GE HumiLab Operator's Manual page 11

clean, oil-free gas, regulated at 1 to 2 psig at 5 lpm (minimum).
Connect the dry air or dry nitrogen source using the 1/4"
"instant-on" DRY AIR IN connector on the rear of the unit. See
Figure 2, Humilab Rear View.
Figure 2 — Humilab rear view (gas, A/C, and signal connections)
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Chapter 1 — Installation and Initial Setup Page