R-Pro › Field cases › Refrigerators & showcases
Manifold Zero & Accuracy Calibration — Reliability Check
Likely causes
Analog gauge zero offset — common after impact or drop
Check: Disconnect gauge from all hoses, expose to atmosphere. Needle should rest at 0 (low side) or 0 gauge = 1 atm absolute (high side). Off-position = zero offset.
What to do: 1) Locate zero adjustment screw (small slot next to 6 o'clock position on dial), rotate with precision driver to align at 0. 2) After adjustment, lightly tap gauge to stabilize needle. 3) Non-adjustable gauges lack precision → replace. 4) Schedule quarterly zero check in maintenance calendar.
Accuracy verification — compare to precision pressure standard or known refrigerant equilibrium pressure
Check: 1) Connect both gauges to a precision pressure gauge (±0.5%) and compare at 1 MPa, 2 MPa, 3 MPa with cylinder operation. 2) Or connect gauge to stabilized 25°C R-134a cylinder → should read 0.667 MPa(g). 3) If error >±5%, discard or send for calibration.
What to do: 1) Within ±2% = pass; ±2–5% = calibration recommended; over ±5% = discard/replace. 2) Digital gauges can be calibrated via USB or Bluetooth — refer to maker manual. 3) Affix calibration certificate to gauge case, store digital copies. 4) Check calibration expiry before each job.
If gauge accuracy is in doubt, defer the job. Wrong diagnosis can disassemble a healthy system or miss a leak. Always maintain 1–2 trusted gauges in known-accurate state — basic foundation of technician credibility.
All 565 cases work offline in R-Pro, with error codes for 62 brands and P-T data for 108 refrigerants.
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