Compressor Failure in Newly Installed Rooftop Unit.
The site installed a new 25-Ton gas electric roof unit serving a media center at a private school. The RTU is equipped with several features including air side economizer, hot gas reheat, and demand control ventilation. One of the two compressors failed shortly after being put into operation.
HRG worked with the installing mechanical contractor to diagnose the system and determine the cause of the compressor failure. Some common reasons that a compressor will fail include:
Blockage of Condenser Coils.
Evaporator Motor Displacement.
Low Refrigerant Levels.
Too Much Refrigerant.
Lack of Lubrication.
Clogged or Damaged Suction Lines.
Dirt & Debris Stuck in the Outdoor Unit
Incorrect Sizing of Suction Lines
A comprehensive review of the system determined that the cause of the failure was a manufacturing defect that caused a low refrigerant condition. This is uncommon in newly installed packaged rooftop units because the factory charges the refrigerant system at the factory and most new systems are equipped with a low-pressure safety switch that will disable the compressor when a low refrigerant condition is present.
In this case, the lack of refrigerant led to compressor burn out because it caused an increase in temperature in the compressors motor windings. As the temperature increases, the insulation on motor windings become compromised. This causes a loss in its electrical resistance, a short to the ground, as well as an open winding. High temperatures can also cause the oil to break down, and as such, the lubrication provided will be insufficient, which increases friction within internal components.
After repairing the source of the refrigerant leak, the compressor was replaced and the system was put back into operation. The compressor replacement included:
Testing the Refrigerant
An acid test has to be carried out on the refrigerant using the correct oil test kit to ascertain if it is acidic.
The refrigerant was slightly acidic, use a suction filter dry-out kit to clean the system.
Flush the System
The aim is to remove winding insulation, burned oil, and other contaminants from the system. There is also a need to remove the TXV to prevent contaminants from being flushed into it.
On the same note, the evaporator and condenser need to be flushed in order for the flushing agent that comes out, in the end, to be as clean as possible. This process can be repeated in all refrigerant lines to ensure that residual oil locking contaminants are removed from the system.
If contaminants are not removed, they could plug up the unit and thereby contaminate the oil in the newly installed compressor. Also, check the water flow through the condenser loops and pass a descaler through the condenser loops.
Pump out the refrigerant
The refrigerant needs to be pumped out. Likewise, if the system was not acidic, but has been adequately flushed, you can install a liquid line drier with activated alumina as well as a molecular sieve desiccant.
For instance, install a catch-all filter-drier in the suction line, an access valve on the gauge port, and oversized liquid-line drier in the liquid line.
On the other hand, if the system was not acidic on testing, you need to install a suction line and acid removing drier.
The latter is also required if the refrigerant in the unit is chlorinated. This could cause the acid it produces to cling to the insides, thereby making it difficult to be removed.
Replace the Compressor
Here, you can now replace the compressor.
However, you will also need to pump down the system for 24 hours to create a deep vacuum.
Then, the system can be recharged using a virgin refrigerant.
Perform System Checks
After compressor replacement, you need to let it operate for 24 hours.
Then, you can check its acid and pressure drop across the suction drier core.
The system can be left to run for 48 more hours before the acid is rechecked. If there is no acid present, you can proceed to install a standard core as a replacement to the acid core.
Despite this, the unit has to be checked frequently to ensure that there is no acid. If that’s the case, you can proceed to install a felt element in the core and remove the filter.
The system may be up and running, but a good practice is to perform system checks regularly.
It will ensure that the lifespan of the unit is long, and you can easily find the signs in faulty compressors if any is evident
The contractor replaced the compressor and was able to get the unit running again. This project was completed in 2022.