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Old 12-11-2012, 12:09 AM   #31
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Subcooling is way high -- Need Advice!


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Originally Posted by beenthere View Post
Or you just didn't take notice to the freeze up.

Past my bed time. Good night everyone.
You old guys ...Even Uncle does not retire this early and he's up before everyone else at work.

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Old 12-11-2012, 08:44 AM   #32
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Originally Posted by Patrick Eubanks View Post
Is this unit a nordyne product with a micro chanel coil?
No, Goodman units - 13 seer heat pump with matched variable speed AHU.

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Originally Posted by Patrick Eubanks View Post
Are you sure about that low side temperature reading?
Are you sure that there was no ice on the indoor coil?
I did not check for ice as the unit was running. I am pretty sure about the temp. reading, I took more readings yesterday evening, and I'll post them up in a minute.

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Originally Posted by beenthere View Post
You can put the water in a 55 gallon drum. It will still freeze. Only the mass where the water comes into contact counts.

Try a few experiments at your place.

The OP can do his own test, and he'll see how easy it is to freeze water in a vacuum.
That's ok, I will take your word for it! Here's some reference on that to keep you guys busy while I try to address my real question http://van.physics.illinois.edu/qa/listing.php?id=1597

Here are my results and observations from last night:

Test for excessive loading of the evaporator coil
I will try lowering the CFM and re-checking the subcooling. It is currently at 840CFM, I will go -10% to 756CFM and note the difference.

I lowered it to 700 CFM, and noticed a slight decrease in subcooling. The installation manual states that "most manufacturers recommend 350-450CFM per ton", but doesn't specifically say what Goodman themselves recommend. I'm at the low end of that range now though. Would it make sense to try decreasing it even more?

Check for air or non-condensables in the system:
Allow the condenser to cool to the outdoor air temperature. Check the pressure on the high side gauge and convert it to temperature using a PT chart. This saturated temperature should be within a couple degrees of outdoor air temperature. If this saturation temperature is any higher, I have air or non-condensables in the system.

See the image below. LL actual temp. was 65.7 degrees, while pressure was at 180.4Psi (63.2degrees saturation). Should this give me a warm fuzzy that I do not have air or non-condensibles in the system?



My P-T measurements were the following:

I have about 24degrees subcooling and 18deg superheat.

Testing the TXV
I haven't tested the TXV yet but did notice some peculiarities that I wanted to run by you guys. First of all, the sensing bulb was fully installed when I recieved the AHU. The install instructions say to install in after brazing in order to avoid overheating it. Well, since it was installed I just wrapped the line and the bulb well with soaked rags before brazing. How sensitive is this to damage by heat? Another thing I noticed is that the clamp holding the bulb on isn't very tight. It is screwed together fully but it seems that the clamp is just a hair bigger than it needs to be. Could this effect performance? The manual states to ensure a tight coupling to the suction line but that's impossible with the clamp they provided.

A couple other things that I noticed in the AHU: A drop of Blue liquid on the condensate pan under the suction line, and the top of the suction line on the evap coil where it is spun closed, there is some crusty crap going on... almost feels like sand or something.

Thanks for the help so far guys! I learn best by doing, and I learn far more from my failures than I do from success.

Last edited by Ethereal; 12-11-2012 at 09:24 AM.
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Old 12-11-2012, 09:21 AM   #33
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Subcooling is way high -- Need Advice!


Just my opinion, don't have any industry stats to check against, but I have found most TXVs today will not stand up the heat of brazing unless they are doused beyond reason to keep them cool.


Also, the TXV i have seen on the equipment I use (and others) have a LOT of bad and loose connection of the sensing bulb right from the factory.

Saw one manufacturer actually using a single zip on their blubs!

Coleman and other brands sell the TXV as an accessory and in those cases I will buy a Sporlan or an Alco TXV that has a robust mounting bracket. They will stand up to the heat if heat sinked with wet rags.
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Old 12-11-2012, 09:45 AM   #34
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Just my opinion, don't have any industry stats to check against, but I have found most TXVs today will not stand up the heat of brazing unless they are doused beyond reason to keep them cool.


Also, the TXV i have seen on the equipment I use (and others) have a LOT of bad and loose connection of the sensing bulb right from the factory.

Saw one manufacturer actually using a single zip on their blubs!

Coleman and other brands sell the TXV as an accessory and in those cases I will buy a Sporlan or an Alco TXV that has a robust mounting bracket. They will stand up to the heat if heat sinked with wet rags.
Ok, I think I'll test the TXV tonight (if my wife allows it ).

Is the following procedure adequate to verify that the TXV is working?

Test the TXV:
Check proper bulb position (between 10 and 2 o'clock). Take temp on suction line with TXV disconnected from suction line, with system running. Hold TXV in hand to warm it up and if TXV is working the suction line temp should change.
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Old 12-11-2012, 09:59 AM   #35
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Subcooling is way high -- Need Advice!


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Ok, I think I'll test the TXV tonight (if my wife allows it ).

Is the following procedure adequate to verify that the TXV is working?

Test the TXV:
Check proper bulb position (between 10 and 2 o'clock). Take temp on suction line with TXV disconnected from suction line, with system running. Hold TXV in hand to warm it up and if TXV is working the suction line temp should change.
To be honest, you are relying on text book instructions, and while they are a great general guide line, a salted tech has many more techniques in his bag of tricks that he has accumulated thru experience and trail and error to test system components.

But to give you an un-convoluted answer, yes, do what the instructions say. It will put you in the ball-park (lol...although I don't think you are the kind of person who will settle for "ball-park").
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Old 12-11-2012, 10:01 AM   #36
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PS

Never mention Superheat to a wife...she may think your getting "kinky".
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Old 12-11-2012, 01:35 PM   #37
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Subcooling is way high -- Need Advice!


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PS

Never mention Superheat to a wife...she may think your getting "kinky".
Lol, is that one of your "salted tech" tips?
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Old 12-11-2012, 04:19 PM   #38
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Subcooling is way high -- Need Advice!


Run system in cooling mode for 15 minutes or until system is stable. remove TXV bulb from line and immerse it in ice water. It should choke flow down and you should see the vapor pressure drop and SH increase. if you don't, the power head has most likely lost its charge.
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Old 12-11-2012, 04:29 PM   #39
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Subcooling is way high -- Need Advice!


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Run system in cooling mode for 15 minutes or until system is stable. remove TXV bulb from line and immerse it in ice water. It should choke flow down and you should see the vapor pressure drop and SH increase. if you don't, the power head has most likely lost its charge.
I'll try to get this done tonight. Can I do this in heating mode or cooling only? It may be only 50 degrees outside by the time I get home tonight.
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Old 12-11-2012, 04:34 PM   #40
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Cooling mode only.
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Old 12-11-2012, 04:40 PM   #41
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Cooling mode only.
Ah, the TXV is bypassed in heating mode... I guess I should notice some activity even with low ambient temps.
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Old 12-11-2012, 05:08 PM   #42
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Subcooling is way high -- Need Advice!


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Ah, the TXV is bypassed in heating mode... I guess I should notice some activity even with low ambient temps.
Yeah, just won't be as much.
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Old 12-11-2012, 06:46 PM   #43
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Subcooling is way high -- Need Advice!


I tried testing the TXV tonight but the indoor coil froze up. The liquid line remained unfrozen. Maybe this was because I had the cover of the AHU off? I got measurements while holding the sensing bulb in my hand and submerged in water but the readings didn't budge much (around 125psi and 8-10 degrees on the vapor line). Does this indicate a TXV problem or do I need to try again with the cover on and the bulb sticking out somehow?


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Old 12-11-2012, 06:51 PM   #44
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Subcooling is way high -- Need Advice!


Generally need to have the panel somewhat covering the opening so air continues to flow through the coil.

But if you had 125 with the panel off. that would indicate the TXV was open. Shouldn't freeze up the coil at 125 PSIG.
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Old 12-12-2012, 09:24 AM   #45
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Subcooling is way high -- Need Advice!


Small tip, you can block off outdoor coil to raise head pressure while conducting these tests and simulate higher outdoor air temp.

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