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Old 12-12-2012, 09:02 AM   #46
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Subcooling is way high -- Need Advice!


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Originally Posted by beenthere View Post
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.
Why does 125psi with the panel off indicate that the TXV was open? Since I had the TXV in ice water it should have been closed, right? Does that indicate a bad TXV? If I do need to replace the TXV, would it be a good idea to add a filter-dryer to the liquid line near the AHU to prevent clogging? (heat pump already has an integrated filter-dryer).

Maybe dumb question; is the black cap in the second picture above a low pressure port that I can use to take accurate readings for this purpose?

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Originally Posted by NiNe O View Post
Small tip, you can block off outdoor coil to raise head pressure while conducting these tests and simulate higher outdoor air temp.
Thanks, I have read that before but am unsure of the effect that would have on the system or my readings. Could I just wrap a plastic tarp around the sides of the unit?


Edit: I found the mfg specified replacement TXV but it is different than the one supplied. My current TXV is not adjustable while this one is adjustable. I will call Goodman if noone knows the answer to this, but are the non-adjustable types available? Edit Edit: I found this one but there's no picture or price listed, as I don't have an account with johnstone.

If the bulb/powerhead is the problem, can I replace just that or would the whole TXV need to be replaced? Or is it worth it to just replace the entire TXV?


Last edited by Ethereal; 12-12-2012 at 09:47 AM.
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Old 12-12-2012, 09:22 AM   #47
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Subcooling is way high -- Need Advice!


Cardboard would work, you don't want the pressure to rise enough to trip high pressure switch just enough to simulate summer operation.
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Old 12-12-2012, 02:49 PM   #48
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Subcooling is way high -- Need Advice!


125PSIG is 43F saturation temp for R410A. So the TXV was feeding. While the TXV could be sticking at times. that one test alone doesn't confirm that.

You can use that port to take pressure readings. but then you can't get the panel on like it should be to get a proper reading.

The power head can be replace.
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Old 12-12-2012, 04:00 PM   #49
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Subcooling is way high -- Need Advice!


According to the weather, it should be just a bit warmer this weekend. I'll plan on using the cardboard trick and properly test the TXV following this procedure: http://www.hvac.amickracing.com/TXV%...0Diagnosis.pdf.

It looks to me though like my TXV is not serviceable. The power head looks like it is pressed on, and there is no adjustment for superheat. I'll verify that for sure when I test it again.

Edit: The TXV is indeed not serviceable.

Last edited by Ethereal; 12-13-2012 at 09:49 AM.
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Old 12-16-2012, 04:19 PM   #50
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Ok I tested the TXV today and I found what seems to me to be pretty peculiar. Here are my results...

2. Start the system and cool the bulb in a container of ice water, closing the valve. As you cool the bulb, the suction pressure should fall and the suction temperature will rise.

Temperature did rise, up to about 44 degrees but pressure never changed! It was +/-1 degree of 126psi the whole time. I could hear what sounded like the TXV closing (it sounded like fluid with air bubbles in it being forced through a small orifice).

3. Next warm the bulb in your hand. As you warm the bulb, the suction pressure should rise and the suction temperature will fall.

Again, pressure stayed pretty much constant. Temperature did fall as expected, to 32-33 degrees. No more gurgling sound.

Aside from pressure not changing, I feel like this confirms that the TXV is ok based on what you guys have told me and what I have read. Does that sound reasonable?

I did use the "cardboard trick" and found a way to get the AHU sealed while taking measurements ---
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Old 12-16-2012, 04:49 PM   #51
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Subcooling is way high -- Need Advice!


Sounds like it is over charged.
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Old 12-17-2012, 12:18 PM   #52
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Well, I will hook the TXV back up and get another reading. After removing the TXV it was apparent that it was not installed correctly, so I'll make sure it has good contact and is insulated this time. Maybe if I am lucky that will solve the problem. If not, I'll probably just have someone come out to evacuate and recharge by weight, although I suppose I will need to do the conversion for the 5/16" to 3/8" line.
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Old 12-17-2012, 12:36 PM   #53
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I thought you weighed it in from the git-go? If you didn't than you could very well have over charged it waiting for the "text-book" reading you seem to be shooting for.
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Old 12-17-2012, 12:37 PM   #54
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I thought you weighed it in from the git-go? If you didn't than you could very well have over charged it waiting for the "text-book" reading you seem to be shooting for.
I didn't charge it at all, it came pre-charged for a 15ft lineset and I have a 20ft lineset so I figured that it should have been low if nothing else.
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Old 12-17-2012, 12:39 PM   #55
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Subcooling is way high -- Need Advice!


eliminate the 5/16" pieces. They could very well restricting the flow. tHAT WILL NEVER ALLOW YOU TO GET WHERE YOU WANT TO BE on press and temp. Could have caused you to overcharge cause it was showing low press.
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Old 12-17-2012, 12:45 PM   #56
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Did you read his post. He didn't charge it.
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Old 12-17-2012, 12:46 PM   #57
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eliminate the 5/16" pieces. They could very well restricting the flow. tHAT WILL NEVER ALLOW YOU TO GET WHERE YOU WANT TO BE on press and temp. Could have caused you to overcharge cause it was showing low press.

If my readings don't make sense after I replace the TXV, that might be my next course of action. Pump down and replace the 5/16. I have a second unit (R22) that also has 5/16" line while the mfg specifies 3/8". It has a 75ft run from the condenser to the AHU. Takes a while for pressure to equalize on that one but it does perform and measure as expected.

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Did you read his post. He didn't charge it.
I think what he is saying might still make sense, although from what I have read 5/16" shouldn't cause any issues.
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Old 12-17-2012, 01:04 PM   #58
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Subcooling is way high -- Need Advice!


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I think what he is saying might still make sense, although from what I have read 5/16" shouldn't cause any issues.
Don't bet on it. If the 5/16 is not reamed well, the flow thru it will be problematic....especially thru a long line. It can act a metering device b4 refer enters TXV.

I always put sight glasses on all my liq lines just b4 the Evaporator on long line sets to make sure I have a full liq line and no flash gas.
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Old 12-17-2012, 01:27 PM   #59
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Subcooling is way high -- Need Advice!


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Originally Posted by hvac5646 View Post
Don't bet on it. If the 5/16 is not reamed well, the flow thru it will be problematic....especially thru a long line. It can act a metering device b4 refer enters TXV.

I always put sight glasses on all my liq lines just b4 the Evaporator on long line sets to make sure I have a full liq line and no flash gas.
That's a good idea. I think that I'll measure the temp. at both ends of that liq. line. If it is offering any restriction I believe it should show up as a temperature delta.

TODO:
- Reconnect TXV bulb properly
- Measure LL temps to verify no restriction
- Run system, taking subcooling measurement again with cardboard over condenser

Last edited by Ethereal; 12-18-2012 at 12:18 PM.
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Old 12-17-2012, 01:33 PM   #60
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Subcooling is way high -- Need Advice!


Not always, if it's not flashing off at the time of your measurement there will be very little delta t.

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