Superheat Cannot Be Measured — Gauge or Thermometer Reliability Failure

Question

Accepted Answer

Manifold gauge zero offset or residual pressure. Check: Disconnect gauge and expose to atmosphere — needle should rest at 0. If not, zero is off. After connecting hose, if pressure reads negative (vacuum) or abnormal, residual in hose or faulty gauge. What to do: 1) Adjust zero set screw to position needle at 0 (cheap gauges may not be adjustable → replace). 2) Before connecting hose, press both ends to vent residual pressure. 3) Recommend digital manifold — auto-zero, displays pressure + saturation temp + superheat simultaneously. 4) Calibrate against precision gauge at least quarterly. Inaccurate thermometer — poor surface contact or inadequate insulation. Check: 1) Test in boiling water (100°C / 212°F) or ice water (0°C / 32°F) — verify ±1°C accuracy. 2) After clamping to suction line, if thermometer body wobbles when touched, contact is poor. 3) If exposed to ambient, reading approaches average of ambient and suction temp → false superheat. What to do: 1) Use ±0.5°C accuracy K-type thermocouple or PT100 RTD. 2) Apply thermal grease between suction line and thermometer + use firm clamp. 3) Wrap measurement area thickly with insulation — block ambient. 4) Discard inaccurate surface thermometers, calibrate annually.

Superheat Cannot Be Measured — Gauge or Thermometer Reliability Failure

Likely causes

Manifold gauge zero offset or residual pressure

Inaccurate thermometer — poor surface contact or inadequate insulation

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