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Defective Equipment is Rarely the Cause of Mechanical Failure

When it comes to HVAC breakdowns, the causes generally fall into two categories. About eighty percent can be attributed to problems with electrical, controls, or associated hardware such as contactors, relays, instruments, and CPUs, and the remaining twenty percent involve mechanical failure. While a small number of mechanical failures are due to defective parts or equipment, most are due to issues like poor design, substandard installation, or lack of maintenance. Mechanical failures are usually the most costly and the most preventable. Most can be avoided through proper installation, startup, balancing, commissioning, and preventive maintenance.

Case in point, multiple air handling units were installed on the roof of a healthcare facility under construction in central New Jersey. These were 100% outside air units with staged DX cooling – not your standard system. Such units require very-specific refrigerant piping and accessories to provide proper refrigerant and oil circulation and call for contractors with intimate knowledge of staging controls for steady discharge air. On this project, piping and controls were handled by installers unfamiliar with this type of system.

Within weeks of installation, four large reciprocating compressors were faulting and failing, and were replaced at great expense. Unfortunately, the HVAC contractor neglected to find out exactly why the compressors had failed before replacing them – a cardinal sin. Again, four new $15,000 compressors failed within weeks. Heads exploded, and MSC was called in to diagnose what went wrong.

MSC technicians found numerous issues with the piping system that had led to incorrect vertical and horizontal refrigerant velocities: missing traps, missing suction accumulators, missing solenoid valves necessary for pump-down, and incorrect controls staging. It was determined that neither the piping contractor nor the controls contractor on the project had the expertise for the system, and the team who did the equipment startup lacked the experience to know what to check for and didn’t recognize problems in plain sight. MSC prescribed the appropriate remedies, and corrections were made to the piping and controls before new compressors were craned onto the roof. Proper startup was conducted, and this time the compressors performed without a hitch.


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