is simple. You can take the other capillary from the indoor unit and install it on the bottom pipe of your BPHX. Watch for orientation!
T.
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