On an R-22 system, line diameters and lengths should typically not exceed what vapor pressure drop?

The correct choice reflects standard practices in the design and operation of refrigerant systems, particularly with R-22. Maintaining an appropriate vapor pressure drop is crucial for ensuring efficient performance and preventing issues such as reduced system capacity or compressor damage.

For an R-22 system, a vapor pressure drop of 6-7 PSI is generally accepted as the upper limit. When the pressure drop exceeds this range, it can lead to insufficient refrigerant flow to the evaporator, resulting in lower efficiency and inadequate cooling. This pressure drop threshold is calculated based on factors such as the size of the refrigerant lines, the length of the runs, and the specific characteristics of the system.

Keeping the vapor pressure drop within this acceptable range helps to ensure that the refrigerant can adequately absorb heat from the indoor environment, resulting in optimal cooling performance. Hence, the significance of this 6-7 PSI threshold lies in balancing system efficiency with operational reliability, which is vital for troubleshooting and diagnosing issues in HVAC systems.