Most blends operate at higher compression ratios and at different temperatures than the refrigerants for which the compressors were designed to operate.
Refrigeration systems are designed initially for a specific refrigerant. These changes can bring about some problems in the system.
When a blend is used, the condenser and evaporator that were sized for the original refrigerant may not be able to handle the additional loads placed on them by the higher- temperature, higher-pressure blends.
Superheat, subcooling
Often the condenser does not have the capacity required to provide the proper subcooling; in this case, provisions may be needed to increase condenser capacity. Changing the capacity of the metering device may also need consideration.The temperature of the return gas from the suction line (superheat at compressor) determines the internal temperature of the compressor, making it imperative that the temperature of the suction gas be controlled. Increased loads on the condenser can indirectly affect the return gas.
Equally important is the discharge gas temperature; measuring discharge temperature gives a good indication of whether the suction gas is cool enough to keep the compressor windings from overheating.
Temperatures lower than 225°F 6 in. from the compressor on the discharge line are acceptable. However, any temperatures higher than that can cause the breakdown of the oil in the system.
In short, if the amount of refrigerant entering the compressor is controlled, the condenser load can be lowered, subcooling can be increased, and superheat at the compressor can be lowered.
All these temperatures and pressures, properly monitored, can extend compressor life with any refrigerant.
Nohle is with Nohle Refrigeration Supplies, a Division of Meier Supply, Binghamton, NY; 800-338-3200; 607-724-2451. Got a good hvacr service tip? Send it to Barb Checket-Hanks at The News: checket-hanksb@bnp.com (e-mail); 248-362-0317 (fax). The best tips will run in upcoming issues of The News.
