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Pump won't pull a deep vacuum

What is going on

Possible causes and checks for: pump won't pull a deep vacuum.

Likely causes

  • Dirty/wet pump oil (white, foamy)
  • Leaking hose fittings
  • Permeable/collapsed standard hoses
  • Schrader cores or piercing valves restricting
  • Hoses too long/small

Check in this order

  1. Change oil, test pump alone to 500 µ via tee, use metal/heavy-duty short ½" hoses, remove cores, use real ports

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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.