Sab 128 Problems

[marthe1994]

The sab128 has a manual Vi if I remember correctly (don't take my word for it) so I would leave that alone unless the compressor has been recently refurbished.

is it controlled by a Unisab controller?

if so it might show 100% capacity when it's not really in full mechanical slide capacity.

The unisab controller while it is good, may figure out that the compressor is in 100% capacity, based on the suction pressure, discharge pressure and amps and will show 100% in the display, but the slide might only be at 30% load...

The unloading solenoid is normally open, meaning it should be energized as long as the compressor is running and click off when it gets a decrease pulse.
the increase solenoid is normally closed, so that one should be energized only when the compressor is getting an increase signal.

Watch in the unisab display if there is an up or down arrow blinking next to the capacity % in the unisab display, if it's showing 100% and there is an arrow pointing up blinking next to it, it means that the Unisab controller is asking for more capacity, every time the up arrow blinks, the increase solenoid will be activated.

if the display shows 100% in the bottom right and there is no up or down arrow blinking, the unisab is saying that the compressor is now at it's max efficiency.

I'm guessing that the compressor is also fitted with a standard Sabroe capacity indicator like this:
lot-2-sabroe-3448-004-capacity-indicator-johnson-controls-new-h3-2107-c9a4c03054bae46eff89c8bd52.jpg
and if you think it is calibrated... you may be wrong

First of, the text has to be level, then you have to do like MBC said, on either side of the increase and decrease solenoids, there are reg valves, close the reg valve on the decrease side and then disconnect the solenoid on the increase side and use a permanent magnet/service solenoid on the increase side to find the true 100% position. this should be done on an already cooled down plant
Then adjust the 100% (max point) using the screw on the front of the capacity indicator.

Because even when you run in manual on the unisab is working in the background and may reduce capacity while you are pushing increase

The capasity is calibrated. The compressor goes on 100% and everything seems ok. Then suddenly the amps go down from 170 to 140 and suctiongas temperature also rises, apparatently for no reason. It seems to loose capasity and compression. But both the Unisab and the clock show 100 % capasity. It sometimes work, sometimes not.
Is it possible that the capasity is not calibrated when both the Unisab and the clock shows the same? The clock follows the slide mecanicaly, doesnt it?