In the Field: Commissioning a New Mini-Split Heat Pump

ReVision Energy tech Dave Ragsdale explains how to make sure a new Mitsubishi mini-split heat pump is fit for service.

Commissioning a Mini-Split

ReVision Energy technician Dave Ragsdale on site with a newly installed Mitsubishi mini-split system on an older home in rural Maine. Hanging from the compressor unit is a set of pressure gauges and valves.

Pulling the Core

Ragsdale removes the "core" from the service port of the mini-split's refrigerant line fitting. He will pressure-test and vacuum-flush the lines through this port.

Fitting an Adapter

Ragsdale attaches an adapter to the service port that will allow him to pressurize and evacuate the line set directly. He will attach his "micron gauge" to a side port on the adapter, permitting highly accurate pressure readings during the evacuation test.

Adapter Valve

The pressure-testing adapter fitting has its own valve for opening and closing the system during the tests.

Adapter Side Port

This fitting on the testing adapter allows the installer to attach a sensitive pressure gauge without using hoses that might affect the measurements.

Attaching the Pressure Gauges

For the high-pressure leak test, Ragsdale hooks up a gauge that reads in pounds per square inch (PSI). He will pressurize the line set to about 150 PSI more than its usual operating pressure and leave it under pressure overnight.

Pressurizing the Lines

Ragsdale releases pure nitrogen (N2) into the line set, watching the gauge to monitor the pressure.

Under Pressure

The pressure gauge reads about 600 PSI (pounds per square inch), well above the mini-split's maximum operating pressure of 450 PSI.

Evacuation Testing

The day after the pressure test, Ragsdale returns to conduct a triple-evacuation line-set purge in cold, rainy conditions.

Pumping Out

In place of the PSI gauge he used for the high-pressure test, Ragsdale has connected a "micron gauge" to the test adapter, along with the vacuum pump (sitting on the ground).

Vacuum Pump

A closer look at the vacuum pump, used to suck nitrogen out of the line set at near zero pressure. Moisture boils into the low-pressure gas and is also pumped out of the line set to eliminate the risk of corrosion.

Pressure Drop

With the vacuum pump running, nitrogen pressure in the line set starts out at about 11,000 microns, but quickly drops.

Deep Vacuum

It's not quite the vacuum of deep space, but 170 microns is a very low pressure. Ragsdale will observe the gauge for a few minutes to make sure the system isn't leaking, then refill with nitrogen, repeating the evacuation process a total of three times.

Filling the Line Set

After the triple-evacuation process is complete, Ragsdale opens a valve on the compressor unit and releases its stored refrigerant into the cleaned and evacuated line set.

Removing the Adapter

With the successful purge completed and the refrigerant charge installed, Ragsdale removes the testing adapter from the unit's service port. The "incidental" release of a small amount of refrigerant is allowed by EPA rules.

Capping Off

Ragsdale replaces the cap on the unit's service port. Tested, cleaned, and charged with refrigerant, the fully commissioned mini-split is now in service and ready to begin heating the home.

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