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Deposition Designation Station
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Heating, ventilating, and air conditioning (HVAC) systems consist of many components that work in unison to create the desired comfort level for our homes and offices. A well maintained system is designed to last around 15 years, but the life can be dramatically reduced when proper installation procedures and routine maintenance are not performed.


The HVAC refrigeration system is composed of the outdoor coil, compressor, lineset, metering device, and indoor coil. The compressor is the main component of the system and commonly referred to as the "heart" of the system because it pumps the refrigerant through the coils and the lineset. The inside of a compressor contains a rotor, pump or scroll, and stator (windings) with leads that are connected to the terminals through the hermetic seal. A failed compressor can be observed with a direct short to ground of the windings, a winding to winding internal short, a hermetic seal rupture or a mechanical issue.

The amount of refrigerant or charge in a system can affect the performance and wear on a compressor. Too much refrigerant can cause liquid refrigerant to enter the compressor, which causes mechanical issues. Too little refrigerant can cause the compressor to overheat. A properly charged system allows suction gas to keep the compressor windings cool. The oil is found in the crankcase of the compressor, which provides lubrication to its moving parts. If a system loses its refrigerant and oil then the compressor will cycle on its overload and this can cause the mechanical parts to seize without causing any electrical damage to the compressor's windings. An overload is an internal protection device which measures the compressors internal temperatures and should keep the compressor from failing, but this mechanism can fail if the unit has been operating with an incorrect charge. A service technician can determine if the compressor's internal components have seized using his digital meter and amp probe. This mechanical failure is referred to as locked rotor amps.


The only two things allowed inside of the sealed copper tubing refrigeration system are the refrigerant and the refrigerant oil. Any contaminants like moisture or debris can cause premature compressor failure. A situation called an acid burnout commonly occurs with improperly evacuated systems or poor maintenance practices. Acid occurs in systems when the moisture-contaminated refrigerant is compressed and circulated in the system over a period of time or excessive heat causes the oil to breakdown which then causes the unwanted chemical reaction. A simple acid test can reveal the presence of the unwanted particulates in the system. In the event that the oil loses its lubricating properties along with a breakdown of the compressor windings varnish and insulation, the unit's circuit breaker will trip. The homeowner then summons an HVAC contractor to diagnosis the failure.

Compressors can fail for many different reasons: wear and tear, age, improper installation or repairs, poor maintenance practices, power surge and others. Extending the life of a compressor requires routine maintenance, proper refrigeration practices, and operating the system within the manufacturer's specifications. A properly maintained system involves keeping a clean air filter, keeping the outdoor unit clean, properly charging the refrigeration system, and regularly checking the electrical connections.


Properly diagnosing a failed HVAC system is crucial in determining the appropriate repair. A failed compressor can be very costly to the homeowner and entire systems are changed by contractors because of the failed compressor. Consequently many compressors are condemned by a service technician without determining the actual cause of the failure.

It is important for the technician diagnosing the failure to have specialized training to determine the cause of failure and have the ability to deconstruct the compressor. Donan's Lightning Investigation division determines how compressors and other components of the HVAC system fail and include our findings, repair recommendation and price to repair in an electronic report. We destructively test the compressor onsite to ensure we document an accurate cause of failure and can deliver the report quickly.

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DONAN, a family owned company founded in 1947, provides full-service Forensic Engineering and Fire Investigation Services. For over 60 years, Donan Engineering has been providing unbiased answers to their client's complicated questions. Their team of licensed and experienced forensic experts provides investigative services in the fields of engineering investigations, fire and explosion origin & cause, roofing investigations, and component testing. The diversity of their multidisciplinary staff allows them to provide not only a complete service, but a complete service whose conclusions can be successfully and completely supported.

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