HVAC Test 1 Flashcards
What is the purpose of the limit switch located on the heating element?
Limits the power. Keeps it at a safe level.
*From the blower motor shutting down, can’t get any airflow, heating element gets too hot, the house could burn down.
How many BTU is one ton?
12,000
Latent heat of ice?
144
What do we vacuum down to?
29.9 mercury
On the compressor and reading the resistance between run and start but read infinity, OL, common and run and common and start.
Open overload
*If you read resistance on the run winding then it’s not a bad winding.
How do you use an ammeter?
In series
What does the Delta T measure for use?
Return air and supply air
What is an EMF meter?
measurements of ambient electromagnetic fields that are performed using particular sensors or probes.
What keeps the compressor running cool?
Cool Suction line vapors
What does OL mean?
Openline, Open circuit
The winding on the motor are located where?
Stator
What component will energize the compressor located in the condenser?
Contactor
What kind of heat makes a face change but no change in temperature?
Latent heat
*Latin for hidden. Hidden from the thermometer.
42,000 of BTU is how many tons?
3.5 tons
*12,000 BTU’s = 1 ton
42,000 / 12,000 = 3.5 tons
What is a sensible temperature?
The temperature that we can measure.
What is the CFM per ton?
400 CFM per ton
How many BTU’s do you have to remove from the air to face change?
970 BTU per lbs.
Any capacitor run or start is always in what with its windings
In series with the start windings.
Any time you use an ohm meter the power must be set to?
Off position
What kind of magnites to you form when you use electricity?
Electromagnites
When your not calling for cooling on a thermostate between R and Y you are reading what voltage?
Low voltage, 24V
*Except when you are working with refigeration, then you might be dealing with 120 or 240V
How do you condemn a proper grounded compressor?
Put one lead on any terminal and one on the interconnecting piping (copper).
On the compound gauge, on the low side, what does it measure?
It reads above atmospheric pressure (14.7psi)
Low side pressure, Atmospheric pressure, vacuum.
When the liquid refrigerant leaves the condenser and enters into the TXV or any metering control it will enter into the____?
evaporator coil
What do we always purge from our manifolds?
No condensable air
What is Alternating Current (ac)?
Electric current in which the direction of electron flow reverses or switches at regular intervals. 60Hz current, electrons reverse direction 120 times per sec.
How do you measure superheat?
Take the suction line pressure, convert it to temperature minus the actual suction line temperature.
How many terminals for a hermetic compressor usually have and who are they?
3 terminals
1)R-Run 2) S-Start 3) C-Common
How many windings does a hermetic compressor have?
2
How many windings does a 3 phase motor have?
3
If you Ohm the windings of a 3 phase compress, how would they Ohm?
The same. 120 degrees apart.
We use current relays to de-energize start windings and start capacitors. What are other relays used?
Potential Relay also is known as a voltage relay.
Two ways a compressor can fail?
Electrical and mechanical.
What do you have to do for the refrigerant to change its physical state?
Add or remove heat
What is thermodynamics rule #1?
Heat is work and work is heat
What is thermodynamics rule #2?
Heat travels from hot to cold.
What are the terminals of a termostate?
R-Power G-Fan W-Heat Y-Cool C-Common
How do you wire a potential relay?
5-2-1
1) 5 to Common terminal to the compressor
2) Common terminal to compressor
3) 2 to Herm (Start winding) of the capacitor
4) 1 to Start capacitor
Make sure the common to the terminal of the compressor and 5 of the potential relay are both on the same side of the contractor.
Heat can transferred or moved from one body to another by?
Radiation, conduction, or convection.
What is the most common case for a transfromer to burn out?
Shorted low voltage
What has a primary in and secondary out?
transformers
How do we measure capacitors?
Using MFD milliFarad
What does NC mean?
Normally Closed
What does NO mean?
Normally Open
A motor that uses a run capacitor in series with a start winding without using a start capacitor is a?
PSC - Permanent Split Capacitor
note: CSCR uses a start capacitor
What determines the temperature at which a refrigerant will face change?
Pressure
Where are internal overloads located?
Internally in the motor. In the common terminal of the compressor.
