Filter driers remove contaminants and moisture from the refrigerant in HVAC systems. They contain a desiccant for moisture absorption and a filter medium to trap particles, ensuring clean refrigerant flow. Filter driers are typically located in the liquid line of the system, between the condenser and the expansion valve. They are essential for the longevity and efficiency of HVAC systems, helping to ensure clean and dry refrigerant circulates through the system.
How Does a Filter Drier Work?
Filter driers remove particles and contaminants from the refrigerant, such as dirt, metal shavings, and debris that could potentially harm the system by clogging the expansion device or damaging the compressor. Desiccant material, such as silica gel or molecular sieves, absorbs moisture from the refrigerant. This is crucial because moisture in the system can freeze and obstruct the flow of refrigerant or react with the refrigerant and cause acid formation, which can damage system components.
Core Components of a Filter Drier
Outer Shell
The outer shell of a filter drier is usually made from steel and houses the internal components. It is designed to withstand the pressure of the refrigerant flowing through the system.
Desiccant Material
Desiccant material is the moisture-absorbing component inside the filter drier. Common materials used include silica gel, activated alumina, or molecular sieves. Each type has different properties regarding moisture absorption capacity and the ability to handle various refrigerant types.
Filter Medium
Alongside the desiccant, a mesh or felt-like material is used to trap physical contaminants. This prevents particles from moving through the system, where they could cause wear or clogs.
Check out this video from The Engineering Mindset for more information on what's inside a filter drier:
Filter Drier Placement
In most HVAC systems, the filter drier is strategically placed in the liquid line between the condenser and the expansion valve. This location allows the filter drier to clean the refrigerant after it has condensed and before it enters the expansion valve, ensuring that only purified and moisture-free refrigerant circulates through the system.
Watch as the experts at The Engineering Mindset explain how filter driers work in HVAC systems:
Types of Filter Driers
Liquid Line Filter Driers
Positioned on the liquid line of the system, these filter driers are the most common type used in both residential and commercial HVAC units. They protect the expansion valve and remove contaminants and moisture from the refrigerant after it exits the condenser and before it enters the evaporator.
Suction Line Filter Driers
This type of filter drier is used on the suction side of the system to protect the compressor from contaminants that might return with the refrigerant from the evaporator. Suction line driers are particularly important in systems that have experienced compressor failure or when there's a risk of acid buildup.
Bi-Directional Filter Driers
Designed for use in systems such as heat pumps, where the refrigerant flow can reverse direction depending on the heating or cooling mode, bi-directional filter driers have a design that effectively filters contaminants and moisture regardless of the direction of refrigerant flow.
Burnout Filter Driers
These are specialized filter driers used to clean up the system after a compressor burnout. They contain more activated charcoal or other adsorbents to remove acids and other byproducts generated during the burnout, helping to restore the system's cleanliness and efficiency.
Core Shell Filter Driers
These filter driers have replaceable cores, allowing easy maintenance and replacement without replacing the entire shell, which is advantageous in larger commercial systems that require frequent maintenance.
Filter Drier Applications
To maintain system integrity and efficiency, filter driers are crucial in various HVAC applications. In residential and commercial air conditioning systems, they prevent moisture and contaminants from damaging compressors and expansion valves. They are also essential in heat pumps, which operate both heating and cooling cycles, requiring clean and dry refrigerant to function effectively. In specialized environments like server rooms and medical facilities, filter driers help maintain precise temperature and humidity levels, which are critical for operational reliability.
In this video, the experts at Sporlan discuss ways to remove system contaminants from the low and high sides of vapor compression refrigeration systems.
Maintenance & Replacement
Filter driers are not permanent components. Their capacity to absorb moisture is finite. Once saturated, they can no longer protect the system effectively. Regular monitoring and replacement are necessary, especially after system maintenance or any incident that might introduce moisture into the system. Replacing a filter drier involves:
- Recovering the refrigerant
- Removing the old one
- Installing a new one
- Ensuring the flow direction is correct
- Recharging the system with refrigerant
Filter Drier FAQs
How often should a filter drier be replaced?
Replacement should occur whenever the system is opened for repairs that might contaminate the refrigerant or if the system shows signs of moisture, such as ice formation or reduced cooling efficiency.
This video from Sporlan addresses instances when a filter drier should be replaced:
Can a filter drier be cleaned and reused?
No, filter driers are designed to be replaced, not reused. Once the desiccant is saturated, it cannot be regenerated effectively in the field.
How do I know if a filter drier is failing?
Symptoms include a decrease in cooling efficiency, frost on the compressor, or visible signs of rust or corrosion near the drier itself.
Does the size of the filter drier matter?
Absolutely. The size of the filter drier should be compatible with your HVAC system's size and refrigerant charge. Incorrect sizing can lead to inadequate moisture removal or restricted flow of refrigerant.
Filter Driers by Manufacturer
Alco Controls Filter Driers
Alco Controls filter driers with exchangeable cores for liquid and suction lines are used in refrigeration systems to absorb moisture and acid and filter out impurities. They also have a full line of hermetic and non-hermetic filter driers for all applications.
Features of Alco Controls Filter Driers
- ODF copper fittings for easy brazing (FDH plated steel)
- For liquid and suction applications with replaceable cores
- Optimum flow capacity at low pressure drop
- Corrosion-resistant epoxy paint
- Medium temperature TS: -45…+65°C
- Max. allowable pressure PS (according medium temperature): -10°C...+65°C: 34.5 bar ADKS-Plus, FDS 46 bar, FDH -45°C...-10°C: 25.9 bar
- Compatable with R134a, R404A, R407C, R450A, R452A, R448A, R449A, R507, R513A, R410A, R744 (sub), R1234ze
- Uniflow
Shop Alco Controls Filter Driers
Carrier Filter Driers
Carrier filter driers are engineered for efficiency and equipped with high moisture and acid removal capacities to ensure the refrigerant remains clean and dry. Available in both suction and liquid line configurations, they are suited for a wide range of applications, from residential air conditioning systems to large commercial setups.
Danfoss Filter Driers
Danfoss's range of filter driers covers both hermetic and exchangeable core types. The core helps the filter drier absorb water and acids more effectively, preventing corrosion of the compressor's metal surfaces and ensuring that oil and refrigerant do not decompose.
Features & Benefits of Danfoss Filter Driers
- A solid core with a fast adsorption rate, a superior flow capacity, and a low-pressure drop minimizes maintenance and running costs.
- Dedicated models for liquid and suction lines, bi-flow, and receiver combined with filter driers
- Suitable for A/C, commercial refrigeration, transport and CO2 applications
- Long-lasting and reliable protection
- Solder, flare, flare o-ring, and face seal connection types
- Pure copper, Cu-platted, and steel connection materials
Danfoss Hermetic Filter Driers
Danfoss Semi-Hermetic Filter Driers
Read more about Danfoss filter driers in this case study from Danfoss – Filter driers: just the facts.
Sporlan Filter Driers
Sporlan's Catch-All series sealed model filter driers provide excellent contamination control to ensure the full life, capacity, and efficiency of air-conditioning or refrigeration systems up to 20 tons.
Features & Benefits of Sporlan Filter Driers
- Complete contaminant control to protect and extend system life and ensure system reliability
- High-performance desiccant package provides high water capacity and acid capacity
- Porous molded core provides excellent filtration of solid debris for TEV and compressor protection
- Sizes from 3 cu. in. to 60 cu. in. and 1/4" to 1-1/8" fittings for use up to 20 tons cooling capacity
- Models available with activated charcoal for use during system clean-up
- CSG models have an integrated liquid and moisture-indicating sight glass to allow visual refrigerant examination
- SAE flare fittings and solid copper ODF fittings are available
- Suitable for use with HCFC, HFC, HFO, and HC refrigerants
- UL Listed for 650 psig rated pressure for R-410A and Sub-critical CO2 refrigerant use
- RoHS, REACH, ATEX, and PED compliant
Other Manufacturers
Liberty Suppy carries filter driers for many other HVAC brands, such as Lennox, Amana-Goodman, Bard HVAC, ClimateMaster, Friedrich, and many more.