HVAC Final Flashcards
What temp range is used for soldering versus brazing?
Soldering: under 800, usually 361 to 500. Brazing: over 800 to 1500
What causes solder to flow into the joint?
Capillary Attraction
What tools are used for soldering?
Propane or butane torch, flux, solder, appropriate solder tip
What tools are used for brazing?
Air-acetylene, regulator, hose, and torch with appropriate tip, silver solder, flux for high silver content
When soldering, where should flux be applied to?
The male end only
95/5 solder should be used
on the low side of the system, too low of a melting point. Also used for water pipes
When cleaning ACR copper tubing before soldering, a material that can be used is
Sand Cloth
Before using a voltmeter, always
Set the range selector to a setting higher than the voltage you expect to read
A gauge and manifold assembly used in refrigeration work may include
2 or 4 way valves, compound or standard gauge, manifold, valves and hoses, a 4 way valve design using a shutoff valve for each hose
A Sling Psychrometer measures what?
Dry-bulb and wet-bulb temps of air
T or F, An Electronic Charging Scale measures the volume of refrigerant flow into a refrig system.
F, measures by weight
How is ACR tubing measured?
OD
How is plumbing piping measured?
ID, Nominal
What are copper pipe gauge sizes, in order of thickness?
ACR, K, L, M, DWV
What side of a HVAC system piping should be insulated?
Suction Side to prevent heat absorbtion, excessive superheat
What is the silver percentage range for brazing solder?
15-60 percent
For brazing with Air-acetylene, where is the red hose connected and where is the green hose connected?
Red for B-Tank, Green to oxygen regulator
Why is Nitrogen pumped into pipes for brazing?
To force air out to reduce oxydation
What factors affect Evaporator capacity, efficiency?
Overcharge (low or no superheat), undercharge (high superheat), dirty coils, fan speed or water flow, expansion valve starving coil, recycled air, blocked air flow
What is the highest the water coil should be compared to the evap refrig (Approach)?
10 Delta T. Smaller approach, more efficient
What is the job of the Condenser?
De-superheat, shed heat, subcool (5-20 degrees)
What factors affect Condenser capacity, efficiency?
Recirculated air or water, fan speed or water flow, undercharge, overcharge, too high superheat
What causes high or low superheat?
Undercharge, overcharge. Added resistance to heat exchange surface.
How do you calculate the correct head pressure?
Condenser ambient temp + unit’s designed condense temp = Condensing temp
What causes ice build up?
Low charge, failing metering device
What is a Direct Expansion Evaporator?
Dry-type evap, meaning they establish superheat at the evap outlet. Normally use TXV. Used for smaller chillers up to 100 tons for modern chillers.
What are the symptoms of an overcharged system?
High discharge pressure, and maybe high suction pressure, liquid slugging into compressor. Low super heat. AXV won’t have high suction pressure, due to mainaining constant pressure. TXV might.
How does a TXV meter refrig?
Using a sensing bulb to monitor superheat
How does an AXV work?
In reverse to TXV, works by suction pressure closing the valve during high load and opening during low load to maintain suction pressure.
What are the box operating temps for low, med, high refrig?
0 and below, 35 to 45, 70
