Jim Bergmann returns to the HVAC School podcast to cover some advanced topics in evacuation, including rig setups and triple evacuation.

To increase the speed of evacuation, you need two large-diameter vacuum hoses to overcome the limitations of pressure. Core removal is also critical, as Schrader cores are a significant restriction. It's also unwise to use a manifold for evacuation; a manifold will double your hose length, provide a restriction, and serve as a leak point.

The vacuum pump is full of opportunities to expand your advanced evacuation knowledge. The pump oil needs to stay clean, and Jim recommends changing the oil after every use. When it comes to pulling the vacuum, it's worth noting that the vacuum is deeper at the pump than at the system itself. The vacuum at the pump does NOT reflect the vacuum at the system; core tools can isolate the vacuum pump from the system so that you can measure the true vacuum at the system.

When we "break" with nitrogen, we're referring to nitrogen sweeps at different stages of evacuation (especially in the case of a triple evacuation). Triple evacuations are rarely necessary nowadays, but you may need to break with nitrogen from time to time. Nitrogen moves through the system so quickly that breaking with nitrogen often has a minimal impact on the vacuum.

The length of evacuation doesn't really affect dehydration until you get below about 300 microns. Dehydration has more to do with the strength of the vacuum than its length.

Jim and Bryan also discuss:

• Locking refrigerant caps
• Assembly lubricants
• Outgassing odors and gas permeability
• Hygroscopic vs. hydrophobic vacuum pump oil
• Vacuum pump oil management
• Average air conditioning decay rate
• Thermistor vacuum gauges
• Nitrogen regulators
• Metering devices
• Gas ballast on vacuum pumps

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