Dlagnosnganuning probem Again, the ideal situation is to assume each circuit is equally loade Ment amount of heat: however. this situation There are several reasons why circuits can become unevenly esign: In this case, each circuit is not of more circuit(s) ibution: This problem je to the T the individual cicu temperatures and the passageways of feeder tubes, unequal feeder tube lengths, and/or evaporator is reduced in le the other coil fing eas while increased in other areas. Dirty coils or damaged tighly superheated, and thus highly inefficient. COnocung the problom c,如 he problem can only be compens e tips far correcting o compensating for an imbalanced heat na t he case f there are or, three. mpe, egi cr Ib farther downstream on the mixing of5 Why circuits get loaded unevenly Again, the ideal situation is to assume each circuit is equally loaded and absorbs an equivalent amount of heat; however, this situation does not always occur. There are several reasons why circuits can become unevenly loaded. Poor heat exchanger design: In this case, each circuit is not of equal length and loading. Poor refrigerant distribution: This problem occurs due to the wrong choice of distributor or feeder tubes, partially blocked passageways of feeder tubes, unequal feeder tube lengths, and/or kinked feeder tubes. Uneven airflow: Airflow across the evaporator is reduced in some areas while increased in other areas. Dirty coils or damaged coil fins can have a similar effect on airflow. Diagnosing a hunting problem Diagnosing a hunting problem due to an imbalanced heat exchanger requires measuring the exit temperature of each circuit upstream of the suction manifold. To perform this process, average the temperatures of all of the circuits upstream of the suction manifold and compare this average temperature to the actual temperature of the suction manifold close to where the bulb is mounted. If the average value of the circuit exit temperatures exceeds the actual suction temperature value by more than 2°C, then there is probably one or more circuit(s) which are not completely superheated (flooding). A closer examination of the individual circuit temperatures and the associated suction pressure should reveal which circuit(s) are causing the problem. One simple rule to remember is that the valve’s response will favor the circuit that is flooding. Because of this favorable response, a heat exchanger can be operating at a reasonable exit superheat but still have a significant loss in capacity, because the expansion valve is responding to one or more flooding circuits while the other circuits remain highly superheated, and thus highly inefficient. Correcting the problem This can be a difficult task. First, the service tech must recognize the cause of the problem. If not, the problem can only be compensated for and this could mean a reduction in system performance. Here are some tips for correcting or compensating for an imbalanced heat exchanger: If possible, examine and correct any problems with airflow, coil circuitry, and distribution so that the circuits are more evenly fed and loaded. The goal is a more consistent circuit exit temperature on all circuits. One lightly loaded circuit may be tolerable if there are, for example, eight circuits. However, this is probably not the case if there are only three. Adjust the superheat of the valve to a slightly higher value. Attempting to control an evaporator near to or lower than 5癋 operating superheat can exceed the sensing capability of most expansion valves and result in hunting and subsequent intermittent flooding. If practical, move the bulb farther downstream on the suction line.Better mixing of the refrigerant prior to the bulb can smooth out the valve response, although capacity and efficiency may not improve significantly