ReplyOriginally Posted by EricDMKAJ
http://sporlanonline.com/literature/90/90-30-1.pdf
Print it, laminate it, read it twice and keep it in your van to reference.
This is the best method that I've found for charging headmaster and ORI/ORD type systems.
Regular Guest
Hello!
I am currently in the process of switching jobs doing Res HVAC/R to doing light commercial. Mainly Walkin Coolers, Freezers, Ice machines. All the work will be done in gas stations. The company thats hiring me knows my experience level is residential, and are willing to train me in the light commercial side of things. Now, since central AC is so easy, i feel i've been spoiled after going through my old school books while brushing up on my knowledge. Certain things are making my head spin, and was wondering if i could get some input.
-Head Master Controls are confusing me big time. To my understanding, when charging a Head Master control system, if you charge in the summer time by filling the sight glass, you'll be able to hit your desired head pressure (ambient+30, converted to pressure), and low side (20 degrees colder than box temp) relatively easy. looking for 6-8 super heat on cooler, 4-6 super heat on freezer. However, once the cold weather comes, and the head master control kicks in, my charge won't be right anymore. Now, ive heard various theories on how to charge properly. One way i heard was charge to sight glass in summer, and add 2 lbs per h/p. Another is full sight in summer, plus 20% of capacity.
Now, those charging methods are done by adding to exising refrigerant. For example, leak in evaporator. Pump down into receiver, change evap, pull vaccum, and then add to sight glass till clear and either add 2 lbs per h/p or 20% of capacity. Is any of this true? Is it possible to add to existing refrigerant with head master, or do you have to evacuate system and then weight it all in?
Also, while charging Residential Central Air, charging is done by sub cooling if unit has TXV, super heat if unit has fixed orrifice. Checking superheat back at compressor and sub cooling at outlet of compressor, while checking humidity with psychrometer and outside temp. Is this still true with package AC and light commercial split AC systems?
Thank you!!
Professional Member
http://sporlanonline.com/literature/90/90-30-1.pdf
Print it, laminate it, read it twice and keep it in your van to reference.
This is the best method that I've found for charging headmaster and ORI/ORD type systems.
Regular Guest
Nice!
Stupid question, but is charging by that method done by evacuating the system and weighing it in? Or can you start charging based on that with refrigerant already present in the system
(Edit) Oops, after reading it further, i see that it doesnt matter. it can be charged evacuated or with exising refrigerant
Also, while charging Residential Central Air, charging is done by sub cooling if unit has TXV, super heat if unit has fixed orrifice. Checking superheat back at compressor and sub cooling at outlet of compressor, while checking humidity with psychrometer and outside temp. Is this still true with package AC and light commercial split AC systems?
Professional Member
I'll *assume* that this is based on a refrigeration unit with a receiver, a headmaster and a sightglass.
The charging method BEGINS with "Charge to clear the sightglass" Given that, you can start at any state of charge and properly charge the equipment.
Read the document that I posted. Seriously.
Professional Member
http://sporlanonline.com/literature-...lating-valves/
Some more good reading here.
For better understanding of headmaster and ORI/ORD type valves, focus on the 90-30 documents.
Regular Guest
Wow, i can't believe i've never seen this information before. thank you thank you! And as far as the packaged AC, and split system AC, that is charged the same way as done in a residential setting i assume. gather ambient temperature, wet bulb, and follow chart just like you would normally, correct?
Professional Member*
Yep
Regular Guest
Thank you! This site is amazing. I know ill need a refresher on oil furnaces eventually, so this will definetely come in handy haha
Professional Member
Yep.
Just noticed that you're fairly close to me. I work the greater Y-town area into PA and WV
Regular Guest
Wow, small world. Poor Youngstown has gotten do depressed, hoping it turns around eventually. Another question....as far as fan cycle controls, im assuming to charge these properly, you have to keep the condenser fans running to know your high side (ambient + 30, converted to pressure). how would those be charged in the winter/summer? do you have to add the additonal winter charge for those like you would for a head master? i dont believe i would have to, im assuming i could charge it the same year round
Professional Member
Most units that I see have a means of head pressure control like a Headmaster or ORI/ORD valving setup.
Make sure the condenser fan is running, charge per the 90-30-1 that I posted and you will be fine.
If if DOESN'T have a low ambient control valve, you're stuck on "best guess" charging methods.
What I'll typically do is just follow the chart anyway. It has worked for me so far.
The "ambient +30 doesn't always hold true, BTW. It's a fair "guess" particularly at high ambients but it is really only a guess. Once your ambient drops, that number flies off the roof.
Regular Guest
I understand everything you're saying, I just have one issue. The only way to charge by sporlans way is to first evacuate the system. Then, weigh in charge to sight glass. Then, depending on how much you weighed in (changing based on ambient), you take difference of that and what is supposed to be in condensing unit. So, just to be clear, there is no way to charge these correctly without first evacuating entire system? Sorry to be a pain...
Regular Guest
You know, I've read this sporland document all day, and it finally clicked. You have to evacuate system completely of refrigerant before starting this process. Then, you figure out the volume of condenser. Then, you weigh in refrigerant until glass clears. You subract the number you just added from your total, and that's the additional you have to add in. Correct? Thank you so much, I am a tech that fully believes in the science side of the trade, and hate charging based on WAG. Thank you. You're a life saver
Regular Guest
And, one other thing that you said. Just to make sure I understood you correctly. On fan cycle control units, you still charge using the 90-30-1 chart?
Professional Member*
You do not have to remove all the refrigerant to charge to the sporlan chart. Clear the sight glass first. Then add the refrigerant per the caculations from the chart to add refrigerant needed to operate in lowest expected ambiant.
Professional Member
Keep reading, Eric.
Let me try to sum it up for you.
Let's assume an 80 degree ambient (for simplicity sake)
Come up on a unit that is low on charge. Sightglass flashing hard.
So, we find and fix the leak and start adding gas.
Step one is to clear the sightglass. It doesn't matter how much or how little gas is in the unit to do this. Just add enough to clear the glass.
Now, run Sporlan's numbers and reach your computed flooding charge and weight that charge into the unit.
You're done.
It gets more complicated charging them on a colder day, but let's get you straight on this, first.
Professional Member
Most fan cycle units that I work on also have a headmaster.
On those very few that don't, I'll add the computed flooding charge and go, too.
Regular Guest
Excellent. Ok, now I see what you're saying. Sorry for all the confusion, I'm just so used to refrigerators (critical charge) and central air, which I just charge by sub cool for Txv, and superheat for fixed orifice.
So, as far as charging on a cold day, how is that done differently?
As far as the lowest possible ambient, should I assume based on the area that I work, or is that stated on the condensing unit.
And lastly, I was taught that if a unit has a receiver, I can't check sub cooling. And if it has an accumulator, I can't check total superheat at the compressor. True? Or not true.
Thank you so very much for helping me through this. Going to the new job, they know my knowledge level is residential, and are training me accordingly. I just want to be prepared with the basics before I get knees deep in it
Professional Member
How is it charged differently? READ the document. It is rather difficult to explain, but the authors at Sporlan did a good job.
Basically, you calculate the total flooding charge for a warm day, THEN calculate how much the condenser is ALREADY flooded due to the lower ambient, then add the difference.
The minimum ambient is for the area that you work. I use -20 around here because, well, it happens every few years.
You CAN check subcooling on a receiver system, it just isn't a good charging metric. Just as you CAN check superheat on a system with an accumulator.
No problem on the assist. We all have to start learning somewhere.
Regular Guest
Excellent. Ok, I'm going to try to soak this document in as much as possible. I'll get it to stick, haha. Thanks again.
Going back to the accumulator, your evap superheat shouldn't change, but total superheat should, is how I understand it. I would assume accumulators used on cap tube or orifice split AC?
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