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Old 05-18-2011, 09:12 PM   #16
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Checking charge using Subcooling


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Originally Posted by Doc Holliday View Post
I hear furnace and a/c but does the evaporator coil have a txv or a fixed orifice metering device such as the normal piston? If piston (or old school cap tube) then charge superheat, not subcool.

And make damn skippy both your inside and outside coils, evaporator and condenser coils, are clean and that your static pressures are correct or there is no reason in checking your charge in the first place.

Industry standard and manufacture design, if you want it done right.
Yes, this has a Bryant cased coil with a built-in TXV, so that's why I was asking about SC. To your second point, the condenser and coil were new when installed last fall, so they are both still very clean and the static at 1100 cfm with the furnace running is 0.56, so that should be fine.

So, back to my original question, the guy I hired casually added some R410a to account for the increased lineset length of 10-feet. If he overshot by, say, 10-oz and put in a full pound, would the SC be off by more than one or two degrees? BTW, the rating plate calls for an SC of 13-deg F.

As an aside, how does the manufacturer know the capacity of the evaporator you plan to match with your condenser? If I installed a matched, but oversized evaporator (3.5-ton coil with a 2.5 condenser), would that also require additional charge to be "full"?

Thanks.

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Old 05-18-2011, 09:32 PM   #17
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Checking charge using Subcooling


[quote=beenthere;650536]You install or work on a few "high" SEER units. You get use to seeing large amounts of factory charge.

If you don't work on a lot of "high" SEER, it sounds like too much of a charge.[/quote

You are right Been, my bad. we can't even give away 16 seer in this neighborhood (Tax credit or no. We are just now getting a few call back to work at some of our auto related industries) and I have yet to install one so I have some catching up to do.
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Old 05-18-2011, 09:36 PM   #18
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Checking charge using Subcooling


Quote:
Originally Posted by civiltoatee View Post
Yes, this has a Bryant cased coil with a built-in TXV, so that's why I was asking about SC. To your second point, the condenser and coil were new when installed last fall, so they are both still very clean and the static at 1100 cfm with the furnace running is 0.56, so that should be fine.

So, back to my original question, the guy I hired casually added some R410a to account for the increased lineset length of 10-feet. If he overshot by, say, 10-oz and put in a full pound, would the SC be off by more than one or two degrees? BTW, the rating plate calls for an SC of 13-deg F.

As an aside, how does the manufacturer know the capacity of the evaporator you plan to match with your condenser? If I installed a matched, but oversized evaporator (3.5-ton coil with a 2.5 condenser), would that also require additional charge to be "full"?

Thanks.
Can't speak for Bryant but ICP and Nordyne both say +/- 2 or 3*f degrees.

I would probably think it would be the same for your equip.
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Old 05-18-2011, 09:45 PM   #19
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Checking charge using Subcooling


Forget the length of the line set. Superheat and subcooling go hand in hand, txv or not. There are considerations such as ambient temperatures and wet bulb temps which equate to formulas to derive a system's proper target charge so again, forget your lineset length. That is over and yesterday and not important any longer. Proper cfm is as well as those other considerations so with your slightly higher than average static pressure I'm going to assume you are close to nominal as you are going to allow your system to be. I should ask where were the measurments taken to come up with .56" anyways but I won't.

Anywho, here's some good info you can read and study. All systems pretty much act the same, the same rules apply. Good luck!!

http://www.udarrell.com/ac-trouble-s...ubcooling.html

http://www.hvacsalesandsupply.com/Li...20Charging.pdf
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Old 05-19-2011, 05:47 AM   #20
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Checking charge using Subcooling


Carrier recommends 350 cfm/ton from a chart I saw on a newer MXA high efficiency unit. You may want to be around 900-1000 cfm for better performance with their units. Probably best to get a Carrier/Bryant tech from a large well established company to check it. Ask for the senior tech and hope he knows his stuff. If it is a Carrier furnace that info should be with the setting fan dip switches section in the install manual AND on the sticker on the door with the wiring diagram if you have an ECM motor.
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Last edited by yuri; 05-19-2011 at 06:00 AM.
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Old 05-19-2011, 08:08 AM   #21
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Checking charge using Subcooling


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Carrier recommends 350 cfm/ton from a chart I saw on a newer MXA high efficiency unit. You may want to be around 900-1000 cfm for better performance with their units. Probably best to get a Carrier/Bryant tech from a large well established company to check it. Ask for the senior tech and hope he knows his stuff. If it is a Carrier furnace that info should be with the setting fan dip switches section in the install manual AND on the sticker on the door with the wiring diagram if you have an ECM motor.
You are correct, Yuri. For the first time, last night, I checked with the A/C running and the CFM is 875 and has a current static of 0.41". I have an Evolution furnace and control, so the control sets the CFM automatically for the condenser size it connects with. The static I reported earlier (0.56") was with the furnace running on high stage at somewhere around 1100 CFM. I had anticipated that the CFM for the A/C would be the same or higher, but in my case, living in MN, I need a larger furnace and smaller A/C, so the CFM and corresponding static for A/C is a bit lower than the high stage in heating mode.

BTW, all of the CFM and static readings I have been reporting are displayed directly by the Evolution stat and are somehow derived from the rpm and load on the ECM motor. It is my understanding that they are fairly accurate.

So, Yuri, are you suggesting that increasing the CFM above the 875 automatically set by the stat might provide better performance?
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Old 05-19-2011, 09:35 AM   #22
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Checking charge using Subcooling


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BTW, all of the CFM and static readings I have been reporting are displayed directly by the Evolution stat and are somehow derived from the rpm and load on the ECM motor.

That is so dang cool.
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Old 05-19-2011, 04:07 PM   #23
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Checking charge using Subcooling


LOL i must be serving the poor segment of the market. Went to a training seminar on the Evolution but have yet to see one.
I am at Uncle Clover"s house right now doing some stuff.
Uncle Clover is not walking well at all.

He's turned into a bear and biting every bodies head off.

I'm keeping him away from the computer.
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Old 05-19-2011, 04:16 PM   #24
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Checking charge using Subcooling


Quote:
Originally Posted by civiltoatee View Post
Yes, this has a Bryant cased coil with a built-in TXV, so that's why I was asking about SC. To your second point, the condenser and coil were new when installed last fall, so they are both still very clean and the static at 1100 cfm with the furnace running is 0.56, so that should be fine.

So, back to my original question, the guy I hired casually added some R410a to account for the increased lineset length of 10-feet. If he overshot by, say, 10-oz and put in a full pound, would the SC be off by more than one or two degrees? BTW, the rating plate calls for an SC of 13-deg F.

As an aside, how does the manufacturer know the capacity of the evaporator you plan to match with your condenser? If I installed a matched, but oversized evaporator (3.5-ton coil with a 2.5 condenser), would that also require additional charge to be "full"?

Thanks.
The manufacturer test and rate their unit with their coils that are matches. And also list additional charge amounts for those coils that need additional.
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Old 05-19-2011, 04:20 PM   #25
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Checking charge using Subcooling


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Originally Posted by hvac5646 View Post
LOL i must be serving the poor segment of the market. Went to a training seminar on the Evolution but have yet to see one.
I am at Uncle Clover"s house right now doing some stuff.
Uncle Clover is not walking well at all.

He's turned into a bear and biting every bodies head off.

I'm keeping him away from the computer.
Tell him I said hi. And wishing him a speedy recovery.
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Old 05-19-2011, 04:20 PM   #26
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Checking charge using Subcooling


At 875 CFM, sounds like you may have the controller set to comfort. Economy will increase the CFM. But your humidity could rise.
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Old 05-19-2011, 05:24 PM   #27
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Checking charge using Subcooling


I agree with Beenthere, let it set the cfm itself. The figures I quoted are for manually setting the dip switches on a basic high eff unit w/o evolution control but with an ECM motor. Yours does it for you.
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Old 05-19-2011, 06:54 PM   #28
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Checking charge using Subcooling


Quote:
Originally Posted by hvac5646 View Post
LOL i must be serving the poor segment of the market. Went to a training seminar on the Evolution but have yet to see one.
I am at Uncle Clover"s house right now doing some stuff.
Uncle Clover is not walking well at all.

He's turned into a bear and biting every bodies head off.

I'm keeping him away from the computer.
Feed him some blue berries and maybe he will sweeten up. I hear bears like berries. Tell him Yuri the Russian bear says Hi.
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Old 05-19-2011, 11:19 PM   #29
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Checking charge using Subcooling


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Feed him some blue berries and maybe he will sweeten up. I hear bears like berries. Tell him Yuri the Russian bear says Hi.
Strong family resemblance...especially the Greek nose.

I am tempted to double his pain meds to mellow him out.

Staying steady. Uncle has a lot of friendly, dedicated customers customers.

Sorry if I took over the thread..but Uncle was smacking me in back of my head to post something here.
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Old 05-20-2011, 10:51 AM   #30
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Checking charge using Subcooling


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Originally Posted by beenthere View Post
At 875 CFM, sounds like you may have the controller set to comfort. Economy will increase the CFM. But your humidity could rise.
Thanks, Been,

I have not monkeyed with the comfort/economy setting. I will check, but it does sound right that 875 would be comfort and economy would be higher. We generally don't use the A/C until the temp is above 85, so it may not matter in our case.

I do know that I installed a 3.5-ton (or was it 4.0-ton) ARI match, cased coil to get the 16-seer rating needed for the government tax credit. It is my understanding that the system will be more "efficient" with the oversized coil, but will likely not do as good of a job at removing humidity. Therefore, I am probably better off run in the lower CFM, comfort mode to offset the oversized coil.

BTW, I checked the product data literature for my coil:

http://www.docs.hvacpartners.com/idc...t/cnpv-7pd.pdf

but it does not appear to indicate the additional charge that might be required when going from a "truly" matched 2.5-ton coil CNPVP3021ATA to an oversized, but ARI matched, 16-seer (3.5-ton) coil CNPVP4221ATA. Do you know where that info would be found?

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