If for any reason the pump will not operate:
1- Turn off the power and check the fuse and electrical connections. Compare the pump motor rating, printed on a label on the side of the motor and on the serial number tag, to the power source, to be sure they agree in voltage, phase, and frequency.
2- The pump will not start against very cold viscous oil, (below 12C degrees). If oil in pump is cold and viscous, change oil with clean, warm oil.
3- The exhaust port is blocked or restricted due to a clogged pipe, filter (if fitted).
4- The pump has seized due to long storage
The most common cause of of vacuum pump failure is contamination of oil.Oil contamination is caused by condensable vapor condensing in the pump as the mechanisms compress the vapor. The condensate emulsifies with the oil and is recirculated through the vacuum pump, forming a sludge or polymerized oil will adhere moving parts together when the pump is at rest, impairing the pump's ability to start.
Periodic oil changes are necessary to avoid the vacuum pump seizing due to poor quality of oil or contamination of the pump oil.