September Tech Challenge – Answer
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A commercial rooftop utilizing R-410A with a fixed feed device has the customer complaint of “no cooling.” The symptoms confirm inadequate cooling and the condensing unit and blower appear to be running all the time and the thermostat is not satisfied. What are the “possible causes” (Note: There is only one problem intended) with the following measured conditions on this field service check sheet?
Answer: The possible problem appears to be a system overcharge. The overcharge would cause high head pressure/temperature and condenser split because the condenser is nearly filled with liquid refrigerant thereby reducing the effective size (area of heat transmission) of the condenser. The condensing pressure/temperature, and condenser split are high to expel the heat gained in the evaporator, superheat, and compressor. The high compression ratio is causing recompression, high discharge temperatures, and high amperage. The subcooling and superheat are high to normal because the TXV is attempting to maintain a constant S.H. with a lower refrigerant flow caused by the higher compression ratio.
Posted In: Tech Challenge
