Resideo (Honeywell) TMX-00039 Thermostatic Power Element – R404A, MOP −10 °C | For TMX Series TXV

Resideo (Honeywell) TMX-00039 is the upper body of the TMX series thermostatic expansion valves with interchangeable orifice (thermostatic power element). While the valve body stays brazed in the line, the charge type is determined by this upper body; in the event of a fault or a change of application, only the upper body is replaced without removing the valve body.

R404A Gas Charge, MOP −10 °C Compressor Protection

MOP (Maximum Operating Pressure) is a pressure limiter that prevents the suction pressure from rising above a certain value: at start-up, after defrost and during warm pull-down, the valve throttles and compressor overload is prevented. In this model the MOP value is −10 °C; according to the official Resideo table it operates in the −10 °C to −50 °C evaporating range — the band of deep freezers and low-temperature commercial refrigeration.

Technical Specifications (Official Resideo Product Data)

• Model: Resideo (Honeywell) TMX-00039
• Type: TMX series interchangeable upper body (power element)
• Refrigerant: R404A (same charge band as R507A)
• Charge: Gas charge, pressure limiting — MOP −10 °C
• Evaporating Range: −10 °C … −50 °C
• Max. Pressure: PS 34 bar(a) · test pressure PF 37.4 bar(a)
• Capillary Tube: 2 m | Sensing Bulb: Ø16 mm | max. bulb temperature 140 °C (gas charge)
• Static Superheat: ≈ 3.5 K (adjustable)
• Dimensions: Ø52 · height 53 mm · ~0.60 kg — official dimensional drawing in the 2nd image
• Equalizer Connection: 7/16" UNF (integrated in the externally equalized valve body)
• Material: Stainless steel thermostatic head + stainless diaphragm welded under shielding gas, brass body
• Compatibility: TMXB (flare) / TMXL (solder) bodies + TMXD orifice cartridges

• 🚨 With gas-charged MOP elements, the sensing bulb must always be COLDER than the capillary tube and the thermostatic head — otherwise the charge migrates to the head and the valve loses control. In the TMX series this condition is met naturally, because the thermostatic head is warmed by the liquid refrigerant.
• MOP value selection: It should be selected according to the maximum permissible suction pressure of the compressor, or at least 5 K above the operating evaporating temperature of the system.
• 🔧 When replacing the upper body check that the orifice cartridge suits the capacity — the orifice determines the capacity, the upper body the charge.