Lytron Recirculating Chiller Model# RC 030 J01 M05

I recently replaced a compressor in a Lytron recirculating chiller. After running
the unit right after the compressor replacement everything seemed fine. Dishcarge
line from compressor was hot to the touch while the suction line was cold to the
touch. The water tank of the recirculating chiller started to drop in temprature.

However, after four hours of operation the unit became unable to to maintain temp.
Furthermore, the expansion valve(metering device) got iced up. I tend to think
that I didn't put enough refrigerant (R134a). It used R134A before the compressor
replacement. I put the exact same copeland compressor back in and recharged with
R134A.

I have actually never replaced a chiller compressor before so I wasn't sure how
much refrigerant goes in the unit. If I remember correctly I left the low side
around 20psi which still gave me about 300psi on the high side. I actually wanted
the low side around 60psi but I figured that'll probably make the high side explode.

It did bother me that such a low pressure on the low side is yielding such a
high pressure on the high side but the unit seemed to be working ok so I left it.
Now I want to add more refrigerant but am afraid to raise the high side pressure
too much.

Can anyone guess as to why the high side is so high? which is what scares me from
adding more refrigerant. I am universally certified but still new to commercial
refrigeration.

Thanks