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#Hard Shut off

Tech Tips:

There is a lot of misunderstanding about the HSO (hard shut-off) or “non-bleed” TXV (thermostat expansion valve) and what makes it shut off, why it exists, and how it “magically” opens. Once you understand the forces inside the valve, it is quite simple, obvious, and sadly devoid of any magic. The Three Forces The TXV […]

Non-bleed TXVs and Hard Starts – Short #257

In this short podcast episode, Bryan talks about non-bleed TXVs and whether they need hard starts. A non-bleed (hard shutoff) TXV is a metering device that shuts off during the off cycle; it closes shut when there is no superheat. This strategy prevents refrigerant migration, especially in cases where we have long line sets. […]

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In this short podcast episode, Bryan talks about non-bleed TXVs and whether they need hard starts.

A non-bleed (hard shutoff) TXV is a metering device that shuts off during the off cycle; it closes shut when there is no superheat. This strategy prevents refrigerant migration, especially in cases where we have long line sets. Liquid refrigerant stays in the condenser and is kept out of the evaporator, suction line, and compressor crankcase.

When we have a non-bleed TXV, the compressor may have a hard time starting under the conditions created by the hard shutoff TXV (high head pressure, low suction pressure). Reciprocating compressors are more likely to have this problem than a scroll or rotary compressor. If you have a short line set, 230+ voltage, and a scroll compressor, you probably won’t need a hard start kit. You may need a hard start kit if you have a reciprocating compressor, a longer line set, or 208V power.

The OEM will recommend a hard start kit that is suitable for the equipment. Aftermarket hard start kits are okay if a compressor is old and struggling, but they’re not the preferred option and should be as close to the OEM’s recommendation as possible. Hard start kits typically consist of a start capacitor and a potential relay. Positive-temperature coefficient resistors (PTCRs) also exist, and these have a resistor that heats up and eventually takes them out of the circuit. Hard start kits should not be added to inverter-driven equipment and are not meant to compensate for voltage drop issues; they can cause more harm than good if they’re used when they’re not necessary or not used correctly.

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Non-bleed TXVs and Hard Starts – Short #257

09/16/2025

Bryan Orr

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