[RichardL]

The 19C is still a helluva' chiller...
Without a doubt tho', the most complicated and demanding compressor to rebuild.....Ever..
I would strongly suggest pulling the foat chamber cover an cleaning out the screens that stops the large debris from passing thru...
The hot gas line in question acts as a stabilizer on the float action.
Lastly, there is a fairly large check valve located on the float-box end that serves to eliminate compressor reversal during a hi-load situation. It is located on top of the evaporator and can normally be found by looking for a bulge in the insulation about 1 ft. square.
Normally should it fail partially open the motor would overheat at some point, but a loose plate on the valve can cause you exact problem by dropping the head pressure enough to have the evaporator to starve...
I installed quite a few transparent Lexan float covers when all other ideas were tried & failed...So cool to watch them double floats working....
Adjusting the minimum close adjustment higher on both floats by use of the adjusting bolts can greatly reduce the Low-Load-Rumble on the R-114 chillers are known for..

 

[RichardL]

Also see from Carrier literature showing location of economiser dampers, one in the cooler and one in the compressor leading to 2nd stage.Is this the check vavle?

No..That is "Not" the check valve I was Referring too.
The one I was talking about is accessed by a square steel cover plate about 6" X 12" on the very top of the evaporator, about a foot towards the center from the Economizer chamber & float box.
It is a free swinging stainless steel plate hanging verticaly inside a housing...One side of the plate is Evaporator whilst' the other is Condenser pressure.
Its sole purpose is to eliminate compressor backspin should chiller shut down under a good load. The hydraulic vane set-up like you have is not the fastet in vane closing.
Seldom does this "Flapper" give problems, but when it does it will drive a mechanic up the wall in finding the problem source...
As far a the float balls, I have found only one was to leak check them....Solder a shraeder valve fitting on the ball & pump that puppy up to 30-40 PSIG. Visual inspection will only make one look bad...You are looking for teeny-weeny crack and it can be anywhere on the ball..
I have a dollar I will bet against a do-nut hole that one,I would guess upper, ball is cracked....
If I forget to pay...Craig (Absorbertech) will cover the bet..(hehehe)
Leave the shraeders on the balls for the next guy.