CSLB C-20 HVAC ContractorCooling and RefrigerationMedium
A technician needs to replace a failed compressor on a system with a liquid line service valve, without releasing refrigerant into the atmosphere. Which procedure allows the technician to isolate the system's refrigerant charge in the outdoor unit before opening the system?
- APerforming a pump-down procedure, closing the liquid line valve and running the compressor to draw refrigerant into the condenser/receiver, then closing the suction valve
- BPerforming a triple evacuation using a vacuum pump
- CPurging the system with dry nitrogen to displace the refrigerant
- DRecovering the entire charge into an external DOT-approved cylinder using a recovery machine
Show answer & explanationAnswer & explanation
Correct answer: A. Performing a pump-down procedure, closing the liquid line valve and running the compressor to draw refrigerant into the condenser/receiver, then closing the suction valve
A pump-down procedure uses the compressor itself to move refrigerant into the condenser and receiver by closing the liquid line service valve first, then shutting off the compressor once suction pressure drops, isolating the charge without a separate recovery machine.
Why the other options are wrong
- B. Triple evacuation is for moisture/air removal after opening a system, not charge isolation.
- C. Nitrogen purging is used for brazing atmosphere control, not charge isolation.
- D. Recovery is valid but not the specific technique described using existing service valves and the compressor.
Pump-Down Procedure
A method of isolating refrigerant charge in the outdoor unit by closing the liquid line valve and running the compressor until suction pressure drops, then closing the suction valve.
- Requires service valves on both liquid and suction lines
- Avoids need for external recovery equipment
- Prevents atmospheric release during minor repairs
Memory trick: Pump it down, lock it in the condenser.