Overview
This lesson covers three types of refrigerant compressors commonly used in residential and light commercial HVAC systems: rotary, scroll, and reciprocating compressors, including identification methods and internal mechanisms.
Compressor Comparison
| Type | Shape (Top View) | Discharge Location | Common Applications | Key Features |
|---|
| Rotary | Round | Top | Window AC units, RV units, mini-splits, inverter systems | Factory-mounted accumulator on suction line; thermal overload protector |
| Scroll | Round, tall | Side (upper) | R22 and R410A air conditioning systems, newer high-pressure refrigerants | No direct accumulator; hoisting bracket for installation |
| Reciprocating | Oval | Varies (higher or lower on side) | Air conditioning, refrigeration systems | Stem valve on refrigeration models; piston-based compression |
Rotary Compressor
- Round shape when viewed from above; discharge tube positioned on top of unit
- Electrical compartment located on top; may include thermal overload protector for circuit protection
- Thermal overload opens electrical circuit when compressor overheats to protect windings
- Factory-installed accumulator piped into suction line prevents liquid refrigerant from entering compressor
- Compression mechanism uses spinning rotor that pushes gas from suction through tiny hole to discharge
- Gas enters suction port, rotor spins and compresses it, then pushes compressed gas out discharge line
- Oil stored at bottom of compressor housing for lubrication during operation
Scroll Compressor
- Round and tall when viewed from any angle; discharge tube on side near top
- Suction line positioned separately from discharge; electrical compartment on side of unit
- No factory-mounted accumulator, but suction accumulator can be added externally if needed
- Hoisting bracket (C-clip mount) attached for lifting compressor during installation or removal
- Internal pressure relief valve dumps high pressure back to low pressure area when needed
- Compression uses two scroll elements: one fixed, one oscillating to compress refrigerant gas
- Oscillating scroll moves against fixed scroll, progressively reducing gas volume until discharge through top
- Greater surface area compared to rotary design provides efficient compression
- Vapor refrigerant occupies same space as electrical windings (burnout risk area)
- Oil pumped through internal hole to lubricate scroll compression area
Reciprocating Compressor
- Oval shape when viewed from above distinguishes it from other compressor types
- Stem valve on side indicates refrigeration system use; AC systems use simple suction pipe
- Larger AC models position suction line higher and discharge line lower on housing
- Discharge and suction line positions vary between different compressor models and manufacturers
- Uses piston mechanism similar to car engine with crankshaft and cylinder arrangement
- Single piston in small compressors (refrigerators); multiple pistons in larger units (4-ton heat pumps)
- Suction gas surrounds electrical windings before entering compression cylinder
- Piston compresses gas inside cylinder; compressed gas exits through discharge line
- Crankshaft drives pistons in reciprocating motion (in and out) to compress refrigerant gas
Key Terms & Definitions
- Thermal Overload Protector: Safety device that opens electrical circuit when compressor overheats
- Accumulator: Component that prevents liquid refrigerant from entering compressor suction
- Burnout Compressor: Failed compressor where electrical windings have overheated, leaving black residue
- Stem Valve: Service valve mounted on refrigeration compressors for maintenance access
- Internal Pressure Relief: Safety valve that releases excess high pressure to low pressure side