In an R-12 system, the sight glass should be clear and colorless.Ī combination sight glass and moisture indicator is essential for easy field maintenance on any system, and is required on any field installed system unless some other means of checking the refrigerant charge is provided.Ī sight glass in a convenient means of determining the refrigerant charge, showing bubbles when there is insufficient charge, and a solid clear glass when there is sufficient charge. The compressor is trying to draw refrigerant from the evaporator through the suction line, but the liquid-line restriction is preventing refrigerant from entering the evaporator.The heart of any air conditioning system is the refrigeration system. Most of the refrigerant will be in the receiver, with some in the condenser. This is caused from the TXV, evaporator, and compressor being starved of refrigerant from the liquid-line restriction. If the system becomes completely restricted, the compressor will pump down the system and stay off, or short-cycle sometimes on the low-pressure control. The severity of the restriction in the filter drier will determine how high the discharge temperature will be.
This is assuming there is still some mass flow rate of refrigerant through the system. High compression ratios from the low evaporator pressure will cause high heat of compressions, thus high discharge temperatures also. Most of the refrigerant will now be stored in the receiver simulating a pumped-down refrigeration system.Ī starved evaporator from the liquid line (filter drier) restriction will cause the high superheats. This small amount of heat to reject will cause a low condensing pressure and temperature. This is simply not the case, especially on a TXVreceiver system.Ī restricted liquid line will starve the evaporator of refrigerant, causing low evaporator pressures. However, any restriction or damage to the liquid line from the receiver outlet to the metering device inlet will have similar symptoms as a restricted filter drier.īecause the filter drier is located in the liquid line, a restricted filter drier can now be referred to as a liquid-line restriction.Īssume, for sake of discussion, that the refrigeration system is a TXVreceiver system employing a filter drier and sight-glass. The liquid line is located between the receiver and metering device (Figure 2). The liquid line is located between the receiver and metering device.įor this purpose I have included a service checklist (Table 1) as well as a number of illustrations.
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