There are four main types of driers found in AC systems. They can be identified based on their location in the system.
- Accumulator – located in the circuit between the evaporator and the compressor in a system using an orifice tube as the expansion device – a typical cycling clutch orifice tube system (CCOT).
- Receiver – located in the circuit between the condenser and the thermal expansion valve (TXV).
- Sub-cool Receiver – located between the second to last pass and the last pass in a parallel flow condenser.
- Desiccant Bag or Cartridge – same location as #3 but used to service parallel flow condensers with receiver tanks that are brazed permanently to the condenser.
Accumulator Receiver Sub-cool Receiver Desiccant Bag
In order to properly service an AC system and return it to near factory condition each component should be cleaned of all residual oil and debris before re-assembly, evacuation, and recharge. Since it is impossible to clean a drier one should always replace them.
Driers have a limited capacity for absorbing and retaining moisture and once they are saturated they cannot protect the refrigerant circuit. Most driers also incorporate a filter screen which traps debris from other components such as normal wear particles from the internal parts of the compressor.
Another reason for replacing the drier when a system is serviced is to remove contaminated refrigerant oil they have collected. PAG oil that is saturated with moisture or other contaminants will not provide proper lubrication for the compressor.
In actual practice drier types 3 & 4 are always used in systems which have parallel flow condensers (PFC). Since these condensers cannot be cleaned they often require replacement and the new condenser will generally be supplied with an attached drier. For more information about these types of condensers please refer to the tech tip titled “Condensers with Integrated Receiver Driers”.
Our last tech tip reviewed the evolution of condenser designs and discussed why parallel flow condensers trap debris from a worn or failed compressor. Severe contamination of a parallel flow condenser can reduce the capacity of the condenser and restrict oil circulation that is vital to the life of the compressor. In this tip we will review some of the considerations when servicing the attached/integrated receiver driers which are now common place in both domestic and import applications.
All system applications which use a thermal expansion valve (TXV) to control refrigerant pressure in the evaporator also incorporate a receiver drier in the circuit. In an effort to reduce space and mass while providing improved performance, newer sub-cool condenser designs have integrated receiver driers which are located between the last two passes of the condenser. Some sub-cool designs have detachable receiver driers which can be replaced as a component. See photos below.
Condensers with detachable Receiver Drier
Other designs have receiver driers that cannot be detached and are serviced by removing a plug from the lower end of the receiver. Service kits include new a new plug, desiccant bag, and filter. See photos below.
Condenser with serviceable Receiver Driers
Regardless of whether the receiver drier is detachable or serviceable, in most applications the condenser must be removed from the vehicle to service the receiver drier. If the condenser is mounted to the radiator it may also be necessary to remove the cooling module and, in severe cases, bumper covers and grills have to be removed to provide access to service the condenser.
Furthermore, as discussed in our last tech tip, parallel flow condensers cannot be cleaned effectively. If the condenser is a sub-cool design like those shown in the above photos, a new replacement condenser will generally include a new receiver drier as part of the assembly. Because of the probability of condenser contamination and the part/labor cost related to servicing an integrated receiver drier, replacement of the condenser/receiver drier assembly is the best overall repair strategy whenever a new compressor is installed.
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