Key fact that ive learned in charging txv systems and fixed metering. BE PATIENT. .ADD SLOWLY
It's hard to be patient when the sweat is overflowing from your britches because your butt crack can't drain it fast enough.
Originally Posted by zxcb
Guys, this is getting out of control
Charging a system with a receiver to a certain amount of subcooling is 100% wrong.
On a system with a receiver it is MUCH more important to maintain a liquid level in the receiver during all operating conditions. The subcooling value is what it is.
The only way you can manipulate the subcooling to a higher value would be to add enough refrigerant to fill the receiver 100% and overflow into the condenser.
At which point, you have just grossly overcharged the unit.
Since your system has a head pressure control valve.
You want to charge the system to a clear liquid sight glass.
Then add the required calculated additional flooding charge.
It's all about maintaining a liquid level in the receiver during all operating conditions, not subcooling.
If you believe adding refrigerant to a system with a receiver will increase subcooling, then you don't understand why it works for a system without a receiver.
Originally Posted by icemeister
If you have a typical residential A/C system with a TXV, you already know that if you add refrigerant the subcooling will increase...and similarly, if you remove some the subcooling will decrease.
Originally Posted by drife678
But why does this happen? What actually creates subcooling?
Consider what a condenser coil does. It first desuperheats the discharge gas from the compressor, then it condenses that gas to a liquid at saturation and finally it further cools that saturated liquid to a subcooled state.
The key to understanding subcooling here is to realize that subcooling is a simple process of heat transfer from liquid refrigerant to the ambient air. How much subcooling you will get is determined by how much of the condenser coil is filled with liquid refrigerant...ie, more liquid/more subcooling and vice versa. This is called stacking liquid in the condenser.
"OK...So if I add more gas, the subcooling increases because there more liquid stacking up in the condenser coil. What's the difference between that and a what happens in a system with a receiver installed?"
The receiver is connected in the liquid line leaving the condenser coil. It's purpose is to ensure a steady supply of liquid to the TXV as well as to contain excess refrigerant in the system. It allows the condenser coil to freely drain into it, so no stacking of liquid can occur. Any added refrigerant goes into the receiver. No stacking means no increase in subcooling. The amount of subcooling is fixed at whatever the condenser gives you...which is typically around 5°F or so.
If anyone doubts this, please find a system with a receiver, add some refrigerant and watch what happens to the subcooling as you add it.
What level should I maintain the sweat in my buttcrack?
Originally Posted by Phase Loss
Officially, Down for the count
YOU HAVE TO GET OFF YOUR ASS TO GET ON YOUR FEET
I know enough to know, I don't know enough
Liberalism-Ideas so good they mandate them
I like to run mine around 0% during all conditions.
Hey we have all been new and didn't know all the answers at some point. It is tough when your boss throws you the responsibility for something you don't understand. The guy sounds like he knows the basics and is trying to do the right thing. I'm not the most qualified but but I'll try. Plus, being that I'm a maintenance guy, at a hospital, and see truly strange systems, I can relate some.
So yes, depending on what the system is, a clear sight class under some given condition does not equal a properly charged unit under all conditions. You mention a headmaster and a reciever. That means just subcooling isn't enough and you must do the math and calulate your extra chage per instructions. The only possible short cut would be to revisit the system in winter and add freon to get a clear sight glass.
That would assume everything is adjusted right and working as it should be. Based on my experience that is the biggest mistake one can make. You never know what those before you have done in an attempt to make something work and please a boss. So (IMHO) this would be a poor way to approach the situation. You have been given a chance to learn something and advance yourself. Grab the bull by the horns and do the right thing. Everyone feels pressured to tell the boss "I can fix it". I can tell you ...from being the boss to the repair guy....it is better to fess up and say "I don't know but I'm going to do everything in my power to learn why".
Thanks that is what I am trying to do at this point. I will read and calculate the additional charge required and go from there. All this assuming there is not a leak I have not found. Be back out there this moring and snoop around again with the UV light before doing anything else.
Originally Posted by Russ57
Any system with a reciever will use signifigantly more refrigerant. Ive made it a habit to recheck when the box is down to temp.