Expansion device: Capillary vs. TXV

[greg_mustang]

Hi,

Most split systems i have installed in my home have been with TXV.
Recently I have had the 'pleasure' of installing a cheap unit that uses a capillary as the throttling device for refrigerant expansion.
On this specific unit, I noticed that if the refrigerant is low, the output of the capillary freezes up, blocks, and causes the suction/discharge line to go all the way into vacuum.
On my other units, which had TXV, whether related or not, though I have had cases of low refrigerant, i never experienced the discharge freezing up causing negative pressure at liquid line.

Any comments? Is this really related to the capillary, and it is normal/common in your opinion?

I am not an hvac tech, just an engineer who likes to tinker. I absolutely always respect refrigerant handling.

Thanks,
Greg

 

[firebirdparts]

Freezups on low Freon (or while heating) have always been normal here in the US on capillary equipped heat pumps. I don't know if they are harder to do with TVX, but it seems like they would be. I'm also just an engineer that likes to tinker.

 

[elderstarr]

Freezing at the expansion device can be a sign of moisture in the refrigerant. Happens with a TXV or orifice.

Was there a filter drier installed?

Never seen a system freeze the expansion device closed due to low refrigerant. Refrigerant doesn't freeze. Likely something is contaminated in the system.

 

[LS6 Tommy]

Does the cap tube itself freeze, or just the evaporator at the cap tube exit?

Tommy

 

[karoc]

Pic would be nice of that area and I am asking for a reason, guessing this is a new system and a vacuum was pulled?

 

[greg_mustang]

Mini-split.
The expansion/throttling is done at the exterior unit, not at the evaporator.
When the refrigerant is low, the liquid line evaporates (if thats the correct term) too soon in the cycle, i.e. exactly at the output of the capillary, causing it to freeze up.
As refrigerant is added, the evaporation moves upstream into the lineset and before the evaporator, where it should be.
Hope this clarifies my hypothesis and understanding. If someone disagrees please let me know!
Thanks
Greg
Montreal - Canada
(Yes, up here too it gets hot as hell during some weeks of the summer, needing A/C).

 

[mcbane]

Mini-split.
The expansion/throttling is done at the exterior unit, not at the evaporator.
When the refrigerant is low, the liquid line evaporates (if thats the correct term) too soon in the cycle, i.e. exactly at the output of the capillary, causing it to freeze up.
As refrigerant is added, the evaporation moves upstream into the lineset and before the evaporator, where it should be.
Hope this clarifies my hypothesis and understanding. If someone disagrees please let me know!
Thanks
Greg
Montreal - Canada
(Yes, up here too it gets hot as hell during some weeks of the summer, needing A/C).

Ideally you want droplets of liquid refrigerant in most of the evaporator tubing, with the last of it boiling off close to the exit from the evaporator. In other words, evaporation of refrigerant should be happening IN the evaporator (not before); hence its name.


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