313D Exam -V5 (Complete) Flashcards
If a technician discovers a 30,000BTU system installed on a GFA075….
The technician should consider improving the ductwork- acheive a lower static pressure.
With a 2.5 ton system you need ideally 1000 cfm.
The equalizer line on TXV is generally 1/4 OD, it connects to the..?
Suction line and conveys evaporator to the bottom of the valves diaphragm, giving a closing influence to the valve.
What gauge of wire should be used for a condensing unit that is rated for 25 amps and the total wire length is 105 ft?
6 awg
If a metering device is too restrictive….
- Superheat will increase
- Suction pressure will decrease
- Subcooling will increase
- Head pressure will increase
What system pressure would be typical for the following conditions?
Refrigerant= R22
Metering = Orfice
Indoor= 85F DB, 79F WB
Outdoor=75F DB, 66F WB
80/240 PSIG
Besides low refrigerant, what are some thigs that cause evaporator freeze up?
Airflow-Clogged secondary evaporator
Open damper on bypass humidifier
Airflow- Undersized furnace blower motor
What can cause high compressor amperage?
High humidity,
The OHM reading taken from a hermatic compressor are;
12 ohms from R to ground,
6 ohms from S to ground,
18 ohms from R to S,
6 ohms fro R to C,
and 12 ohms from S to C
There’s a small short to ground halfway through the start winding.
R to Ground tells you its completely going through the runn winding.
What will be the approximate R22 liquid pressurea at the metering device inlet if the liquid line rises 20 ft and the pressure at the condenser outlet is 200PSIG?
100F
189
Assuming your losing .55 psi per foot
20ftx 0.55psig drop
True or False
Evaporator saturation should be colder than the suction line.
True
True or False
The liquid line should be warmer than condenser saturation.
False, it will be cooler.
True or False - Typical single phase induction motors have a start winding which is automatically disconnected shortly after start up
True
Thermal radiation is…
The transfer of heat energy through electromagnetic waves
Thermal convection is…
Heat causing the flow of vapour or liquids due to differing densities
Thermal conduction is..
The transfer of heat energy through molecular vibration, contact, collision
The cooling anticipator is wired in series with…
The coil of the compressor contactor
Motors briefly during startup draw highest amperage through which winding?
Draw highest amperage through the run winding
What is the pressure inside a newly filled N2 cylinder?
2350 PSIG
N2 = Nitrogen
Which of the following is a vacuum measurement?
1. 29.9 PSIA
2. 29.9 “ Hg
3. 29.9 PSIG
29.9 “ Hg
At what temperature will the fins on an evaporator begin to sweat if the air in contact with it is 75F DB and 63F WB?
56F
Which refrigerant became an industry accepted replacement for R22?
R410A
Why is a “fan control centre” added to an older furnace during the installation of a new air conditioner?
- Because the furnace does not have a blower relay
- Because the furnace transformer is of insufficient VA for the compressor contactor
The force that drives a reversing valve to shift is?
The system pressures
A TEV that is stuck nearly shut will cause high or low suction pressure?
Cause low suction pressure
Air conditioning high head pressure can be caused by?
- High humidity
- Non condensables
- Clogged condenser coil
On a TXV high side pressure exerts a(n) ____Influence on the valve
Opening
The TXV spring exerts a(n) ____Influence on the valve
Closing
On a TXV evaporator pressure exerts a(n) ____Influence on the valve
Closing
A TXV sensing bulb exerts a(n) ____Influence on the valve
Opening
Which of the following will cause liquid refrigerant to build up in the condenser? (2 answers)
1. Poor evaporator air flow
2. Failed condenser motor
3. Cold condenser ambient
4. A metering device that is too restrictive
3.Cold condenser ambient
4.A metering device that is too restrictive
When fresh air from outside is brought in for ventilation purposes…
- It must be filtered
- It usually increases latent load for air conditioning
- It usually humidifies the building in the summer time
- It usually dehumidifies the building in the winter time
True or False - Clogged air filters can cause liquid to flow to the compressor
True
The middle tab one the dial of a conventional fan/limit control is the setting for…
Turning the fan on
True or False - Relays, while they can have numerous poles, can have no more than 2 throws…
True
When installing air conditioning to an old furnace you will need to…(multiple answers)
- Test all safety devices when the installation is complete
- Consider installing an isolation relay
- Check the fan motor HP and consider installing a larger motor and pulley
- Check blower relay and install one if none is present
- Check for 40 VA transformer and install one if none is present
Heat anticipators are… (Muliple Answers)
- Are adjustable
- Are connected in series with the Hg (mercury) bulb
- Are connected in series with a gas valve
The conventional fan/limit combination control…
- Is thermally driven
- Has normally open contacts on the fan side
- Has normally closed contacts on the limit side
- Has a common, removable jumper connecting together the line side of both contacts
True or False - Motors convert electricity to strong, moving, rotating, magnetic, fields…
True
True or False - Fuses are always connected in series to the load
True
Electrons… (multiple answers)
- Create magnetic fields while moving
- Are attracted to protons
- Repel each other
- Are negatively charged
If the interconnecting lineset is greater than the standard length…
Consult the manufacturers installation manual for guidelines
Condensation drain lines (with evap in supply air plenum) must be…
Must be indirectly draining into a trapped drain
The purpose of the crankcase heater is… (multiple answers)
*To keep compressor pressure high when the system is off
* To keep moisture from accumulating in the compressor
* To keep the motor windings active
True or Flase - CFC’s are very stable, one of the only things that can break them down is ultraviolet radiation
True
True or False - CFC’s are very stable, one of the only things that can break them down is infrared radiation
False
True or False - Since HFC refrigerants are so stable, they act as carriers that store chlorine until they they reach the stratosphere where they then release the ozone depleting chlorine
False
Approximatly how much colder is the suction saturation temperature of an air source heat pump than the outdoor air… (heating mode)
It is approximately 20 F colder than outdoor temperature
To recycle refrigerant is to…
Remove it from a system, clean it for reuse by filtering it repeatedly through filter driers
What is the RPM of an 8 inch pulley if the 5 inch drive pulley is spinning at 1360 RPM?
850
Considering the first law of thermodynamics, it is valid to say…
Heat - as a form of energy - cannot be created or destroyed
What would you not find on a typical air source heat pump?
A blower relay
What would you not find on a typical ground source heat pump?
A defrost control
True or False - Because of the heat of compression, condensers must absorb more heat than evaporators.
False
When refrigerant enters the evaporator it should be?
3) Low Pressure, Cold, Saturated, Liquid
When refrigerant enters the metering device it should be?
9) High Pressure, Warm, Subcooled Liquid
When refrigerant enters the condenser it should be?
7) High Pressure, Hot, Highly Superheated, Gas
When refrigerant enters the compressor it should be?
1) Low Pressure, Cold, Slightly Superheated, Gas
Proper setup of a vacuum pump
True or False - Atmospheric pressure has a direct influence on the boiling point of water
True
Proper superheat is an indication that… (multiple answer)
- The evaporator did it’s job
- System charge is correct
Concerning hermetic compressors, when does the compressor draw from the evaporator? (Single cylinder)
Mostly during the suction stroke
A zone damper that fails to open can cause… (heating mode)
Can cause high head pressure for heat pump in heating mode
What should be considered when an evaporator is 65 feet lower than it’s condenser? (multiple answers)
- Metering; because the liquid pressure will be high
- Suction line diameter
- Oil traps in the suction line
If the water flow for an evaporator is higher or warmer than normal what will happen to the compressor amperage…
Compressor amperage will rise
PSC Hermetic compressor motors for residential air conditioning require…
Full equalization of system pressures before they can start
A technician is replacing a faulty compressor contactor. The one that is being removed is a single pole. The one that is being installed is a double pole. How should an off cycle-self regulating crankcase heater be connected to this new 2 pole contactor?
One wire to the line side of one of the poles, and the other wire to the load side of the same pole, then reroute the compressor wire of the opposite pole to it’s line side.
You have just installed an R22 orifice system. It’s running and has a suction pressure of 60 PSIG and a suction line temperature of 70 F and a head pressure of 170 PSIG and a liquid line temperature of 90F. The indoor dry bulb is 76Fand the wet bulb is 70F. The outdoor dry bulb is 82F and the wet bulb is 77F. What is the first thing you should do?
Add more refrigerant
