Stuck txv

[Bigdtown]

So in ac my high side pressures were pretty normal, but my low side was about 30 psi (410 a system). All my spider legs are freezing up and so I took the bulb off of the suction and put a wet towel on it then I went back up to my guages and my low side was still sitting on 30psi, not hunting at all. I diagnosed a stuck txv. Do you agree?

[Bigdtown]

wet, warm towel that is.

[hvaclover]

sounds like to me

[Milk man]

Yes. When you purged your high side hose, was there a lot of liquid.

[Bigdtown]

yeah there was actually. Tons. the remnants of what the evaporator was storving for I presume.

[freonrick]

what was your subcooling?

[Bigdtown]

didn't check superheat or subcooling due to the fact that I couldn't get the txv to hunt. Probably should have but didn't. I can tell you that the high side was pretty much spot on for what Lennox said it should be.

[freonrick]

your subcooling would have told you if you was stacking freon in the condenser or low on gas.

[hvaclover]

Well, I would agree that while this is an obvious restriction based on the info you provided, a SH and SC check should always be performed.

[Bigdtown]

I agree. That is only the second stuck txv that I have come across and will remember to do a sh and sc check next time and will in fact do one on this unit before I begin the work of changing it. I would think that the superheat would be more important to the diognosis than the subcool, am I wrong?

[zw17]

I always use a cup of warm water and ice water to see how the TXV reacts but I suppose a warm/ice cold wet towel would work and be a little bit easier to handle.

[Bigdtown]

your subcooling would have told you if you was stacking freon in the condenser or low on gas.

oh, right on. good point. Thanks.

[hvaclover]

I agree. That is only the second stuck txv that I have come across and will remember to do a sh and sc check next time and will in fact do one on this unit before I begin the work of changing it. I would think that the superheat would be more important to the diognosis than the subcool, am I wrong?

No, the SC is most important in this case...the evap is going to be starved and SH will be high...

[Bigdtown]

No, the SC is most important in this case...the evap is going to be starved and SH will be high...

gotcha.

[PM Heat n Cool]

Check superheat and subcooling....if both are high its most likely the txv or some kind of restriction

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[Bigdtown]

just a little update here...I checked subcooling and it was pretty much right on, as was my approach method. Suction was still sitting at 30psi so I went ahead and changed the TXV and after that the pressures were perfect. Don't really know why but it in this case it seems subcooling could not be trusted.