Liquid-Line Restriction
A liquid-line restriction could be caused by:
A plugged liquid line drier
A kink in the liquid line
A solder joint filled with solder
A liquid-line restriction reduces the amount of refrigerant to the metering device.
The suction pressure will be low.
The suction superheat will be high.
The discharge pressure will be low because of the reduced load on the compressor.
Liquid subcooling will be high.
The liquid refrigerant will accumulate in the condenser.
It cannot flow out at the proper rate because of the restriction.
As a result, the liquid will cool more than desired.
The amperage draw of the condensing unit will be low.
Plugged Fixed-Bore or Capillary-Tube Metering Devices
A plugged fixed metering device will cause part of the coil to be inactive.
The system will then be operating with an undersized coil.
The suction pressure will be low because the coil capacity has been reduced.
The reduced amount of vapor produced in the coil and resultant reduction in suction pressure will reduce:
Compressor capacity
Discharge pressure
The flow rate of the remaining active capillary tubes
The suction superheat will be high.
The discharge pressure will be low.
The liquid subcooling will be high because the liquid refrigerant will accumulate in the condenser.
The unit amperage draw will be low.
The possibility of moisture in the system that freezes and plugs the capillary orifice should be considered.
Plugged TEV Feeder Tubes
A plugged feeder tube reduces the capacity of the coil.
The coil cannot provide enough vapor to satisfy the pumping capacity of the compressor, and the suction pressure balances out at a low pressure reducing:
Compressor capacity
Discharge pressure
The flow rate of the remaining active capillary tubes
The suction superheat will be in the normal range.
The discharge pressure will be low.
The liquid subcooling will be high because the liquid refrigerant will accumulate in the condenser.
The unit amperage draw will be low.
Suction-Line Restriction
A suction-line restriction could be caused by:
A plugged suction-line strainer
A kink in the suction line
A solder joint filled with solder
It results in a high-pressure drop between the DX coil and the compressor.
The suction pressure will be low.
The superheat will be extremely high.
The discharge pressure will be low.
The amperage draw of the condensing unit will be low.
Be aware that the symptoms listed above usually indicate a refrigerant shortage.
Hot-Gas-Line Restriction
The discharge pressure measured at the compressor outlet will be high.
The discharge pressure measured at the condenser outlet will be low.
The suction pressure will be high.
The DX coil superheat is high because the suction pressure is high.
Liquid subcooling is in the high end of the normal range.
The compressor amperage draw will be above normal.
If the discharge pressure is only measured at the condenser outlet, the symptoms can be easily misinterpreted.
Low-Capacity Compressor
This is the least likely problem.
Determining the age of the unit may be useful, as an older compressor is more likely to have a reduced efficiency.
When the compressor will not pump the required amount of vapor, the suction pressure will balance out higher than normal.
The DX coil superheat will be high.
The discharge pressure measured at the compressor outlet will be low.
Liquid subcooling will be low.
The amperage draw of the condensing unit will be extremely low, indicating that the compressor is doing very little work.
This was the end of troubleshooting learning modules.