Understanding the Use of Suction Filters/Driers
They can help protect compressors when used right
It is important to have refrigerant that is free from debris and contaminants, and we control these issues on many different fronts:
- Proper tubing handling preventing copper shavings, dirt, and water from entering while installing
- Flowing nitrogen while brazing to prevent carbon buildup
- Deep vacuum of 500 microns or less to remove air, nitrogen, and moisture
- Installation of a liquid line filter drier to keep contaminants from hitting the metering device
But in all of this we can easily forget the role that suction driers can play in protecting the compressor and the compressor oil.
In air conditioning, we rarely install suction driers unless there is known acid contamination, such as in the case of a compressor burnout. Interestingly, Copeland actually recommends suction driers in all applications in bulletin AE24-1105 R5. While I certainly don’t think that we need to change our practices and begin installing suction line filter driers on every single installation, it does get you thinking about the role a suction drier can play in protecting a compressor.
In a typical burnout application where acid is present, it is a good practice to:
- Remove/flush as much contaminated oil from the system as possible considering the application, including any oil traps, separators, or accumulators.
- Install a high capacity acid removal suction and liquid drier or removable core(s)
- Some contractors will add acid neutralizers in certain applications
- Return after running the system for a while and test for acid and replace high capacity filter/driers with new ones if required.
- Once acid is no longer present, return and remove the suction filter/drier and install a standard liquid line drier or core.
These practices above are good general practices to follow, but you may consider replacing the suction drier with a standard, high capacity, low-pressure drop suction drier with two pressure ports instead of just straight piping it. This will provide you an extra layer of protection for the compressor should any acid or contaminants from the burnout make their way to the compressor.
If you do choose to leave a suction drier in a system, there are a few things to consider:
- Just like with a liquid line filter drier, make sure to install a suction filter/drier that is large enough for the system capacity. Read the info on the drier or the manufacturer’s data to make sure it is large enough, so you don’t start off with a restriction.
- Make sure you don’t burn the paint on the drier when installing. Because suction driers on air conditioning will often be exposed to the elements, you want to make sure the paint is intact so they don’t rust.
- Use a suction filter/drier with ports on both sides and measure the pressure drop whenever you service the unit. Make sure the pressure drop does not exceed proper levels.
All in all, having a suction drier in the system is a good thing, so long as it isn’t contaminated, rusty, or restricted.
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