RIGID’s compressors are built to order. Prior to installation, compressors should be stored in an upright position to prevent oil from entering the suction or discharge tubes. If compressors are to be stored in inventory for long periods of time, they should be stored in climate chambers or storage areas that can control both temperature and humidity.

RIGID compressors are built with high precision parts that are susceptible to chemical attack and corrosion from contaminants in ambient air. Compressors are always shipped with a low-pressure nitrogen blanket sealed with rubber plugs to maintain this pressure and prevent internal parts from exposure to moisture and other contaminants. If long shelf life is anticipated, it is important to maintain an inert atmosphere to prevent internal corrosion or chemical attack.

All compressors shipped from RIGID are charged with 25cc of RL-32H oil, are evacuated, sealed with low-pressure nitrogen, and capped. In addition to the compressor, other system components should be internally dried, sealed, and stored in an inert atmosphere until installation, preferably no more than 15 minutes from assembling components.

Remove the compressor from its packaging while keeping it in an upright position. Failure to keep the compressor upright can result in the flow of oil into the suction accumulator and process connections, which can cause brazing problems. The compressor must also remain upright while assembling the grommets in the mounting bracket to the base plate.

The cleaning and removal of solid substances and non-condensible and the removal of moisture and other gas contaminants in all components of the refrigeration system are key to successful compressor operation and long life. In addition, the use of R134a with new polyolester oils has been accompanied by new stricter standards in comparison with CFC or HCFC refrigerants. Any non-compatible products that can contaminate these refrigerants and polyolester oils including chlorine compounds and non-ester-based oils need to be eliminated. Other system components such as tubing, evaporators, condensers, receivers, valves, capillaries, and separators need to have these contaminants removed before the system is assembled.

RIGID recommends that all components remain sealed as long as possible before assembly, performing the brazing no more than 15 minutes after exposure to ambient.

It is important to avoid residual oil during brazing by blowing out components with nitrogen or dry air, with a dew point lower than -40ºF. Internal oil on surfaces of the suction or discharge tubes can cause difficulty in brazing, and even more hazardous, it can introduce contaminants into the system from ‘cracking of oil’.

The filter drier needs to be protected from absorption of ambient humidity during assembly of the system components using the following practices:

• Remove protective caps just prior to brazing.
• For filters supplied without protective caps in hermetic boxes, these must also be protected to avoid moisture absorption before.

If the drier does not have complete water absorption in the molecular sieve, then moisture can circulate freely in the system with the following effects:

• Ice Buildup: Reduces the cross-sectional area of a capillary tube or TX valve.
• Acid Buildup: Causes serious attack in compressor and to the molecular sieve in filter drier.
• Oil Contamination: Acidification reduces lubrication, changes oil color, a  buildup of sludge, and poor lubrication of the compressor.

RIGID is not responsible for damage to its compressors from the introduction of such contaminants.

RIGID compressors have been designed and tested for operation with R134a refrigerant. Some users may want to employ other refrigerants or refrigerant blends, and other refrigerants may perform quite well. However, due to case design pressure considerations, refrigerants that have a maximum working pressure greater than 350 psi (24.13 bar) are not recommended. If other refrigerants are to be used, the compressor should be thoroughly tested and evaluated with those refrigerants to verify reliability with expected conditions in the intended application. Because of the wide differences in refrigeration systems with different working fluids, the reliability of all equipment should be evaluated for appropriate life through field tests.

Rotary compressors perform best when the pressure ratio between the high and low sides of the compressor is less than 8:1. When the pressure ratio exceeds this value, the compressor’s coefficient of performance (COP) is adversely affected. Good refrigeration practice requires that careful evaluation of the refrigeration system and evaporator conditions be specified and that an appropriate refrigerant is selected to avoid excessive pressure differential.

12.1 R134a Refrigerant

R134a (tetrafluoroethylene) is a replacement for R12 in applications with medium and high evaporator temperatures in Aspen’s compressors. Its physical properties are: Molecular Weight – 102

Critical Temperature – 101.1ºC Critical Pressure – 40.6 bar Boiling Point -26.5ºC

This refrigerant also requires the exclusive use of polyolester oil (POE) as a lubricant. R134a refrigerant is associated with strict requirements for the internal cleanliness of the cooling system. In addition to chlorine and water, solid residues must be carefully removed including dust, metal particles, etc., which can damage the compressor. The recommended lubricating oil is POE RL 68H. This lubricant is highly hygroscopic (water absorbing) which can cause the formation of acid residues. When present, these acid residues can create a blockage in the capillary tube and reduce lubricity in the compressor.

The level of moisture in the refrigeration system should be below 40 ppm. It is recommended that a filter dryer compatible with R134a and POE be installed with the capability to remove moisture from the system to below 20 ppm. The compressor and other components should remain sealed until they’re ready to use. The compressor and other system components should not be open to the ambient for more than 15 minutes. Good refrigeration practice also calls for system evacuation of both low and high sides, achieving a minimum vacuum level of 0.14 bar (100 ! Hg).

12.2 Refrigerant Charge

Following the system evacuation, it must be charged with refrigerant. For a low-capacity system, as little as 40 grams might be used, while as much as 120 grams might be used in a high-capacity system. After the refrigerant is pumped into the system, it is wise to wait 5-10 minutes before starting the compressor to allow refrigerant evaporation and avoid the ingestion of liquid into the compressor. For high charge levels, the system should be equipped with a liquid receiver. An accumulator should always be used with rotary compressors to minimize liquid intake in the compressor.

12.3 OIL MANAGEMENT

Even the most experienced refrigeration technicians need to read these instructions carefully since the quantity of oil used in RIGID compressors is much less than found in other types. Some lubricating oil will travel with the refrigerant in any refrigeration system. Thus, it is imperative that they be miscible and fully soluble in one another at all temperatures. This provides good oil return and lubricity for the compressor while avoiding heat transfer losses in the evaporator. During the prototyping of the refrigeration system, it is vital that the proper amount of oil in the system be determined. RIGID compressors are all shipped with 25cc of POE RL 68H. This has been found to be adequate for many compact cooling systems.

There is no sight glass to visualize oil flow within the compressor. Therefore, the following procedures are highly recommended to ensure that adequate oil is present at all times. Keep in mind that oil entrainment occurs in all compressors, and typically is a function of compressor speed (RPMs). All RIGID cooling systems have been designed to be fully drainable with no traps in heat exchangers, and contain a refrigerant refill valve where coolant or oil can recharge.

12.4 Oil Charging

Using a syringe (see photo below) load the compressor with adequate (RL 68H, Viscosity: 300SUS, recommended or equivalent) refrigerant oil through the discharge port. Make sure the syringe is inserted just far enough to reach the inner chamber to allow air to purge but not to contact internal electrics, which might cause damage.