The materials inside determine, to a large extent, how long an air conditioner or chiller will last, how efficiently it will run and what faults it will develop. A copper pipe with the wrong wall thickness, an incompatible oil, an uncoated coil in a coastal area or insulation exposed to UV means early failure, no matter how good the unit is. In this guide we explain the main materials used in air conditioning and refrigeration systems, their properties, where they are used and what to watch for in the field.
Copper pipe
The pipe used in refrigerant lines is high-purity, phosphorus-deoxidized copper (Cu-DHP, EN 12735-1 / ASTM B280 ACR pipe). It is supplied with the inner surface cleaned and the ends capped, so moisture and dirt do not enter the circuit. Plumbing pipe made for water installations must not be used in refrigeration lines.
| Type | Feature | Use |
|---|---|---|
| Coil (annealed, soft) | Bends easily, can be flared | Small diameters (1/4" – 3/4") in split and VRF lines |
| Rod (hard, straight) | High strength, straight and neat runs | VRF main lines, large diameters, chillers and cold rooms |
| Inner grooved | Grooves on the inner surface increase heat transfer | Inside coils, heat exchangers |
| Pre-insulated copper | Insulation applied at the factory | Residential split installations |
Sizes and wall thickness
Refrigeration pipe is referred to by its inch size: 1/4" (6.35 mm), 3/8" (9.52 mm), 1/2" (12.70 mm), 5/8" (15.88 mm), 3/4" (19.05 mm), 7/8" (22.22 mm), 1-1/8" (28.58 mm) and larger. With high-pressure refrigerants such as R410A and R32, the operating pressure is significantly higher than with R22; for this reason the wall thickness must be chosen according to the pressure resistance required by the refrigerant and the diameter. Wall thicknesses of generally 0.8 mm for small diameters and 1.0 mm or more for large diameters are used; for the exact value, the manufacturer's manual and EN 12735-1 apply. An old line laid for R22 must not be reused with an R410A or R32 unit without checking wall thickness and cleanliness.
Common problems with copper
| Problem | Cause | Prevention |
|---|---|---|
| Formicary (ant-nest) corrosion | Contact of copper with organic acids (vapors from some adhesives, cleaning agents, insulation and wood); very fine pinholes form | Install away from the source of contamination, use suitable insulation, avoid suspect chemicals |
| Oxide (scale) on the inner surface | Nitrogen not passed through the pipe during brazing | Pass dry nitrogen at a low flow rate through the pipe during brazing |
| Flare leak | Wrong flare size, burrs, excessive or insufficient torque | Correct flaring tool, deburring, tightening with a torque wrench, flare size suitable for R410A |
| Vibration crack | Compressor vibration transmitted to the pipe | Vibration dampener, correct clamping, pipe support |
| Crushing and kinking | Wrong bending, sharp turns | Bending spring or bender, observing the minimum bend radius |
Brazing materials
Refrigeration lines are joined not with soft solder but with brazing alloys that melt above 450 °C. The right alloy is chosen according to the metals being joined.
| Alloy | Composition | Used with | Note |
|---|---|---|---|
| Phosphorus copper (BCuP) | Copper + phosphorus, 0-15% silver | Copper – copper | No flux needed for copper-to-copper; as the silver content rises, flow and vibration resistance increase |
| Silver alloy (BAg) | High silver, copper, zinc | Copper – brass, copper – steel, copper – stainless | Flux is required; residue must be cleaned off |
| Phosphorus alloy + steel | — | Steel and stainless | Phosphorus alloys form a brittle bond on steel and are not used |
Aluminum, fins and coils
Coils generally use aluminum fins fitted over copper tubes. Aluminum is light, inexpensive and a good heat conductor; however, at the point where it contacts copper it can suffer galvanic corrosion in humid and salty environments.
| Coil / coating | Feature | When it is preferred |
|---|---|---|
| Copper tube – bare aluminum fin | Standard, economical | Normal urban environment |
| Hydrophilic-coated fin | Lets condensate run off the fin as a film | Indoor unit coils, heat pump outdoor units (defrost) |
| Epoxy / "blue fin" / "gold fin" coating | Protects the fin surface against corrosion | Coastal areas, light industrial environments |
| Electrophoresis (e-coat) or polyurethane coating | Protection that coats the entire coil | Seaside, chemical plants, wastewater treatment plants |
| Copper tube – copper fin | No galvanic couple forms; durable | Heavily corrosive environments, marine applications |
| Micro-channel (all aluminum) | Less refrigerant, compact, light | New-generation chillers and outdoor units; repair requires a different method |
As fin spacing (FPI, fins per inch) increases, the coil becomes more compact but more sensitive to fouling. On coils with dense fins, filtration and regular cleaning are even more important. Coils must never be washed with high-pressure water at a right angle, stiff brushes that crush the fins must not be used, and strongly acidic or alkaline cleaners that damage aluminum must be avoided.
Steel, galvanized and stainless steel
| Material | Feature | Where it is used |
|---|---|---|
| Galvanized sheet | Zinc-coated steel; economical, basic protection against corrosion | Unit cabinets, ducts, support profiles |
| Electrostatic powder-coated sheet | Baked-on paint over galvanized or steel | Outdoor unit and chiller cabinets |
| AISI 304 stainless steel | General-purpose stainless | Drain pans, hygienic air handling unit interior surfaces, kitchen hoods |
| AISI 316 stainless steel | Contains molybdenum; more resistant to chlorine and salt | Coastal areas, pool dehumidification, plate heat exchangers |
| Black steel pipe | Welded, high strength | Chiller and boiler water piping (closed loop) |
| Cast iron / ductile iron | Heavy and durable | Pump casings, butterfly valve bodies |
Heat exchanger materials
| Heat exchanger type | Material | Point to watch |
|---|---|---|
| Brazed plate (BPHE) | Stainless steel (usually 316) plates, copper or nickel braze | Water quality and filtration are critical; sensitive to clogging and freeze damage. Copper-brazed types are not used in ammonia circuits |
| Gasketed plate (PHE) | Stainless or titanium plates, EPDM/NBR gaskets | Can be dismantled and cleaned; gasket material is chosen according to the fluid |
| Shell and tube | Steel shell, copper or copper-nickel tubes | Scale and sludge on the water side; regular brushing or chemical cleaning |
| Coaxial (tube in tube) | Copper or copper-nickel | Small water-source heat pumps; freeze protection |
Refrigerants (gases)
For each gas's GWP value, safety class, area of use and alternatives, see the refrigerant gas guide.
The refrigerant is the "blood" of the system, and every refrigerant differs in pressure, efficiency, safety class and global warming potential (GWP). The safety class per ISO 817 / ASHRAE 34 is shown by a letter (A: low toxicity, B: high toxicity) and a number (1: non-flammable, 2L: low flammability, 2: flammable, 3: highly flammable).
| Refrigerant | Type | Safety class | GWP (approx.) | Typical use and notes |
|---|---|---|---|---|
| R22 | HCFC | A1 | 1810 | Older split, VRF and chiller units; harmful to the ozone layer, not used in new equipment |
| R410A | HFC blend (near-azeotropic) | A1 | 2088 | Split and VRF; significantly higher pressure than R22, POE/PVE oil |
| R32 | HFC single component | A2L | 675 | New-generation split and VRF; low flammability, pay attention to installation rules |
| R407C | HFC zeotropic blend | A1 | 1774 | Alternative for older R22 units; has temperature glide, charged in the liquid phase |
| R134a | HFC | A1 | 1430 | Screw and centrifugal chillers, automotive (older) |
| R404A | HFC blend | A1 | 3922 | Commercial and industrial low temperature; being phased down due to high GWP |
| R513A | HFC/HFO blend | A1 | 631 | Alternative to R134a |
| R1234ze(E) | HFO | A2L | < 10 | New-generation chillers; very low GWP |
| R1234yf | HFO | A2L | < 5 | Automotive air conditioning |
| R290 (propane) | Natural (HC) | A3 | 3 | Small-capacity units, commercial cabinets; highly flammable, charge amount limited |
| R744 (CO2) | Natural | A1 | 1 | Supermarket refrigeration, hot water heat pumps; very high pressure |
| R717 (ammonia) | Natural | B2L | 0 | Industrial refrigeration; toxic, not used with copper and copper alloys |
The GWP values are the commonly used IPCC AR4 values. The European Union F-gas Regulation and the fluorinated greenhouse gas legislation in Türkiye are gradually reducing the use of high-GWP refrigerants. For this reason, in new projects the choice of refrigerant directly affects gas and service availability over the life of the unit.
Basic rules when working with refrigerants
- Different refrigerants are never mixed
- Zeotropic blends (R407C, R404A, etc.) are charged in the liquid phase
- Charging is done by scale according to the nameplate value
- Refrigerant is collected with a recovery unit, not released to the atmosphere
- With A2L and A3 refrigerants, ignition source and ventilation rules are observed
- Use a manifold, hoses and vacuum pump suitable for the refrigerant
Compressor oils
Compressor oil does not only lubricate; it also seals, carries heat and circulates through the circuit with the refrigerant. For this reason the oil must be miscible with the refrigerant. The wrong oil prevents the oil from returning to the compressor and leads to bearing damage.
| Oil type | Compatible refrigerants | Feature |
|---|---|---|
| Mineral oil (MO) | R22 and older CFC/HCFC systems | Little affected by moisture; does not mix with HFCs |
| Alkylbenzene (AB) | R22, some transitional blends | Good flow at low temperature |
| Polyol ester (POE) | R410A, R407C, R404A, R134a, R32 and HFOs | Very hygroscopic: quickly absorbs moisture from the air and can form acid with moisture |
| Polyvinyl ether (PVE) | R410A, R32 (some VRF and split manufacturers) | Hygroscopic, but more resistant than hydrolysis-prone POE |
| Polyalkylene glycol (PAG) | R134a and R1234yf automotive air conditioners | Generally not used outside automotive |
POE and PVE oils must not be left in an open container; the oil can that has been used should be closed immediately, and only the type and viscosity of oil specified by the manufacturer should be added to the system. An annual oil analysis (moisture, acid number, metal particles) on screw chiller compressors shows the internal condition of the compressor without dismantling it.
Gasket and O-ring materials
| Material | Compatibility | Note |
|---|---|---|
| CR (neoprene) | R22 and mineral oil | May swell or harden with HFC and POE |
| HNBR | R410A, R134a, R32 and POE/PVE oils | Common O-ring material for new-generation refrigerants |
| NBR (nitrile) | Mineral oils, water | May not be suitable with POE in the long term |
| EPDM | Water, glycol, steam | Not used in oil and refrigerant circuits |
| FKM (Viton) | High temperature, many chemicals | May be incompatible with ammonia and some HFOs |
When a service valve, Schrader valve or filter is replaced, the old O-ring must not be reused; a new O-ring suited to the refrigerant should be fitted, lightly lubricated with system oil.
Insulation materials
On cold lines, the main job of insulation is to prevent condensation as much as to prevent energy loss. For this, thermal conductivity (λ) must be low and water vapor diffusion resistance (μ) must be high; otherwise moisture gets into the insulation, the pipe sweats and corrosion begins.
| Material | Thermal conductivity λ (approx.) | Vapor diffusion resistance μ | Use |
|---|---|---|---|
| Elastomeric rubber (NBR/EPDM-based, closed-cell) | 0.033 – 0.038 W/mK | High (generally ≥ 7,000) | Refrigerant and chilled water lines, duct surfaces |
| Polyethylene (PE) foam | 0.035 – 0.040 W/mK | Medium–high | Residential split lines, economical applications |
| Glass wool / rock wool | 0.032 – 0.040 W/mK | Low (vapor barrier cladding required) | Duct thermal and acoustic insulation, fire resistance |
| Polyurethane / PIR foam | 0.022 – 0.028 W/mK | High | Pre-insulated panel ducts, cold room panels |
| Phenolic foam | 0.020 – 0.025 W/mK | High | Pre-insulated duct panel, high fire performance |
- Insulation outdoors should be protected against UV with cladding or paint
- Insulation joints should be sealed airtight with adhesive and tape
- Thickness should be chosen according to pipe temperature, ambient temperature and humidity
- The fire class (EN 13501-1) must be suitable for the project and the building
- Insulation must not be crushed at clamp points; insulated clamps should be used
- Wet insulation does not dry out; it must be replaced
Air duct materials
| Material | Feature | Use |
|---|---|---|
| Galvanized sheet duct | Durable, non-combustible in fire; insulated on the outside | General ventilation and air conditioning ducts |
| Pre-insulated panel duct (PIR or phenolic, aluminum-faced) | Lightweight, insulation built in, quick installation | Commercial buildings, ceiling void applications |
| Stainless steel duct | Resistant to corrosion and grease, hygienic | Commercial kitchen exhaust, laboratories, food facilities |
| Black sheet (welded) duct | High temperature and fire resistance | Kitchen exhaust and smoke extraction (according to the relevant regulation) |
| Aluminum flexible duct | Flexibility at connections | Grille and diffuser connections; should be used over short distances |
| Textile (fabric) duct | Even air distribution, lightweight, washable | Gyms, production areas, food facilities |
Water piping, glycol and water chemistry
| Material | Feature | Use |
|---|---|---|
| Black steel pipe | Welded or threaded; common in closed loops | Chiller, fan coil and boiler piping |
| Galvanized pipe | Zinc-coated | Open loop and domestic water (not recommended in a glycol loop) |
| Copper pipe | Easy to install, corrosion-resistant | Small-diameter fan coil connections |
| PPR / PEX | Plastic, does not corrode | Low-temperature-difference applications, underfloor heating |
| Brass valves and fittings | Easy to machine, durable | Small-diameter valves and connections |
Glycol (antifreeze)
Glycol is added to the water in chiller, heat pump and process circuits where there is a risk of freezing. Glycol lowers the freezing point but reduces the water's heat-carrying capacity and increases viscosity; for this reason, a higher-than-necessary ratio increases pump energy and capacity loss.
| Ratio (by volume) | Ethylene glycol freezing point (approx.) | Propylene glycol freezing point (approx.) |
|---|---|---|
| %20 | -8 °C | -7 °C |
| %30 | -15 °C | -13 °C |
| %40 | -24 °C | -21 °C |
| %50 | -37 °C | -33 °C |
- Propylene glycol is preferred where there is a risk of contact with food and drinking water
- Inhibited (corrosion-protected) industrial glycol must be used; automotive antifreeze must not be used
- The glycol ratio should be measured with a refractometer every season
- pH, conductivity and inhibitor level in closed-loop water should be monitored
- Water hardness and Legionella risk must be managed in humidifiers and cooling towers
- Zinc can dissolve when galvanized pipe is used with a glycol loop
Electrical materials
| Material | Feature | Note |
|---|---|---|
| NYM cable | PVC-insulated, fixed installation | Indoor supply lines |
| H07RN-F cable | Rubber-sheathed, flexible, suitable for outdoors | Power supply to outdoor units and rooftop equipment |
| Communication cable (shielded, twisted) | Protected against interference | VRF and control lines; routed separately from power cable |
| Contactor | Silver alloy contacts | Compressor and fan motor switching |
| Capacitor | Metallized polypropylene film | Microfarad (µF) and voltage ratings must match exactly |
| Voltage protection relay | Phase loss, phase sequence, under/over-voltage protection | Recommended especially for units with control boards and inverters |
Fan and motor materials
| Part | Material | Note |
|---|---|---|
| Axial fan blade | Cast aluminum or glass-fiber-reinforced polypropylene (PP-GF) | Composite blades are light and corrosion-resistant; they vibrate if balance is lost |
| Radial (centrifugal) fan wheel | Galvanized sheet, aluminum or composite | Backward-curved wheels are more efficient |
| AC motor | Copper-wound induction motor | Runs with a capacitor or a drive |
| EC motor | Permanent magnet, integrated electronic drive | High efficiency at variable speed; must be protected against moisture and overvoltage |
| Bearing | Steel ball, sealed or greasable | Life depends on load, temperature and lubrication |
Materials and corrosion measures by environment
| Environment | Risk | Recommended measure |
|---|---|---|
| Seaside (coastal) | Salty air; rapid corrosion on aluminum fins and steel cabinets | Coated or copper-copper coil, 316 stainless connections, frequent washing |
| Industrial area | Sulfur, nitrogen oxides, chemical vapors | E-coat coil, epoxy-painted cabinet |
| Indoor swimming pool | Chlorine and high humidity | 316 stainless, coated coil, corrosion-resistant fan |
| Commercial kitchen | Grease vapor, high temperature | Stainless duct, grease filter, frequent cleaning |
| Wastewater and treatment plant | Hydrogen sulfide (H2S); attacks copper and silver brazing | Coated coil, positioning the unit away from corrosive air |
| Hospital and laboratory | Disinfectant chemicals, hygiene | Stainless interior surfaces, hygienic-design air handling unit |
Compatibility summary: refrigerant, oil and gasket
| Refrigerant | Oil | O-ring / gasket | Pipe and wall thickness |
|---|---|---|---|
| R22 | Mineral (MO) / alkylbenzene (AB) | CR (neoprene) | Standard refrigeration pipe |
| R410A | POE or PVE | HNBR | Wall thickness suited to high pressure |
| R32 | POE or PVE (depending on manufacturer) | HNBR | Wall thickness suited to high pressure; A2L rules |
| R407C | POE | HNBR | Standard; charged in the liquid phase |
| R134a | POE | HNBR | Standard |
| R1234ze / R513A | POE (depending on manufacturer) | Elastomer approved by the manufacturer | Standard |
| R717 (ammonia) | Mineral or PAO (depending on the system) | Elastomer suited to ammonia | Steel or stainless; copper is not used |
For more technical terms, see our glossary of terms; for replaced parts, our spare parts guide; for filter materials, our HVAC filters page.
Frequently asked questions
Can copper pipe installed for R22 be used with an R410A or R32 unit?
In some cases it can, if the wall thickness suits the pressure of the new refrigerant and the line is thoroughly cleaned. However, old oil residue, flares and wall thickness must always be checked, and the manufacturer's line reuse instructions must be followed.
Why should POE oil not be left open to the air?
POE oil is highly hygroscopic; it quickly absorbs moisture from the air. Wet oil forms acid in the system and damages the compressor windings and bearings.
Which coil should be chosen in coastal areas?
Aluminum-fin coils with epoxy or e-coat coating, or copper-copper coils, should be chosen; the unit should be washed regularly with fresh water.
What is the difference between elastomeric rubber and polyethylene insulation?
Elastomeric rubber has a closed-cell structure and high resistance to vapor diffusion, so it is safer against condensation on cold lines. Polyethylene is more economical, but it is generally less preferred for applications with cold water or where a long service life is expected.
Can automotive antifreeze be used in a chiller circuit?
It is not recommended. The additives in automotive antifreeze can form deposits in HVAC circuits. Inhibited industrial ethylene or propylene glycol should be used.
Is R32 flammable, is it safe?
R32 is an A2L class refrigerant, meaning low flammability. It is used safely when correct installation, appropriate charge amount, ventilation and ignition source rules are followed.