Answer:
It's not plugged in. A fuse is blown. Oxygen is no longer present because we killed all our trees. The pressure gauge is broken and all your Oxygen is gas because the gauge says you are at 30 atmospheres when you are actually at 1.5. The cooler is outdated and requires CFCs, which are now illegal. The cooler is too small to reduce the temperature of the quantity of oxygen you wish to liquefy. Your liquid oxygen machine is actually a liquid helium machine. The company that sold you your liquid oxygen machine was scamming you and now it looks really complex but in fact if you break it open with a sledgehammer, you will see that the inside is made completely of useless nonbouyant rubber duckies. Operator error.
Explanation:
All are entirely possible and would cause a liquid oxygen machine to be defected.
