November Tech Challenge— Answer
A commercial rooftop utilizing R-410A with a TXV feed device has a customer complaint of insufficient cooling. The symptoms confirm inadequate cooling and the compressor appears to be short cycling. What are the “possible causes” (Note: There is only one problem intended) with the following measured/calculated conditions on this field service check sheet?
Answer: The problem appears to be non-condensable (air) in the system causing the unit to cycle on high head pressure control. If air entered the system or was not evacuated, it will accumulate in the top of the condenser reducing the effective size of the condenser causing high head pressures and high discharge temperatures caused by high compression ratios. Higher condensing subcooling and split will result because of the elevated condensing temperatures. With a TXV the evaporator side (pressures and superheats) will be normal to a little higher unless the pressures exceed the range of the valve. The amps are high because of the higher compression ratios causing the compressor to work harder.
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