vacuum pump is not running but unit still run

The primary thing that will happen is that the temperature will rise very rapidly and yes, you will get some significant noise coming from the centrifuge. Having frost in the chamber is really not a big deal unless it gets very thick. The vacuum is only operating at 1/4 vacuum so that is why frosting still happens depending on environmental conditions around the centrifuge. Lots of humidity in the room will tend to generate lots of frost in the chamber.

There is a relay that controls the operation of the vacuum pump and it is activated by the timer. Both the timer and the vacuum pump have been known to fail. Replacing or possibly rebuilding the vacuum pump if it is frozen is a possibility as it is a Gast manufactured carbon vane pump. There is no oil in the pump and if you get liquids down into the pump it will have very serious consequences for the pump.

Getting a replacement timer assembly is very problematic. The original manufacturer went out of business and Beckman could not find a suitable substitute or get anyone to make one. As long as the timer can be placed in HOLD mode then the vacuum pump should turn on and then you just use a lab timer to tell you when to shut down the run.

Really need more information as to exactly what is going on like rotor being spun, how fast, does the timer still work, if you drop the front cover do you hear the vacuum pump even try to start. Get back to me and we'll go from there but please take note, the J2-21 series centrifuge was obsolesced over 10 years ago and getting service or service parts may be an issue, especially from Beckman Coullter.

Don

thank you Don for replying. i got 220v on/off as the timer control. it just the vacuum pump is frozen i just order one.  Have a happy Holidays,