Week 4 Random HW A
Why are systems with fixed restriction metering devices critical to charge?
They cannot adjust to changing conditions and they have no liquid receiver to store extra refrigerant.
In a refrigeration system, why are expansion devices located closer to the evaporator?
To minimise the heat gain.
What does TW(Tare Wright) on a recovery tank mean?
Weight of the tank empty/no refrigerant.
Recovery of a system means what?
Removing refrigerant and storing in a certified recovery tank.
How does an LED refrigerant leak detector work?
By reflecting off the dye infused oil with a UV light to show the pressence of a leak.
Why should a system be leak tested after it has been repaired before it is charged?
Systems with leaks cannot be properly evacuated; air will just suck in through the leak. Recovering refrigerant after it has been added adds to the time required.
How often should the refrigeration oil in a compressor be changed?
Refrigeration oil does not need regular changing. Refrigeration oil is usually only changed to clean up a contaminated system or to add a retrofit refrigerant.
“Full recovery” of a system is also known as this.
Evacuation
WC on a recovery tank stands for what?
Water capacity. Capacity of liquid refrigerant.
How do leaking systems cost their owners money?
Use more electricity, lower effeciency. Cost of repair and replacement of refrigerant.
How does an overcharge affect the superheat of a fixed restriction system?
An overcharge will decrease system superheat.
How does an undercharge affect the superheat of a fixed restriction system?
An undercharge will increase system superheat.
Recover refrigerant from a leaking system until the pressure in the system is...
0 PSI
If a system will not hold a vacuum after it has been evacuated what should the technician do?
Find and repair all leaks and retest to see if vacuum holds.
How do soap bubble solutions indicate very small refrigerant leaks?
Tiny leak will form a white froth of micro-bubbles with escaping nitrogen or refrigerant.
What is the best method to charging a small appliance that holds less than a pound of refrigerant?
Vapor with the system not operating up to a specified static pressure at a specified ambient temperature.
Give an example of a condition that can make a system appear overcharged even though the charge is correct.
Low airflow over the condenser or non-condensable gasses
Why does the the nitrogen regulator do?
Lowers the pressure leaving the nitrogen tank to safe level for testing the system for leaks.
What do you do with the nitrogen that is in the system after pressure testing?
Vent it! The are is mainly nitrogen and it is safe to vent it.
Why should technicians never use oxygen to pressurize refrigeration systems when leak testing?
MIxtures of refrigerant oil and oxygen can be explosive.
What happens to the refrigerant going through the metering device?
The refrigerant's pressure drops dramatically, causing a small amount of the liquid to flash to vapor, which causes a dramatic temperature drop.
How often should the vacuum pump oil be changed?
Most vacuum pump manufacturers recommend replacing the oil in the pump after each evacuation.
What is the preferred gas to use to pressure test an ac system for leaks?
Nitrogen
A recovery tank should not be filled with liquid refrigerant above this amount of the Water Capacity (WC).
80%
What leak-detection method does the EPA consider the best for pinpointing leaks?
Soap Bubbles