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Hunting / surging suction pressure and superheat swings

What is going on

Possible causes and checks for: hunting / surging suction pressure and superheat swings.

Likely causes

  • Oversized valve, superheat set off MSS point, bulb location/contact poor, liquid-charged bulb on wide-range application

Check in this order

  1. Find MSS (A9), re-adjust ≤1/4 turn and wait 10–15 min, check valve sizing, consider cross-charged valve

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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.