DIY Mini split installation- What Type Pre-charged Line Set Best?


Many people start with the DIY Mini split air conditioner or heat pumps due to COVID-19 and expensive installation costs. The pre-charged line sets do not need a professional technician to help install. you can do it yourself.

What are Pre charged Line Sets?

Copper line sets with Refrigerant R410 or R32 already exist pipe inside before installation which means it is pre-charged from the factory and 100% ready to go right out of the box.

Precharged line sets the structure

  •  4 female quick couplers attach to four pipe ends
  •  4 male quick couplers attach to outdoor unit service valve
  • Dual Pipe length from 15ft to 50ft customized

precharged line set

Quick coupler pipe connecting Type 

According to the copper pipe with quick coupler connecting method, we can find two types, one is flame welding pipe connecting with quick coupler, another is flared nuts screws on quick coupler

  • Flame welding body with quick connector 

precharged line set

Quick connector welding to small parts copper pipe that also flames welding to copper pipe body. Every pipe ends have 4 place welding points.

  • Pipe Flare nuts screw on the quick connector 

precharged lines

Female quick couplers have universal thread connecting to flare nuts, it is compatible with all model flare nuts 1/4″ 3/8″ 1/2″ 5/8″3/4″ 7/8″.

Flame welding body  VS flare screw on body 



What is the same about two types connecting?

  • It is precharged refrigerant already pipe inside from the factory
  • pre-charged line sets can make DIY Mini-split heat pump come true

What is the difference between two types connecting?


Flame welding features:

Flame welding produces the amount of oxide material inside which possibly comes into AC units capillary tube cased blocking when operation, flux residues, and hot scale on the surface.

  • Too fast crystallization of copper, water vapor is too late to escape, reaction pores are formed inside
  • Oxide material produced by flame welding falls off and comes into ac units easily, block the capillary tube.
  • Water vapor insoluble in copper, oxygen-containing copper is easier formed reaction pore than oxygen-free copper

Flame welding destroy the copper original structure, make mechanical properties like tensile strength, Elongation, and bursting pressure became weaker than before

Original Copper pipe mechanical properties:

Alloy grade: C12200
Tensile strength: 215~275MPA Elongation:δ10 (%):≥25
Max working pressure:2.1~4.15 MPA

After flame welding copper pipe mechanical properties:

Tensile strength: 150~180 MPA
Elongation: :δ10 (%): 20~30
Max working pressure: 1.8~2.8 MPA


Flare screw-on pipe features

quick coupler

The female quick coupler end has a thread that compatible with flare nut internal thread.

  • NO any flame welding on pipes that avoid slow leakage in a long time.
  • “plug and play” applicable for any brand AC units, applicable fluid temp:-30°C to +120 °C.
  • 4th generation line sets can help change from Non-DIY line set to the Real DIY line set
  • Multiple reuse quick connectors, when repair a broken line sets, just replace pipe body and release refrigerant into lines, the same installation with conventional line set.
  • For flame welding on pipes, when the pipe broke happen just disposable quick connector

Flare screw-on connect Test.


  • Airtightness

Fill in 4.3MPA nitrogen, 3min in water, no air bubble happen, and drying.

  • Sealing

Fill in freon R410, stay in 48 hours, and do leak detection.

  • High-Temperature capability

1.5 times locking toque tighten, put in 120°C±3°C surroundings. After 48 hours, flare nut should not be visual crackle and defect.

  •  Low-temperature capability

1.5 times locking toque tighten, put in -30±3°C surroundings. After 48 hours, flare nut should not be visual crackle and defect.

  • Vibration Resistance

2 times toque fixed on the vibration device as vibration frequency 48Hz and 3mm amplitude. Vibration time: up and down 8 hours, No cracking and loosening happen.

  • Stress corrosion resistance

Use 14% ammonia solution, 10L evaporating dish sealing container, and The test temperature is 20 ~ 30 °C, The corrosion time of the sample is 72 hours.

4th generation precharged line sets we use flare screw on connect method to avoid disadvantage of 3th generation precharged line sets with flame welding on pipe body.

Some audience ask me the question, “How to repair pre-charged line sets” ? if we found copper pipe body broken or deform happen.

Multiple reuse quick connectors can solve this issue and make a new precharged line set again. I will share with you in my next articles and do specific explain.