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Old 11-01-2008, 10:49 AM   #1
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Pre-charge on goodman straight cool


GSC14 4 ton.
4-5 Goodman multi position multi speed

I'm running 15ft of 3/8 and 7/8 line set. The unit comes precharged for 15 ft of line set. Does that precharge take the volume of the evap coil into account as well?

I feel pretty comfortable with brazing the line set under N2 and pumping it down before opening the precharge. It's when you start talking about adding or removing R-22 that scares me away.

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Old 11-01-2008, 11:50 AM   #2
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Pre-charge on goodman straight cool


You will have to measure the superheat if the coil is a fixed orifice to determine the refrig volume.

If the coil comes with a TXV you must use the sub-cooling chart to determine refrig volume.

This reading will only be valid with with the correct cfm airflow.

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Old 11-01-2008, 11:55 AM   #3
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So I can't just run 15', vac out moisture and open the charge in the condenser? The condenser says it's precharged with r-22 and oil for 15 of line set. It's an orifice type. No TXV.

Last edited by protechplumbing; 11-01-2008 at 12:04 PM. Reason: spelling, typos
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Old 11-01-2008, 12:15 PM   #4
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Pre-charge on goodman straight cool


Most pre-charges are set for the length of the line-set (15 ft in this case) and the coil of matching tonnage, but superheat/cool test should be done after installation anyways.
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Old 11-01-2008, 12:22 PM   #5
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Pre-charge on goodman straight cool


Let me clarify. I'm doing a "cut in". There wasn't any central air before. I'm cutting in registers, Running flex w/ duct board plenums, Air handler is going in the attic thru a gable cut. Condenser is going on the ground below the gable cut. I understand the basics of the vapor compression refrigerant cycle but I don't have a recovery machine. I do have gauges and a vac pump. silfos and oxy/acetylene. I have to go pick up a nitro bottle and reg. (I need one anyway for leak detection in plumbing)
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Old 11-01-2008, 12:23 PM   #6
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Cool. Will do. Many thanks.

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Originally Posted by SD515 View Post
Most pre-charges are set for the length of the line-set (15 ft in this case) and the coil of matching tonnage, but superheat/cool test should be done after installation anyways.
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Old 11-01-2008, 01:14 PM   #7
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Pre-charge on goodman straight cool


Ok I see where you are coming from now.


As an HVAC techs we did not "assume" the right amount of refrig is going to be in the system. (especially from Goodman) from the factory.

We confirm the volume of refrig by performing the superheat or sub-cooling test.

Make sure the AHU is not blowing more CFM than the nominal tonnage of the AC. That will give you false reading.
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Old 11-07-2008, 04:49 PM   #8
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I ended up using close to 20 feet of line set. Did super heat test. Its 7 deg above goodman's number. About how much r-22 would be needed?
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Old 11-08-2008, 12:45 AM   #9
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Pre-charge on goodman straight cool


Add small amounts and wait half an hour before before rechecking SH.
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Old 11-08-2008, 06:23 AM   #10
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Quote:
Originally Posted by protechplumbing View Post
I ended up using close to 20 feet of line set. Did super heat test. Its 7 deg above goodman's number. About how much r-22 would be needed?
There is no one set amount that will lower the Superheat by X degreees.

The install directions however. Should have contained a section that told you how much charge to add per additional foot of line set and for the coil match you used. If it was an approved coil match.
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Old 11-09-2008, 04:28 PM   #11
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I got the charge right. Now for the ducts. I'm planning on running quiet flex. see pics. If you think this design will fail catastrophically let me know as I'm making this up as I go.
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Old 11-09-2008, 04:39 PM   #12
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Bwahhahahahahahahahahahahahahahah!

Think of that as a plumbing lay out and then ask that question.
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Old 11-09-2008, 07:57 PM   #13
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I was hoping for help rather than laughs.

My line of thinking was a "flow balanced manifold"

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Old 11-09-2008, 08:26 PM   #14
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Quote:
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I was hoping for help rather than laughs.

My line of thinking was a "flow balanced manifold"

Just ribbing 'ya.

To me it does not look exactly right. We got some guys, one named Beenthere, who can guide you thru this. Flex duct is unforgiving and I have to confess I am more a sheet metal guy myself. I am just worried that with all the takeoffs from diff trunks may not give you good airflow.
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Old 11-09-2008, 11:40 PM   #15
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Pre-charge on goodman straight cool


First.
How can you have the charge right without the duct work hooked?
Second.
16" round sheet metal is too small for 4 tons, let alone 16" flex duct.

Do you plan on using tee's, wye's, or what method for tapping in your supply branches to your trunk line.
Same question on return.


PS:
Also, you only show 10-6" supplies. Thats a lot of air to try and move through a 6' round duct.
Your going to get air noise.

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Last edited by beenthere; 11-10-2008 at 12:16 AM. Reason: Added PS:
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