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Vacuum rises then levels off above 500 microns

What is going on

Possible causes and checks for: vacuum rises then levels off above 500 microns.

Likely causes

  • Moisture in system (plateau at water vapor pressure for that temp)
  • Plateau ~5000 microns = ice/liquid water

Check in this order

  1. Warm system evenly (lamps/room heat), continue pumping
  2. Find frost/sweat spot

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Source: General HVAC service practice — verify per model. Written in our own words; check the manual for your exact model.

For licensed technicians. Gas, electrical and refrigerant work must be done by a qualified, licensed person. Shut off power and gas before servicing, never bypass a safety control, and follow the manufacturer’s manual for the exact model; it and local codes always take priority. HVACopedia is not affiliated with any manufacturer; brand and model names only identify the equipment.