A/C Fundamentals Flashcards
What is comfortable air temp?
70-75 F
21-25 C
What is comfortable humidity level?
40-45 %
What is purpose of HVAC system?
Provide exchange of air
Control humidity
Heat and cool cab
Allow filtered fresh air to enter
Heat intensity
Also called sensible heat. Measured in temperature
Heat quantity
Amount of heat energy, measured in BTU’s
Latent heat
Is the energy that is required to change the state of a substance without changing the temperature.
Superheat
After latent heat of evaporation, when the refrigerant continues to absorb heat energy, however the vapour ref. will only increase in temperature and not pressure.
TPT-SAT = S/H, measured at lowest low pressure
Subcooling
Occurs after latent heat of condensation, ref. continues to give off heat energy with no change in pressure.
SAT-COT = S/C, measured at highest high pressure
TXV specs
H/S pressure : 2-2.5 x amb temp
L/S pressure: CC - 15-30 PSI, VD - 29 PSI
S/H: 6-12 F
S/C: 10-20 F
Orifice tube specs
H/S pressure : 2-2.5 x amb temp
L/S pressure: CC - 20-45 PSI, VD 29 PSI
S/H: 0-4 F
S/C: 10-20 F
R134A
Tetrafluoroethane
HFC
Light shy blue container
Mineral based A/C oil
Used with R12, amber in colour
polyol ester POE
Used with all ref., clear in colour
polyalkylene PAG
Used R134A only, light blue in colour
What two ref. oils do not mix?
PAG and MIN
Expansion
As refrigerant travels through the metering device, it expands and the pressure is dropped.
Evaporation
Because the pressure has been dropped the liquid ref. undergoes a state change to a vapour. As the change occurs latent heat is absorbed from the surrounding air
Compression
Vapour ref. is compressed which adds pressure and temperature to the system.
Condensation
The heat of compression is removed turning the ref. vapours into a liquid
VD compressor
Compressor control valve uses low side pressure to control the swash plate
