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Old 02-19-2012, 01:01 PM   #1
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Calculating charge on Goodman SSZ14


Hi,

I have a 2.5 Ton Goodman SSZ14 heat pump SSZ140301A.

I'd like to calcuate the charge using the subcooling method in heating mode since it is Feburary..


I belive these are the steps:
  1. Hook up the Hi pressure gauge to the small liquid line port
  2. Hook up the lo pressure gauge to the service port above the port valves (this goes right into the compressor on a HP)
  3. Run the sytem for 10 minutes or so without defrost cycle
  4. Verify the pressures meet the chart for given indoor dry bulb and outdoor ambient and nominal CFM.
  5. measure the temperature of the liquid line leaving the indoor coil
  6. measure the high pressure of the liquid line at the port valve.
  7. Take the pressure reading of the liquid line and convert it to the saturating condesing temperature via a R410a PV chart.
  8. Take that temperature and subtract the temperature from the indoor liquid line temperature. This is the subcooling temperature.
  9. Compare this to the manufactur ratings.
OK, now my questions.

1. Does this procedure look right?
2. Where do I find the subcool ratings IN HEATING MODE for this heatpump? (it is 9F +-3F in cooling mode)
3. I have a variable speed furnace that has a settable CFM, but what if my CFM is too hi or too low, how does that affect the readings?
4. Which is more likley to wear out the compressor, too much charge or too little?
5. My heating tables don't include my indoor coil. I have a 3636 but the table only pairs a 3642 coil (which is a little bigger). Do they publish more tables somwhere other than the datasheet, how should I addjust with a larger coil than listed in the tables?

Thanks!

-Jeff

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Old 02-19-2012, 02:49 PM   #2
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Calculating charge on Goodman SSZ14


Quote:
Originally Posted by zootjeff View Post
OK, now my questions.

1. Does this procedure look right?
No.

2. Where do I find the subcool ratings IN HEATING MODE for this heatpump? (it is 9F +-3F in cooling mode)
There are no SC listings for heating mode.

3. I have a variable speed furnace that has a settable CFM, but what if my CFM is too hi or too low, how does that affect the readings?
Yes that would effect the readings.

4. Which is more likley to wear out the compressor, too much charge or too little?
About the same wear out time either way.

5. My heating tables don't include my indoor coil. I have a 3636 but the table only pairs a 3642 coil (which is a little bigger). Do they publish more tables somwhere other than the datasheet, how should I addjust with a larger coil than listed in the tables?

Thanks!

-Jeff
Charge should be weighed in, and then rechecked in spring when its warm enough outside to check in cooling mode.

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Old 02-20-2012, 09:37 AM   #3
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Calculating charge on Goodman SSZ14


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Originally Posted by beenthere View Post
Charge should be weighed in, and then rechecked in spring when its warm enough outside to check in cooling mode.

Is this guy full of it then?


http://hvacreducationtechtips.blogsp...t-pump-in.html
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Old 02-20-2012, 12:00 PM   #4
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Calculating charge on Goodman SSZ14


So I have another question if I'm not suppose to check my heatpump charge in the winter..

If the correct way to verify this in the winter is to weigh it in. How do you figure out how much to weigh in?

From what I can tell, neither the Technical Service Manual ,Technical Specification Manual, or Specifications Manual include the proper way to determine the charge due to differences in coils.

The 2.5ton SSZ14 heat pump says:

195 oz factory charge. Includes 15 ft of line-set. Add 0.6oz per foot of additional liquid line.

The manual also suggests that you can use the 3642, 3743, 3636 coils.

Which coil did they spec the charge with?

Doesn't a 3636 use less refrigerant than a 3642 coil?
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Old 02-20-2012, 02:50 PM   #5
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Calculating charge on Goodman SSZ14


The charge is speced for all those coils. You just have to add.6 oz per foot over 15 foot.

Beenthere is saying to weigh in the charge in winter and fine tune in summer for cooling.
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Old 02-20-2012, 04:35 PM   #6
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Calculating charge on Goodman SSZ14


Quote:
Originally Posted by zootjeff View Post

He's giving generic SC values. Which don' work on all heat pumps. And he is giving SC values for piston metering devices. Not accurate.

SC can and will vary as the coil frost up. So in humid areas, you won't get the SC value your looking or after 10 minutes of run time, due to frost build up.

Giving a target SC value of 8 to 12 means it could be over or under charged. I have seen them run much less, and much higher.

There are other ways to check. But, its still best to weigh in charge, and recheck/fine tune in the spring.

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