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Good to see you got it and I would leave that charge right where it is for K,C.

Originally Posted by tomnkc

-20 would be at the bottom of the of the scale for here in the KC area. But cosidering windchill it is a possibility. Also I misspoke/miswrote in my last post. Meant to say I have 6-9degrees of superheat not subcooling. Sorry about that. Still not sure if the temps are accurate based on what I posted before

Windchill doesn't affect refrigeration equipment.

Originally Posted by 2sac

No. Lineset probably being the biggest variable. With extended lineset runs adding a winter charge and subtracting a summer charge may be necessary unless you add an additional receiver. Refrigeration Research can give you an idea about how much refrigerant the receiver holds. Is -20 a probability in your neck of the woods?

-20 would be at the bottom of the of the scale for here in the KC area. But cosidering windchill it is a possibility. Also I misspoke/miswrote in my last post. Meant to say I have 6-9degrees of superheat not subcooling. Sorry about that. Still not sure if the temps are accurate based on what I posted before

You misseded a step.....

Once you arrived at the 5.4# figure, you need to take that number to Table 2.

So, assuming (bad idea, I know) a -25F evaporator and a -20F minimum ambient, you need 88% of that 5.4# figure or 4.752#.

Since you've already put 4# in past a clear glass, add 12 ounces and call it DONE!

Originally Posted by tomnkc

when I began to explain the charging procedure to him I could see the lights go out and he just said "do whatever you think is right"!!!

that's good!

Originally Posted by tomnkc

Is there a way to tell if a system is indeed charged for all ambient temps without dumping the charge and starting from scratch?

No. Lineset probably being the biggest variable. With extended lineset runs adding a winter charge and subtracting a summer charge may be necessary unless you add an additional receiver. Refrigeration Research can give you an idea about how much refrigerant the receiver holds. Is -20 a probability in your neck of the woods?

[QUOTE=Tommy knocker;13917851]You've got alot of good info on this thread now go kill it and drag it home.[/QUOTE


I did just that! Sorry for the delay in an update but the last week has been busy. The 100 degree + Month of July sure weeded out the weak ones.

My walk-in is up and running and has been for a week. I am notb entirely sure I have a complete full charge yet that will operate system @ -20 ambient. but it is working well in the 65-100 degree ambient we have been experiencing the last 10 days. I still do have a couple of questions though.

On determining a full charge to (-20) ambient this is the way I figured it based on the the Sporlan bulletin 90-30-1.
Condeser is 3/8" tubing, 28" long with a total of 42 tubes and 42 return bends.

42x28=1176/12=98lf of tubing 42x.200=8.4lf for the return elbows Total tubing =107lf

107x .050= 5.4 lbs additional refrigerant after inital fill to clear sight glass.

My initial charge was 6lbs 4 oz to clear sight glass. I added and additional 4 lbs beyond that. In my mind 5.4 lbs additional seemed like alot for the small system that this is. That would put the total charge at aprox 12lbs. Right now it has 10.5 lbs. I understand the problem may come as Winter gets here and the ambient drops. Did I figure the additional charge properly?

Is there a way to tell if a system is indeed charged for all ambient temps without dumping the charge and starting from scratch?

Next, Sub cool as I measure it is somewhere between 6 and 9 degrees. From what I read suction temp and pressure should be measured at the TXV bulb. Temp is not a problem but this system has no service valve at the evaporator. Service valve on suction line is located on condenser which is just outside the cooler with about 8' of insulated line in between.How accurate is my subcool temp? Seems to me you might have a slight rise in suction temp/pressure between the evap and the service valve.

Thanks again to all who have helped. I found out this week that I might just have a little more knowledge about this system than my boss who had this job before me. Great guy but when I began to explain the charging procedure to him I could see the lights go out and he just said "do whatever you think is right"!!!

You've got alot of good info on this thread now go kill it and drag it home.

Any system with a reciever will use signifigantly more refrigerant. Ive made it a habit to recheck when the box is down to temp.

Originally Posted by Russ57

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.

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".

I like to run mine around 0% during all conditions.

Originally Posted by Phase Loss

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.

What level should I maintain the sweat in my buttcrack?

Originally Posted by icemeister

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 drife678

Confused

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.

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.

Confused

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.

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.

http://www.sporlanonline.com/90-30-1.pdf

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.

Originally Posted by zxcb

It's hard to be patient when the sweat is overflowing from your britches because your butt crack can't drain it fast enough.

Amen!!

It's hard to be patient when the sweat is overflowing from your britches because your butt crack can't drain it fast enough.