Kaeser AS30 will not load

Jim Karg asked 1 year ago

I have a Kaeser AS30 built in the 90’s.  The compressor will turn on and pressure in the sump will only reach 25lbs.  It will not go into load stage because of the inadequate pressure in the sump.  What is causing it to not build enough pressure to go into load stage?  Bad solenoid valve? The vent valve diaphram is not torn but the o-ring on the piston looks suspicious. 

3 Answers
Cas Staff answered 1 year ago

Hi Jim,

Not wanting to ‘load’ can be many things, but I agree that 25 psi (1.7 bar) is a bit low for unload pressure.

Did you check the minimum pressure valve? As the name implies, it maintains a minimum pressure. It is situated at the outlet of the compressor, usually (99% of the time) on top of the separator vessel.

If it is leaking, air will leak into your compressed air system and the pressure inside the compressor will become low during unload running.

Please also check the loading solenoid. Just disconnect it (the outlet) and load/unload the machine. Make sure control air blows out when the compressor is ‘loaded’. Most inlet valves on stationary compressors are ‘normally closed’ so without control air, the inlet valve is closed.

Last thing, even when the inlet valve is closed, there should be a small hole or bypass, so a little air is taken in by the compressor. This little air is what generates the internal unload pressure needed for the control air. The same amount of air is blown of again, so the unload pressure stays stable.

If that hole is dirty or plugged, the unload pressure will drop as well.

Hope this was useful. Please let me know if you find the problem. And if you need more info, don’t hesitate to ask.



Jim answered 1 year ago


Thank you very much for the response.  One  thing we have discovered while troubleshooting is that when we warm up the room that the compressor is in, it will begin to load.  It seems that once the temp gauge on the compressor reaches 165 degrees it will begin to load.  It is still cold here in Pennsylvania with overnight temps in the 20s-30s and if I turn the compressor on first thing in the morning, it will run indefinitely without loading.  But if I add a source of heat (been using a torpedo heater) to warm up the room, the compressor will load once the gauge hits 165*F.  I thought it could be a coincidence but it has worked at least a dozen times like this, and it seems that about 165* is the magic number.  Is there some sort of minimum temperature switch on this machine that could be faulty?  I’m really stumped on this one.

Chuck answered 1 year ago

Try closing the sump vent valve on top of the separator lid. If it loads like that, your inlet valve/actuator is worn and needs rebuilt. The seals are rubber and don’t seal under sump pressure when cold. Don’t forget to open the vent valve back up or you’ll be lifting the relief valve.