Pump down
Pump down turns up in 2 fields: HVAC, vacuum. Here is what it means to the people in each one.
Pump down in HVAC
Moving a system's refrigerant into the condenser or receiver by shutting the liquid line and running the compressor.
Closing the liquid line service valve or solenoid while the compressor runs empties the low side, and the compressor stops on low pressure, leaving the charge stored on the high side. Techs do a manual pump-down to work on the low side without recovering the charge. Commercial refrigeration often uses automatic pump-down every cycle, so liquid cannot migrate to the compressor during the off cycle.
"Do a pump down to 5 psi on the low side, front-seat the suction valve, and we can change the TXV without recovering."
Pump down in vacuum
To evacuate a chamber from atmosphere to its working pressure, through roughing, crossover and high vacuum.
To take a chamber from atmosphere to operating pressure; as a noun, a pump-down is the whole sequence of roughing to crossover, opening the high vacuum valve and pumping to base or process pressure. In the rough range the time follows t = (V/S)·ln(p0/p), set by volume and pump speed, while in high vacuum outgassing takes over, so a clean, dry chamber pumps down in minutes and a wet one takes hours.
"Pumped down at seven and we're at 5E-6 already, the door seal must have been the problem."