- It reverses the direction of compressor rotation to prevent damage during startup
- It switches refrigerant flow direction so the system can operate in both heating and cooling modes
- It reverses the polarity of the thermostat signal during defrost cycles
HVAC Exam Topic Library
Master the HVAC Core Curriculum
Every exam domain broken into focused study topics with practice questions and plain-English explanations.
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EPA 608 Certification
Study EPA 608 for your HVAC exam. Covers Core, Type I, II, and III requirements, refrigerant regulations, recovery procedures, and common exam mistakes.
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EPA 608 Certification
Study EPA 608 for your HVAC exam. Covers Core, Type I, II, and III requirements, refrigerant regulations, recovery procedures, and common exam mistakes.
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Refrigeration and Air Conditioning
Study refrigeration and air conditioning for your HVAC exam. Covers the refrigeration cycle, superheat, subcooling, metering devices, and heat pump operation.
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Heating Systems
Study heating systems for your HVAC exam. Covers gas furnace operation, heat exchanger safety, combustion analysis, venting categories, and hydronic heating.
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