Filter Dryer and Receiver. The “screening” actions...

We need the function of filter dryer, to remove any physical material from compressor’s wear and tear, and remove any moisture presence within an air conditioning system.

Filter dryer can either be a separate part to the receiver, or these three parts could be integrated into a single unit.

I have explained the overview of the process, here.


Why filtering, drying, and accumulating refrigerant in a receiver?

We,

  • have air conditioning systems with expansion devices. Be it thermostatic type, or capillary tube. These parts have small and restricted for refrigerant. Hence, we don’t want any system blockage by refrigerant borne particles

  • do not want water to freeze up when temperature within the system falls below freezing point of water. Blockage of refrigerant flow, and compressor damage will happen as a result

Hence we need the filter dryer action.

Receiver is used to accumulate compressed and condensed liquid refrigerant, before entry to expansion device.

This part is essential as the inlet port of the expansion device, has to be filled with liquid refrigerant, for its correct response to load fluctuations.

So, the expansion device will “see” fully saturated liquid at the inlet port.


Filtering principle:

Filtering process is achieved by mechanical action of partitioning the flow. Particles will be trapped, whilst the refrigerant flow will be maintained.


Drying principle:

Drying means we have to remove moisture, and the part that makes it happen, is the desiccant.

These desiccants can be of two types. The,

  • absorbent type, where the moisture will be absorbed into the desiccant. The capacity is determined by volume of the absorbent material. Hence the absorbing capacity is large. However, absorbents may never be re-used

  • adsorbent type, will attract moisture, onto the total surface area of the desiccant. Hence the capacity is a factor of exposed total surface area of the desiccant. This type of dryer has smaller capacity compared to absorbents, but it can be re-used as the moisture will only be trapped on the surface area of the desiccant

Filter dryer and receiver in a single packageSpecific desiccants that are widely used in air conditioning system’s filter dryer, are silica gel (adsorbent), molecular sieve (adsorbent), lithium chloride (adsorbent), and lithium chloride (adsorbent).

The trade name for molecular sieve is zeolite, and its chemical name is sodium/potassium alumininosilicate. This desiccant goes by the name of XH-5, XH-7 and XH-9. XH-7 and XH-9 are suitable for widely used R-134a refrigerant.


The construction principle:

Filter will be placed at the entrance of the filter dryer component, followed by a pack of desiccant, up until the outlet of the component.

This way, particles will be trapped before dried.

Receivers will have short inlet line, and the outlet line will be dipped into liquid refrigerant. Refrigerant will be pushed towards expansion device, by the pressure within the receiver.

Filter dryer, without receiverA sight glass, downstream of the filter dryer is required, to monitor for any moisture presence in the system. Moisture presence may be detected by formation of water condensation at the sight glass.

These parts, may come in separate packages, or grouped to form a single equipment.


Do we really need filter dryer and receiver?

Hermetically constructed compressors and other air conditioning equipment may not require this.

However, there will be cases of refrigerant leakage, compressor fail, and so on, which will require us to at least remove defective equipment and service. This will introduce moisture into the system.

Breakdowns are inevitable. Maintenance and equipment dismantling are unavoidable, and saturated liquid feed to expansion devices is very important. Moisture ingress is highly likely.

Hence, most air conditioners need filter dryer, and receiver as part of the air conditioner equipment.



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