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Old 02-26-2011, 10:23 PM   #1
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TXV and superheat


Any one have good idea on what would cause a TXV adjustment to make no different in the measured superheat? I get 0 degrees with it fully open and 3 degrees with it full closed. Bulb is directly on suction line and in the right position.

I've read there could be something in the valve body but I want to exhaust all other possibilities before I go down that road.

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Old 02-26-2011, 10:38 PM   #2
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TXV and superheat


Poor air flow? Wrong valve?

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Old 02-27-2011, 12:55 AM   #3
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TXV and superheat


For TXV you measure subcooling.

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Old 02-27-2011, 06:42 AM   #4
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TXV and superheat


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For TXV you measure subcooling.
Some OEM manufacturers use both to set up their systems. SH should be checked on all TXV systems.

SC on a TXV only indicates if the TXV is receiving a solid column of liquid, not if the charge is correct or if the TXV is feeding enough or too much refrigerant to the evap.
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Old 02-27-2011, 07:59 AM   #5
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TXV and superheat


Need lots of patience when setting controls on HVAC equipment. Don't happen immediately.
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Old 02-27-2011, 08:34 AM   #6
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TXV and superheat


Check your subcooling and see if your possibly low on gas. Could be possible your expansion valve isn't getting enough liquid to it. Also I would make sure you are checking it with the correct conditions. ie fully loaded and a warm day.

What kind of refrigerant system is this?
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Old 02-27-2011, 11:46 AM   #7
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TXV and superheat


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Originally Posted by Hubcap626 View Post
Check your subcooling and see if your possibly low on gas. Could be possible your expansion valve isn't getting enough liquid to it. Also I would make sure you are checking it with the correct conditions. ie fully loaded and a warm day.

What kind of refrigerant system is this?

I have a sight glass right before the TXV. I set the txv to he middle of the range. This is a 2.5 ton system and the txv is suppose to cover 2-3 ton. I charged until there was liquid in the sight glass with fan on high speed (1000 cfm). I was getting 1 degree super heat, I adjusted the txv all the way to increas superheat and got 2 degree. It is acting like the bulb isn't sensing the temperature. I'm going to try putting the bulb in ice water to see if it will restrict the flow.


I forgot to check my temperature drop so I'll do that next time I look.

This is a 410a 2.5 ton system.
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Old 02-27-2011, 11:49 AM   #8
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TXV and superheat


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Originally Posted by JJboy View Post
For TXV you measure subcooling.
Here are my charge instructions. Basically it says adjust TXV to super heat of 8, then charge to subcool 7.

3. Check subcooling and superheat. Systems with TXV application
should have a subcooling of 7 2 F and superheat
of 7 to 9 F.
a. If subcooling and superheat are low, adjust TXV to
7 to 9 F superheat, then check subcooling.
NOTE: To adjust superheat, turn the valve stem
clockwise to increase and counter clockwise to decrease.
b. If subcooling is low and superheat is high, add charge
to raise subcooling to 7 2F then check superheat.
c. If subcooling and superheat are high, adjust TXV
valve to 7 to 9 F superheat, then check subcooling.
d. If subcooling is high and superheat is low, adjust
TXV valve to 7 to 9 F superheat and remove charge
to lower the subcooling to 7 2F.
NOTE: Do NOT adjust the charge based on suction pressure
unless there is a gross undercharge.
4. Disconnect manifold set, installation is complete.
Subcooling Formula = Sat. Liquid Temp. - Liquid Line
Temp.
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Old 02-27-2011, 12:46 PM   #9
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TXV and superheat


Why are your temperatures?
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Old 02-27-2011, 02:00 PM   #10
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TXV and superheat


0 degrees superheat will ruin your compressor. Post suction and discharge pressures. Post liquid line and suction line temps. Post number on TXV.
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Old 02-27-2011, 02:10 PM   #11
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TXV and superheat


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0 degrees superheat will ruin your compressor. Post suction and discharge pressures. Post liquid line and suction line temps. Post number on TXV.
Now how are we gonna read the number if he post it on the TXV. Wouldn't it be better if he post them her instead.
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Old 02-27-2011, 02:17 PM   #12
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TXV and superheat


Small pen and zoom lens?
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Old 02-27-2011, 02:20 PM   #13
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Small pen and zoom lens?

ROFL... I knew I bought that 2,000,000 MM zoom lens for a reason.
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Old 02-27-2011, 06:28 PM   #14
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TXV and superheat


is this really DIY? Just a question to throw out there as you need a license to handle refrigerant..............
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Old 02-27-2011, 07:27 PM   #15
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is this really DIY? Just a question to throw out there as you need a license to handle refrigerant..............
There is no license required to handle refrigerant.

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