HVAC general knowledge Flashcards
What is superheat?
Saturations above boiling point
What is sub cooling?
Temperature below saturation point
How to determine discharge pressure?
Ambient +10-35
How to measure resistance in fan motor?
Using a ohm meter
How to charge unit with fixed orifice?
Using superheat
TXV is charged by?
Subcooling
Run winding reading is.
Lowest .5
Start Winding reading
Is in the middle. 1.0
Common winding reading measures?
Total reading run + start 1.5
What temperature is comfort cooling?
40-50 degrees F
How to determine superheat?
Suction line temperature
=superheat
How to determine sub-cooling?
High side pressure (converted to temp)
-subtracted by
Liquid Line Temp
=sub-cooling
Formula for CFM?
How is velocity measured?
In what situation is Pi used ?
Area x Velocity = CFM
Velocity is measured in FPM
Circle object Pi x radius x2
What does a overcharge indicate in a system?
High head pressure
High sub-cooling
Low superheat
What 2 actions happen in the evaporator?
Latent heat of vaporization
&
Superheat
What 3 actions happen in condenser?
Removal of superheat
Latent heat of condensation
Sub-cooling
How are circuit breakers rated?
In AMPS
Reading voltage across fuse means?
Fuse is bad
Reading voltage drop across contacts while closed means?
Contacts are dirty
If circuit breaker is open and you Ohm out contacts you should read?
OL
How to check MF? (MicroFerrite)
2654 x AMPS x Volts
A good contractor will measure?
Some resistance
Ohms law is?
If AMP draw goes up
Resistance will drop.
How many ohms per volt?
1000
Run compositors are in ? With start windings?
Series
How many BTU per ton?
12000
A closed contact has ?
0 resistance
A single compressor to operate 7evaporators at different temps is?
EPR
Where is the glass sight located?
Discharge line
