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Old 04-19-2011, 04:44 PM   #31
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Heat Pump or Newer high seer unit


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can you give me an idea what it should have been? I could be mistaken on what I was able to see, ballpark?

Are you coming to Texas anytime soon?
While that varies with both the indoor and outdoor conditions. The line temp should generally be several degrees warmer then the outdoor temp.

Sorry, but I no longer have any relative that live in Texas anymore.

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Old 04-19-2011, 04:52 PM   #32
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Heat Pump or Newer high seer unit


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Originally Posted by Ed C View Post
can you give me an idea what it should have been? I could be mistaken on what I was able to see, ballpark?

Are you coming to Texas anytime soon?

Where in Texas?
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Old 04-19-2011, 04:54 PM   #33
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Check this out Ed C

https://docs.google.com/viewer?a=v&p...MWE5ODdl&hl=en
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Old 04-19-2011, 04:57 PM   #34
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Heat Pump or Newer high seer unit


Suction pressure sounds OK to me but discharge sounds a bit low which may indicate an undercharge on a 8-10 SEER unit. I always add 10-20 deg F to the temp to get the pressure on a cool day if nothing else works. 83F in R22 =148 add 10 to 20 =158-168 psi. Impossible to tell w/o us being there and seeing the outdoor temp/humidity/cleanliness of coil/whether it was in the shade etc etc. Sounds OK to me. Ballparking never works well and we stopped recommending the beer can cold method of charging ACs years ago. Used to tell the newbies to keep adding freon until the suction line was cold and sweating like a beer can.
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Old 04-19-2011, 05:05 PM   #35
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Suction pressure sounds OK to me but discharge sounds a bit low. I always add 10-20 deg F to the temp to get the pressure. 83F in R22 =148 add 10 to 20 =158-168 psi. Impossible to tell w/o us being there and seeing the outdoor temp/humidity/cleanliness of coil/whether it was in the shade etc etc. Sounds OK to me. Ballparking never works well and we stopped recommending the beer can cold method of charging ACs years ago. Used to tell the newbies to keep adding freon until the suction line was cold and sweating like a beer can.
Yuri, could you check this document to see if I'm doing the calculations correctly? thanks

https://docs.google.com/viewer?a=v&p...MWE5ODdl&hl=en
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Old 04-19-2011, 05:12 PM   #36
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Heat Pump or Newer high seer unit


I really don't want to start you off on the wrong path with pressures and temps. Higher SEER ACs will run a lower head pressure than the older lower SEER units because they have larger coils and are more efficient. There is NO rule of thumb for anything anymore and you must as much as possible use the SPECIFIC chart that comes with the condensor to get the proper running pressures. It usually is on the back of the electrical box cover on the unit and sometimes can be faded or missing. Different brands run different pressures and I tell my apprentices to do checkups for a year and to document the different types of units and what pressures they run under different outdoor temps and loads and develop a sense for what is normal. Us older techs have done that for years and can recognize a lot of this from experience. You will to if you are diligent and do that.

For example where I am an older 8 SEER ac will run 175-200 psi head pressure 50 suction on a 70 deg day with 40%RH. A 10 SEER unit will run 150-175 and 40 suction on the same day. Also the furnace fans have got more powerful and that affects the suction pressure so there is NO rule of thumbs. You have to get familiar with the whole system. Duct size/type and capability of blower, metering device type etc.
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Old 04-19-2011, 05:33 PM   #37
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Heat Pump or Newer high seer unit


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Yuri, could you check this document to see if I'm doing the calculations correctly? thanks

https://docs.google.com/viewer?a=v&p...MWE5ODdl&hl=en
I don't like those documents to much. There subcooling is based on the head pressure temp and are saying to add or remove gas on that. Don't go buy that SH target as well. I don't know where hose documents are from but there is better info out there.
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Old 04-19-2011, 06:06 PM   #38
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I don't like those documents to much. There subcooling is based on the head pressure temp and are saying to add or remove gas on that. Don't go buy that SH target as well. I don't know where hose documents are from but there is better info out there.

Do you mind explain how you do SH and SC?
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Old 04-19-2011, 06:46 PM   #39
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I don't like those documents to much. There subcooling is based on the head pressure temp and are saying to add or remove gas on that. Don't go buy that SH target as well. I don't know where hose documents are from but there is better info out there.
Actually, the SH formula is pretty accurate. And matches most generic slide charts.
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Old 04-19-2011, 07:04 PM   #40
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Actually, the SH formula is pretty accurate. And matches most generic slide charts.
For SH i'm strong on it. I'm not comfortable with SC when I dont have the table in the the system.
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Old 04-19-2011, 07:22 PM   #41
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In that link they are using the old rule of thumb for 10 SEER equipment. Which was close. But 6, 8, and 10 SEER was forgiving, 12 SEER and higher is not forgiving. So hopefully no one really uses that SC BS in that link.

Low SEER units didn't remove a lot of heat from the refrigerant, so they had to raise the sat temp real high above outdoor temp to get it to change state, and remain liquid all the way to the indoor metering device.

SC is only required to ensure a solid column of liquid to the metering device(for those that didn't know its purpose).
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Old 04-19-2011, 08:11 PM   #42
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So to charging 13 seer or higher: calculate subcooling. Measure the high side pressure at the liquid-line service valve pressure tap. Using a pressure temperature chart, convert high side pressure to saturated temperature. Then simply subtract the liquid-line temperature from the saturation temperature of the refrigerant in the condenser to determine the subcooling.

The SC showing in the doc is ok to lower than 13 seer.



Quote:
Originally Posted by beenthere View Post
In that link they are using the old rule of thumb for 10 SEER equipment. Which was close. But 6, 8, and 10 SEER was forgiving, 12 SEER and higher is not forgiving. So hopefully no one really uses that SC BS in that link.

Low SEER units didn't remove a lot of heat from the refrigerant, so they had to raise the sat temp real high above outdoor temp to get it to change state, and remain liquid all the way to the indoor metering device.

SC is only required to ensure a solid column of liquid to the metering device(for those that didn't know its purpose).
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Old 04-19-2011, 09:18 PM   #43
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Heat Pump or Newer high seer unit


Subcooling increases efficiency a bit (on refrigerators they would solder the liquid line/capillary tube to the suction line to cool the liquid and increase efficiency) and it really is too keep a solid flow of liquid and no flash gas (what I get on chili nites) from getting to the orifice/metering device.

Hang in there JJ and ask good questions and you will build a database of fundamentals from each of the techs here.
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Old 04-19-2011, 09:30 PM   #44
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Heat Pump or Newer high seer unit


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Originally Posted by beenthere View Post
While that varies with both the indoor and outdoor conditions. The line temp should generally be several degrees warmer then the outdoor temp.

Sorry, but I no longer have any relative that live in Texas anymore.


Thanks I understand, and as far as when you are coming, I will leave that open!

Thanks
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Old 04-19-2011, 09:33 PM   #45
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Heat Pump or Newer high seer unit


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Suction pressure sounds OK to me but discharge sounds a bit low which may indicate an undercharge on a 8-10 SEER unit. I always add 10-20 deg F to the temp to get the pressure on a cool day if nothing else works. 83F in R22 =148 add 10 to 20 =158-168 psi. Impossible to tell w/o us being there and seeing the outdoor temp/humidity/cleanliness of coil/whether it was in the shade etc etc. Sounds OK to me. Ballparking never works well and we stopped recommending the beer can cold method of charging ACs years ago. Used to tell the newbies to keep adding freon until the suction line was cold and sweating like a beer can.

I understand about ball parking!

In the sun, condensor and coild recently cleaned when 2 lbs was added.

Thanks

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