Liquid line freezing

[todd s]

I am having a mental block, what would cause a liquid line to freeze? This is a residential 4ton split system. Someone just asked me this and I was at a loss - its early. Could you guys help me out?

[faith]

A leak... Normally a liquid line is hot to the touch. The liquid refrigerant is actually sub-cooled below saturation pressure to avoid "flash gas" from forming before the liquid reaches the orifice or TXV. However if a pressure drop occurs due to a leak, then the phase change from liquid to gas will consume massive amounts of heat energy... Does this make sense?

Also this is why you don't want liquid refrigerant being spilled on your skin or heaven forbid getting in your eyes... FROSTBITE!

Please wear eye protection any time you handle refrigerant, it is extremely dangerous in its liquid state.

[docholiday]

Originally posted by faith
A leak... Normally a liquid line is hot to the touch. The liquid refrigerant is actually sub-cooled below saturation pressure to avoid "flash gas" from forming before the liquid reaches the orifice or TXV. However if a pressure drop occurs due to a leak, then the phase change from liquid to gas will consume massive amounts of heat energy... Does this make sense?

A leak causing restriction? Also I dont think the liquid line should be hot, maybe were just mincing words but warm would be a better description. I would say slightly above ambient would be a better description of how it should feel. (of course we use proper tools not feel).

A restriction such as a kink, plugged drier, or other would cause the liquid to have a pressure drop at the point of restriction (provided there is still some flow). The restriction acts as a metering device. Since refrigerant follows a pressure temperature relationship, the combination of gas and liquid present determines the saturation temperature. At this point there is no superheat or subcooling. A leak on the otherhand will not make the liquid line freeze.

[old yeller]

Actually, if a leak were to lower the overall freon level, the liquid column could not be maintained, and the freon would change states before it could get to the evaporator causing the liquid line to act like the evaporator out in the wide open air.

I think that is what he meant by leak.

Please feel free to correct me if this is not true.

[Jultzya]

Think about it, if you had that big of a leak...

You would have never been able to pressurized the line with enough 'liquid refrigerant' where this would ever happen.

And the small leaks will not cause a freezing liquid line.

[docholiday]

Yeller...

No, flash gas caused by liquid refrigerant having no subcooling would not cause cooling. you cant subcool refrigerant (in volume) while it is in both liquid and vapor state, otherwise metering would not work either.

[todd s]

I got a little more info now, two techs have been there. First one added about 8oz of r22 and said it was okay, that was about 3 weeks ago and we've been in a heat wave - customer said that the unit ran okay untill the other day. Todays tech thought there was a restriction with the return air(16"flex) and that the condenser fins were pretty bent. I'm trying to put more info together. Thanks for the responses.

[docholiday]

If the condenser fins ae bent your liquid linewqould get wrmer, not cooler. The return air would cause a lower suction but lower superheat as well. Ultimately this would have nothing to do with the subcooling.

Maybe, just maybe, someone said freezing liquid line and meant suction line.

[heatpumpjesus]

i go with DOC, probably factory drier in condensing unit clogged - had many yorks do this a few years back.

[bornriding]

Doc is right ! It must be a restriction
If this really is a cold liquid line, then allow the frost to melt, start the unit, and where the frost first starts to appear is where yur restriction is.

[igwt777]

There could be many reasons, but I will check for a LL restriction. Look for OEM filter drier clogged or aftermarket if installed, what brand and model is this system.

I will do same as [b]bornriding{/b] said:

shut down system and let it melt
restart system an look where frosting start
There is your restriction.

[todd s]

Unit is a Tempstar 4ton approx 9yrs old. Techs did not write down model #.

[docholiday]

Really need the model but I doubt a 9 year old tempstar had a factory drier installed. Is this a a/c or h/p? (a heat pump has a few other things in the line).