Might want to try a very short segment of capillary tubing setup post HX that'll dump all the R1150 from the HX and rob the evap of refrigerant. I need to re-do mine to put a solenoid on the oil return also but this does work rather nicely on my evap, it warms up very quickly. Not a perfect solution but I didn't want to dump oil laden refrigerant into the evap.