TXV system is hunting - superheat swings from 3 to 20 degrees every couple minutes.

Hunting causes & fixes:

1. Sensing bulb mounting (most common issue): - Must be mounted 30° above horizontal on the suction line, 12-18" from the evaporator outlet - Use proper insulation over the bulb and 12" of line upstream/downstream - Bulb must be snug against the line with no air gap - use a thermal paste or aluminum tape - No insulation between bulb and line

1. Check these areas: - Refrigerant charge - verify with superheat/subcooling (not just pressures) - TXV powerhead - ensure proper torque on the bulb (typically 15-20 inch-lbs) - Evaporator airflow - check for dirty coils, duct issues, or blower problems - Liquid line - ensure adequate subcooling (8-12°F typical) and no restrictions

1. System issues: - Oversized TXV for the application - Internal valve problems - check for debris or worn components - Pressure drops in the liquid line

Quick test: If you bypass the TXV temporarily and superheat stabilizes, the valve is likely faulty.

Code reference: Follow ACC A10-2015 for proper refrigerant system installation practices.

If the bulb is properly mounted and charged correctly but still hunting, the TXV itself may need replacement.

Hunting Causes & Checks (in order):

1. Sensing Bulb Mounting (Most Common): Location: On a horizontal suction line run, as close to the evaporator outlet as possible (before any traps). Clock Position: 10 o’clock or 2 o’clock (side mount). Never top (12 o’clock) — stratification gives false temp. Never bottom (6 o’clock) — oil insulation. Contact: Clean copper bright. Tight metal-to-metal contact (strap/clamp). Insulate bulb completely with cork/foam tape and vapor-seal (mastic/tape) — ambient air kills response. Size: Bulb on same diameter pipe as valve capacity rating. Reducer? Mount on larger pipe.

1. External Equalizer: Must be connected downstream of bulb (between bulb and compressor). If missing or plugged → hunting.

1. Valve Sizing: Oversized TXV = hunting. Check nameplate vs. load. 1.5–2x oversizing is max.

1. Superheat Setting: Factory ~10°F. Adjust slowly (1/4 turn = ~1–2°F). Wait 15 min between turns. Don’t chase swings.

1. System Issues: Low charge (flash gas at inlet) → erratic feed. Dirty evap coil / low airflow → unstable load. Non-condensables. Restricted liquid line filter-drier (temp drop across it).

Code/Std: IMC 307.2 (access), 1101.1 (mfr instructions). AHRI 750 (rating conditions).

Do: Verify bulb mount first. Fix insulation/seal. Confirm equalizer. Then adjust SH. Don’t: Mount bulb on vertical riser, trap, or insulated line. Overtighten strap (crushes bulb).