General HVAC Info Study Guide
What power is used in residential HVAC?
120 volts, control circuits are 24v
What power is used in commercial HVAC?
277/480v, control circuits are 24
What does the thermostat do in an HVAC system?
A device that regulates indoor air temperature by sending signals to your HVAC system to either heat or cool.
What state is the refrigerant in when it leaves the condenser?
A high-pressure liquid, after being de-superheated and condensed into a liquid by the condenser.
What does Ductwork do in an HVAC system?
A network of pipes that transport conditioned air from the HVAC system to the air vents that supply the rooms/areas of the building.
What does refrigerant do in an HVAC system?
Absorbs and transfers heat from inside a space to the outside environment. A liquid or gas that helps cool a space when its too warm.
What does the Evaporator do in an HVAC system?
Absorbs heat from the surrounding environment. Converts refrigerant liquid to gas which absorbs heat from the air. Cools the refrigerant down enough to perform heat transfer.
What does an air handler do in an HVAC system?
Blows the warm or cool air into the ductwork to supply the areas of a building with the desired conditioned air.
What does a furnace do in an HVAC system?
Burns fuel (Propane/Natural Gas) to produce heat which is then used to heat the desired space.
What refrigerant identifications are there?
CFC, HFC, HCFC, HFO, HC
What does a condenser do in an HVAC system?
Changes a high-pressure vapor to a high-pressure liquid. 1: Desuperheats 2: Condesating (changing from vapor to liquid stage 3: Subcooling
What does the compressor do in an HVAC system?
Circulates and pressurizes the refrigerant. Allows the refrigerant to absorb heat from indoor air, transfers heat from inside to outside.
What is the refrigerant flow cycle?
Compressor to condenser, condenser to expansion device, expansion device to evaporator, then evaporator to compressor.
what causes low subcooling?
Defective metering device, too little refrigerant, lack of airflow to the condenser, poor compression.
What refrigerant enters and leaves the compressor?
Enters as a low-pressure, low-temperature, superheated vapor. after being compressed it leaves as a high-pressure, high temperature, superheated vapor.
What does an expansion valve do in an HVAC system?
Expands the liquid refrigerant as it passes through the valve which cools the refrigerant.
What type of refrigerant is R-22?
HCFC
Where does refrigerant go after the metering/expansion device?
It enters the evaporator as a low-temperature saturated refrigerant. After absorbing heat, it evaporates into a low-temperature vapor. (Known as direct expansion).
Where does refrigerant go after leaving the condenser? And what state is it in?
It goes to the metering device or expansion device as a high pressure, subcooled liquid.
What causes low superheat?
Lack of airflow to the evaporator, malfunctioning metering system, too much refrigerant, clogged evaporator coil.
How to calculate superheat?
Measure low side pressure on the gauge. Convert pressure to temperature. Measure the suction line temperature where it leaves the condensing unit. Subtract the converted temperature from the suction line temperature.
How to calculate subcooling?
Measure the liquid line temperature before the metering device and where it meets the evaporator. Measure the high side pressure using gauges. Convert pressure to liquid temperature. Subtract the liquid line temperature from the saturation temperature of the refrigerant.
What does a heat pump do in an HVAC system?
Moves heat from one place to another, it uses energy to pull heat from the outside and move it to the inside.
What does psig mean?
Pounds per square inch gauge (Low Side)
What does a humidifier do in an HVAC system?
Produces moist air which is then carried through the ductwork and into your various spaces of your building/house.
Examples of CFC Refrigerants
R-11, R-12
Examples of HFO Refrigerants
R-1234yf
Examples of HFC Refrigerants
R-134A, R-410A, R-404A, R-407c, R-422B
Examples of HCFC Refrigerants
R-22, R-123
Examples of HC Refrigerants
R-600A, R-290
To process refrigerant to a level equal to new (virgin) product specifications as determined by chemical analysis defines:
Reclaiming
To ______ is to clean refrigerant for immediate reuse
Recycle.
High side pressure or Discharge pressure on a gauge manifold is what color?
Red (High Side)
What component takes a low pressure, low temperature refrigerant vapor and turns it into a high temperature high pressure, superheated vapor?
The compressor.
What happens to the refrigerant after evaporating in the evaporator.
The refrigerant is superheated above its saturation temperature and enters the suction line. From the suction line, refrigerant enters the compressor as a low-pressure, low temperature, superheated vapor to repeat the cycle.
What does a heat exchanger do in an HVAC system?
Transfers heat from burning gas or oil and puts it into the air to heat the air, it also vents dangerous flue gases. Heat is transferred in 3 ways: Conduction, Convection, and Radiation
What does the condensing unit do in an HVAC system?
Transfers the heat absorbed from the indoor air to the outside environment, cools the refrigerant using coils outside which are cooled by air passing through the fins and over the coils.
What does a Binary Refrigerant mixture mean?
Two-part mixture
What does an air conditioner do in an HVAC system?
Uses a refrigerant cycle to absorb heat from indoors and move it to a place where it doesn't matter (Outside)
Do most HFCs have a high global warming potential? (Yes or No)
Yes
What does a Ternary Refrigerant mixture mean?
three-part mixture
