i agree valve down the water first!
make sure reversing valve is shifting properly!
also slow down the blower during heat cycles, which will bring up head/suction pressure while heating
if that dont work, recover freon, replace metering devices, check water loop for scale!
and there wont be much left for the refrigeration circuit!
oh ya, dont let the customer intimidate you, remember it has never worked correctly!
the buck stops with you if you play your cards right, then when you get it working the way its supposed to
thats when you name your price!