Sorry it has been crazy here.
I have not solved my problem, infact it has gotten worse. The only way to get the system to stay on line is to pump it down and let it run again.

RANGER1

Hello Clay,
What type of evaporator do you have on bottom of surge drum? Is it a shell and tube or something else as cant tell from pictures.
It is a shell and tube with oil return lines draining the bottom of the evap, surge drum, and sight glass piping back to the oil reciever via a venturi.
I was thinking on two lines,one is product you are cooling have a good flow rate (bye the way what is it )? Flow rate is good, 50gpm.
or or is it freezing up on tubes causing poor heat transfer.Also on fridge side is evaporator logged with oil or a valve say in wet return line not opening properly. Return lines are working, they have sight glasses in them and you can see the flow.
I had ajob recently where a air cooler with a surge drum on ammonia would not pump down at all from a high level because air cooler was oil logged .The surge drum was iced up on level control column etc,
but due to no circulation of refrigerant no cooling or heat transfer took place so level would not lower in vessel.This unit had a leaking liquid line solonoid as well but isolating valve was ok.
Your hot gas low load valve could also have been leaking not helping matters.
Other questions
if the level is ok is commressor loading up and how fast? Level is ok and compressor is loading like normal. it doesnt matter which stage it is in.
has this system been operating ok in the past and is this a new problem ? been an ongoing problem but it is usually solved for a few months by changing or cleaning the HAPhillips float valve cartrige
has any recent work been carried out which could have some link to your problems no work done on it.
has compressor had any oil carry over or oil return issues? no oil problems, oil in the reciever and in the sump.
has product temps been gradually deteriorating? no problem with process temp except when the system goes down
.
US Iceman

Check the hot gas bypass valve to make sure it is controlling properly. If the valve was selected properly the hot gas valve should start to open when the compressor is at the minimum step of capacity control. At that point, the hot gas valve should modulate to control suction pressure.
after pumping down the system last thursday i left the hot gas valve off by accident but the system still shut down on high surge tank level a few times over the weekend.
The surging liquid could be caused by the hot gas valve opening and closing (blowing hot gas into the liquid) or the compressor is loading and unloading causing the liquid to boil violently.

What i dont understand is that the surge tank was STILL surging while i was pumping down. the level was going up and down in the sight glasses like normal (as if liquid was being fed in via float vavle(but it was valved off)).
What could cause the surging???
it was like a violent storm in the tank.

What effect could AIR or NON CONDENSABLES have on the system?
The system is in a vacume when down to setpoint and very well could have leaks.

Thanks
Sorry for the delay.
Clay