Subcooling with headmaster

[dorrmann]

What's the proper way to charge a TXV system that runs off of a headmaster? When it's cool outside, I know that the headmaster is in full effect, so a subcooling reading wouldn't provide me with the proper readings.

We usually just do it to a full sightglass, but I know that a lot of the time that results in an overcharge.

Either there isn't any threads on this subject, or the search tool isn't working correctly because I couldn't find anything on it.

[duckman373]

In warm weather, you can charge to a full sightglass. In coldweather,you need to add extra refrigerant after the sightglass clears. Usually seems to be about 2 lbs per h/p.

[270wsm]

In warm weather, you can charge to a full sightglass. In coldweather,you need to add extra refrigerant after the sightglass clears. Usually seems to be about 2 lbs per h/p.

I think you got it backwards. In cold weather you charge to a clear glass and you should be good to go. In warm weather you want to add beyond a clear glass. If you just clear the glass on a warm day, you will be back in the winter adding more refrigerant.

[k-fridge]

The new blends specifically say not to clear it.

Lemme guess.....ICOR.

I give up.......

[engineerdave]

Hmm. We've recently had to recover some of the charge from two different sites. Units ran just fine until ambients exceeded +110*f, then they tripped High Head. Units had been charged to a clear glass during winter season, ambients approximately +60*f. R404a. One LT unit, one MT unit. Same symptoms, same remedy.

[DeltaT]

I read a technical article a few years back concerning why the 400 series refrigerants can't be charged to full sight glasses. It's not that bubble in the sight class mean lack of a liquid columm at the TXV but for some reason the expansion of the tubing at and in the sight glass isself causes bubbling in the 400 series refrigerant.

So the article said something about not being able to use a sight glass in charging procedurers for 400 series refrigerant.

Wish I had kept the article.

[gas_n_go]

I was always under the impression that the rule of not clearing the sightglass pertained to critical charge systems with sightglasses not ones with recievers. I really have not read up on the litature but it dosnt make sense to me how you can say you want a flashing sightglass on a sys that has a reciever. I always charge units by pressure readings, reciever percentage, or by weight if its critical charged.

[dorrmann]

Originally posted by duckman373
In warm weather, you can charge to a full sightglass. In coldweather,you need to add extra refrigerant after the sightglass clears. Usually seems to be about 2 lbs per h/p.

I just took a Copeland teardown class and the rep said that unless the sightglass is at the TXV, clearing it will overcharge it.

The new blends specifically say not to clear it.

[jhd1234]

At http://www.sporlan.com you'll find some literature about charging headmaster systems. Be aware that these systems require oversized receivers to hold the extra refrigerant.

[Dowadudda]

I personally don't buy the theory of the blends and not charging to a full sight glass. In anything I work on, I have a more than ample receiver. If I am clearing the glass, outlet of receiver, and I am under extreme load, I am pretty confident as my TX's close down and that excess gas will stack fine in the receiver and possibly condenser. I have never once not cleared the glass and I have never had any problems with high head, flooding or anything that an overcharge would indicate ever.

In addition to that, TXV's need a full column of liquid to reduce flash off prematurely. Refrigerant is a refrigerant. The arguement is that these blends have this ability to condense and vaporize between two temp points. So what. I still have my super that I need dialed in and I need my full column of liquid for that valve to throttle that gas correctly.

I will give you a great example. You have a 20 ton condensing unit running 404a feeding two coils inside. The condensing units sit at grade, and rise thirty feet and poke in to building. (I did not Build it). That liquid will be subject to extreme pressure drop having to go that vertical route. What happens. pressure drop. What happens when we have pressure drop, we flash, we revaporize right? So the best way to fix this is add a heat exchanger. True. But. If using this theory of not providing a full column of liquid, that gas is still in a somewhat vapor state going up that vertical route. What the hell good is that heat exchanger going to do. We need to be a liquid already and then the heat exchanger further subcools so we don't flash gas. If it's already flash gas were screwed. Don't beleive everything your told..

Your better off getting your liquid correct and adding saftey to your suction side, if you even need to such as an accumilator.

[jeffcolledge]

I had a leak on a walk in freezer during the summer once and wondered the same thing. I was given a chart to follow which outlined each refrigerant, evap. coil temp desired and the required "extra" weight to be added for the ambient temp. I thought "great idea"...It was way off!! Basically what ended up happening was the customer called on the coldest day of the year complaining that his freezer would not drop below 30F. I checked, and found that the head master was doing all that it could, there just wasn't enough ref. to stack the condenser. Unless there is a fool-proof way of doing it in warmer ambient temps, I think you have to go back when it's cold.

[icemeister]

One sure way to charge a system with a Headmaster in warm weather is to determine the pumpdown capacity of the system receiver (typically 80% of full) and weigh in your charge to that amount. If the system is on a pumpdown control you simply can't add more than that........and it may save you from a callback on a very cold day.

Of course if you're charging one of those blends and you clear the SG you'll go blind I've heard.

(Or was it hair on the palm of your hand?)

[wannafreeze]

One sure way to charge a system with a Headmaster in warm weather is to determine the pumpdown capacity of the system receiver (typically 80% of full) and weigh in your charge to that amount. If the system is on a pumpdown control you simply can't add more than that........and it may save you from a callback on a very cold day.

Of course if you're charging one of those blends and you clear the SG you'll go blind I've heard.

(Or was it hair on the palm of your hand?)

Now I know what I could use the pump down capacity for.Do you think I could determine the amount of refrigerant in the receiver without recovering the refrigerant?I remember Markettech mentioning a torch method on a system while it's running..Torching the receiver from bottom upwards then feeling the temperature change point to determine how full the receiver is...