Install a TXV (Thermostatic Expansion Valve)

Mount close to the coil, clamp the sensing bulb on a clean horizontal suction line at 4–5 o'clock and insulate it, tie the external equalizer downstream of the coil, braze with N2 + heat-sink, then set/verify superheat.

Approx. 90 min

Before you start

•System recovered/isolated so the lines can be opened safely — never braze on a charged system.
•Correct TXV: matched to refrigerant, capacity/tonnage, and the right bulb charge; internally- vs externally-equalized chosen (most coils with meaningful pressure drop need EXTERNAL equalization).
•A clean horizontal section of suction line available near the evaporator outlet for the sensing bulb.

Tools & materials

Brazing torch + rod + flux as needed · Tube cutter + deburring tool · Nitrogen + regulator (brazing purge), wet rag/heat-sink compound · Bulb clamp/strap + closed-cell insulation tape · Manifold + pipe-clamp temp probe (for superheat), vacuum pump + micron gauge

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Mount the valve

Mount the TXV close to the evaporator inlet
Locate the valve as close as practical to the evaporator's distributor/inlet so it can meter accurately and respond quickly. Support the lines so the valve body isn't carrying pipe weight.
Target: Valve at/near the coil inlet; distributor/feeder tubes correct for the coil

Sensing bulb

Clamp the bulb on a clean horizontal suction line at 4–5 o'clock
Mount the sensing bulb on a clean, straight HORIZONTAL run of suction line right at the evaporator outlet, clocked to the 4 or 5 o'clock position (NOT the bottom, where oil pools and gives a false-cold reading; not the top). Clamp it tight with full metal-to-metal contact so it senses true suction-line temperature.
Tools: Bulb clamp/strap
Target: Bulb at 4–5 o'clock on a clean horizontal suction line, full contact, strapped tight
⚠ Clean the pipe to bare copper under the bulb — paint, dirt, or scale insulates the bulb and skews superheat.
Insulate the bulb from ambient
Wrap the bulb (and the surrounding pipe) with closed-cell insulation so it senses the refrigerant temperature, not the ambient air around the coil. An uninsulated bulb reads warm and the valve overfeeds.
Target: Bulb fully insulated from ambient with closed-cell wrap

External equalizer

Connect the external equalizer downstream of the coil
Tie the external equalizer line into the suction line just DOWNSTREAM of the evaporator outlet (after the bulb), so the valve sees true evaporator-outlet pressure and compensates for the coil's pressure drop. Wrong-side or omitted equalization on a coil with real pressure drop causes severe underfeeding/high superheat.
Target: Equalizer tapped into the suction line downstream of the coil, just past the bulb

Braze it in

Braze with a nitrogen purge and heat-sink the valve body
Flow dry nitrogen through the line while brazing the inlet/outlet to avoid internal oxide scale, and protect the TXV body and its diaphragm/power head with a wet rag or heat-sink compound. Overheating the valve damages the internal charge and the diaphragm.
Tools: Nitrogen + regulator, Brazing torch, Wet rag/heat-sink compound
Target: Low N2 purge during brazing; keep the valve body/power head cool with a wet rag/heat-sink paste
⚠ Never trap nitrogen between two closed points while heating. Remove the power head if the maker requires it for brazing. Fire watch.

Evacuate & set superheat

Pull a vacuum, then restore the charge
Pressure/leak-test, evacuate the opened section to a deep vacuum with a decay test, then restore/verify the charge before commissioning the valve.
Tools: Vacuum pump, Micron gauge
Target: Evacuate ≤ 500 microns and hold before charging
Set and verify superheat to the target
Let the system stabilize, then read superheat at the bulb location (suction line temp minus saturation temp for the suction pressure). Adjust the valve in small increments (give it minutes to settle between turns) to the target superheat. On a TXV system the charge itself is verified by subcooling.
Tools: Manifold + pipe-clamp temp probe
Target: Evaporator superheat to target (commonly ~8–12°F; verify per design); allow settling time between adjustments