Compressor
The pump at the heart of an AC or heat pump that pressurizes refrigerant so it can move heat. Single-stage compressors are on/off; two-stage and variable-speed compressors modulate output for steadier temperatures, better humidity control, and lower bills.
The longer answer
The compressor is the hardest-working and most expensive component to replace in any AC or heat pump. Single-stage units start and stop constantly; inverter and two-stage compressors match output to actual load, reducing wear and improving efficiency ratings.
Compressor staging directly affects HSPF2 and SEER2 ratings — the federal efficiency numbers that determine rebate tiers. A variable-speed compressor isn't just a comfort feature; it's the hardware difference between an 8.1 and a 9.5 HSPF2 rating on otherwise similar equipment.
The Seattle angle
Inverter compressors in ductless heads are why Seattle homeowners notice the difference immediately — whisper-quiet operation and no temperature sawtooth on mild 40–50°F heating days.
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