Compressor Facts and Troubleshooting (Don Gillis / Trevor Matthews)
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When troubleshooting compressors, Emerson’s mobile apps are some of the best tools you can have in your arsenal. Those apps include the AE Bulletins, Copeland Mobile, HVACR Fault Finder, and White-Rodgers Mobile. These apps contain information about compressors and controls, and they even have troubleshooting maps and tools to assist you with diagnosis in the field.
The Copeland Mobile Lab is a database for all Copeland compressors, and its mobile app can direct you to a wide range of facts, including weight, dimensions, oil, winding resistance, etc., based on the compressor model number and serial number. The app also comes with a calculator that allows you to enter the operating conditions and see how the capacitor, current, and discharge temperature change based on the evaporator and condenser temperatures. You can also view the part numbers for accessories.
The AE Bulletins app contains all of the Application Engineering bulletins and notifies users of updates to the bulletins over time. You can also search for bulletins with keywords and access bulletins based on the equipment type (divided into specific sections for compressors, condensers, accessories, etc.). The app also contains an FAQ page and information about retrofit procedures and appropriate refrigerants and oils for each compressor.
Semi-hermetic Copeland compressors come in two main varieties: Copelametic and Discus. Copelametic (Reed) compressors may be replaced with Discus compressors, but the opposite isn’t true. Both types have accessible construction, four-pole motors, cast-iron bodies, and positive displacement oil pumps. However, the oil cup and flinger may vary by individual model. These compressors use reciprocating pistons to compress the vapor refrigerant. Valve plates differ between Copelametic and Discus compressors, with the latter being less prone to overheating. Discus compressors also have minimal reexpansion and come in digital varieties to reduce cycling, making them very efficient.
Many Copelametic (Reed) compressors are air-cooled; air passes over the compressor body to keep the compressor cool. On the other hand, water-cooled compressors use a water jacket to cool the compressor (but these can be replaced with air-cooled compressors). Refrigerant-cooled compressors rely on suction gas to prevent overheating. Compressors may come with a deep sump or a flat bottom. Discus compressors may also come in short-head or tall-head models and can be adapted for the other head size.
Copeland also manufactures scroll compressors for medium and low-temp applications. These Scroll compressors have two main parts: a fixed scroll and an orbital scroll. The orbital scroll oscillates and compresses the gas, and the compliant scroll design allows the scroll to be a bit more tolerant of liquid. These compressors also have a floating seal and motor protection. Copeland has developed a two-stage scroll and a digital scroll, which allow for modulation to match loads more accurately.
You can add VFDs to any fixed scroll or Discus compressor to achieve the capacity of variable-speed systems. Copeland also carries variable-speed scroll compressors.
Compressors generally fail more often due to mechanical reasons than electrical, though many people assume the opposite. Overheating, floodback, contamination, slugging, and flooded starts are the main mechanical causes of failure. These may result in damage to the bearings or pistons, which ultimately leads to mechanical failure. Finding the superheat and following the manufacturer’s guidelines can help you prevent floodback, which washes out the oil. Check for oil foaming and other signs of wear, too. You can prevent flooded starts with crankcase heaters. Oil slugging can also happen due to severe migration, floodback, or uncontrolled oil return, and it may lead to broken wrist pins, pistons, and rods. Overheating may happen due to excessive refrigerant temperatures or oil loss, and you can prevent it by maintaining the charge and compression ratio (or using additional cooling when required). To prevent contamination, pull deep vacuums and clean the system out ENTIRELY after a burnout.
Trevor and Don also cover:
- Emerson brands, divisions, and technologies
- Wholesaler relationships
- Oil lubrication
- Valve plate configuration
- Reed-to-Discus compressor replacements
- Miscellaneous compressor valves
- Axial vs. radial compliance
- Appropriate digital compressor applications
- Replacement practices
- Setting low-pressure controls
- Blow by test
- CoreSense and Centronics
- Demand cooling
- Oil sight glasses and safeties
- Copper plating
- Troubleshooting questions