# Liquid line restriction



## SpaceTime (Jul 28, 2016)

Hi All, 

My unit does not seem to be cooling. Had someone come take a look at it, and here are the tech's notes from troubleshooting:



> Client indicates system does not cool. When checking the system over the pressures were 146 low and 234 high super heat was 38 and subcooling was 0. The liquid line was sweating at the evaporator coil . Checked temperatures across the filter drier and got a 3 degree difference across it. Also have a 10 degree temperature difference from the liquid line at the evaporator coil and the liquid line at the condenser. Need to quote client to replace filter drier, and to also check the capullary tube to. The filter drier is built into the the liquid line in side the condensing unit.


Based on this, he indicated that he was pretty sure that the filter dryer is clogged up because there should not be any temp difference across the filter dryer. 

Now my question is, could the filter dryer be restricting flow or could it be the liquid line from the condenser to the evaporator?

Follow up question is that the filter dryer is inside the condensing unit. It can be gotten to it easily, but can it be replaced? I don't want to buy a new condensing unit just to address a clogged up filter dryer.


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## sidejobjoe (May 30, 2014)

3 degree drop over the filter/drier is pretty damning..... I'm not a pro but I think 3 degrees is a pretty big deal (i.e. really restricted). 

The part that sucks is the drier is before the service valve....so he will need to recover all of the refrigerant, replace it and then put it all back in. 

Not sure how he plans to do it but if it was my unit, I would put the drier in after the service valve and splice together the connection inside the condenser..... saves pain in the a$$ in the future.


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## Plumber101 (Feb 25, 2009)

From the pressures show I would assume that this is a 410a system. I would also want to know what sub-cooling is but I would have add freon and decreased the super heat to get the cooling back. I think the low and high pressure are both low and that all you need is freon. Think you had a young tech. I'd get a second opinion I would expect the low to be around 170-200 and the high 325ish. What was the outside temp?


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## SpaceTime (Jul 28, 2016)

Thanks sidejonjoe, I will suggest that if it comes to replacing the filter drier. 
@Plumber101, In his notes, he wrote the sub-cooling at 0. This is a 410a system. And the tech was young, he took notes called back at the office and spoke to seniors who guided him. The temp outside today was HOT, in the 90's F. 

I asked if the coolant was enough and he said, it looks OK, but with the restriction the numbers on his device could be off.


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## Plumber101 (Feb 25, 2009)

Then imho refrigerant is low.

Sub-cooling should be somewhere around 10

You add freon to decrease super-heat and increase sub-cooling.

I would bet that while the filter may be a little restricted that it is not the cause for not cooling and that adding freon will take care of your problem.

If I add over 1 1/2 lbs of freon I would do a leak check

Also if you had a restriction the high pressure would be higher and the low pressure would be lower. Just looking at both the pressures they are both low and by adding freon both pressure will come up.


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## BayouRunner (Feb 5, 2016)

A stopped up drier inside the condenser would not show higher pressures at the gauges. Because you are taking a reading after the restriction. a good clue would be after the ac runs for a while the drier might be sweating slightly, they don't always though but if you see that I would change it. I put mine outside the unit as well when I change one inside.


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## user_12345a (Nov 23, 2014)

having the liquid line sweat is not normal if the only problem is a refrigerant leak.


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## supers05 (May 23, 2015)

The filter dryer is plugged. Yes there could be other issues after that, but it's plugged. I would change it in a heart beat. (and I'm not that young) 2*f is textbook for diagnosinga plugged filter drier. 

With it plugged, it is pumping down so evap pressure will be low, and the liquid line after it would be in saturation. (0*F sub-cooling) 

A plugged filter drier is a symptom though. 

For a new unit, it could be just a wet or dirty install. If the temp difference disappears after you leave the unit off for a while and warm up the filter dryer, then it's moisture. 

If it's an older unit, (+10yrs) the oil and/or the compressor windings are breaking down. Then it's better to replace the whole thing. (if you were my customer I would give 0 warranty on a old compressor if you demanded the filter changed instead of a new unit.) 

Cheers!


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## beenthere (Oct 11, 2008)

From the info you posted, it sounds like the tech is correct.
At 146PSIG, R410A is at a saturation temp of 50.5°F(R410A systems are designed around a saturation temp of 45°F, which would be 130.7 PSIG). So it sounds like you have a TXV that is wide open due to being feed a combination of liquid and vapor, and the evap coil being warm.

R410A at 170PSIg would be at a saturation temp of 60°F. Which, while it could still cool your home some, it would remove little to no moisture from the air. Making your home feel worse then being outside.

The LLFD can be removed and a stub of copper tubing out in its place, and a new LLFD installed outside of the cabinet. That is the preferred method, but a new LLFD can be installed where the current one is.


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## SpaceTime (Jul 28, 2016)

Hey all, 

Many thanks for the advice/suggestions. This is really becoming a mystery. I've had 3 people look at this, and all 3 scratching their heads. This all started after I got a new evaporator coil installed due to a leak in the old one. After installing the coil, my system just never worked. 

The tech that installed it (tech #1), initially felt that there is a restriction in the liquid line. So, I got a second opinion from another company who initially felt that it was a filter dryer restriction based on the comment in my original post. The same company, sent out another senior tech who measured no difference in the filter dryer this time. 

His notes are:



> Cycled cooling for 2nd floor, checked refrigerant charge which was 120/200. Accessed unit in attic and found the liquid line condensating and cold throughout the entire run before it goes outside to the condenser, suction line was at room temperature. Superheat was at 30 degrees and no subcooling. Checked line temperatures before and after liquid line filter drier at condenser which was at 70 degrees as this rules out a restriction at the filter drier. It seems as if the metering device is not operating properly. Accessed evaporator coil, found it to be a piston type of metering device. But according to the name plate on the coil door, an orifice is NOT factory installed. Suspect that an orifice was never installed for metering device as this is a case coil replaced by another company last week. Client will be contacting other company that did the work to correct issues. Advised client that the refrigerant should be recovered completely, the correct size orifice to be installed, and a new liquid line filter drier installed, system to be evacuated properly, new refrigerant added to system to manufacturer specs and system to be checked for proper operation.


The person that installed the coil says the orifice was installed. So this brings me back to square one. Not sure what is exactly going on.


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## sidejobjoe (May 30, 2014)

SpaceTime said:


> found the liquid line condensating and cold throughout the entire run before it goes outside to the condenser, suction line was at room temperature.


This doesn't quite make sense.... If you really mean the liquid line in that quote, I would think it almost certainly means there is a restriction somewhere... a knink in the line, filter drier plugged etc... maybe even a restriction in the outdoor coil? Is the outdoor coil really cold/sweating at the bottom and warmer at the top? 

If you meant vapor/suction line as being cold all the way back out, then that is normal 


Perhaps a dumb question here but... is this a heat pump or just a straight A/C ?


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## SpaceTime (Jul 28, 2016)

sidejobjoe said:


> This doesn't quite make sense.... If you really mean the liquid line in that quote, I would think it almost certainly means there is a restriction somewhere... a knink in the line, filter drier plugged etc... maybe even a restriction in the outdoor coil? Is the outdoor coil really cold/sweating at the bottom and warmer at the top?
> 
> If you meant vapor/suction line as being cold all the way back out, then that is normal
> 
> ...


There is no heat pump @sidejobjoe. There is no TXV either. The notes are correct, the liquid line is cold. And when I say the liquid line, I mean the thin one with no insulation. 

So the liquid line on the outdoor is not cold, perhaps due to the ambient temp? In the in the inside of the attic the liquid line is cold as well as sweating. The outdoor coil in the condenser unit is also not freezing up. 

Regarding the restriction, should the pressure hold stable if there is one? According to tech #3, he said that his gauge was showing the pressure as normal and stable, therefore it may not be a restriction. Otherwise, I would see the pressure build up.


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## sidejobjoe (May 30, 2014)

He is measuring the pressure at the service valve.... so it may be reading OK (though he noted there is no subcool, but that could be kinda of OK with a low charge). 

The fact that the line is cold, so cold it sweats (below dewpoint), is the problem... liquid should never be doing that. 

You say that the liquid line outside is not cold.... by the service valve I presume? Are you able to follow every inch of it and find where it goes from warm to cold? It really seems like a kink in the line to me.... (I am not a pro)... I suppose the other possibility is that is plugged up with junk if the guy who installed your new coil didn't flow nitrogen when he brazed it together. 

Give all the facts... superheat is high and suction line is warm... the liquid line is so cold it is sweating etc... the evaporator is being starved of refrigerant.... and the there must be something causing a major pressure drop to get the liquid refrigerant down to a sat temperature below the dewpoint (and cold!).


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## SpaceTime (Jul 28, 2016)

sidejobjoe said:


> He is measuring the pressure at the service valve.... so it may be reading OK (though he noted there is no subcool, but that could be kinda of OK with a low charge).
> 
> The fact that the line is cold, so cold it sweats (below dewpoint), is the problem... liquid should never be doing that.
> 
> ...


That's the thing, I cannot follow the liquid line inch by inch, there's a portion of it behind the walls.


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## beenthere (Oct 11, 2008)

Just because there is no temp difference across the liquid line filter drier, doesn't mean its not restricting. You can have a 50 PSIG restriction, and not have a temp drop/difference across it.


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## supers05 (May 23, 2015)

Either the liquid line is kinked where it enters the house/ or in the walls, or the system is moisture ladden. 

This will present if the system runs for long durations. Moisture will cause the oil to become more viscous, causing a slight restriction in the filter-dryer. This restriction then starts to cool the oil, making things worse. This then will freeze the water with time as things get worse, and the temp difference grows. You turn the thing off, the filter drier warms, oil thins and will flow again, and the tech can't see the problem anymore, unless it's been running for a while first. 

A since it's r410A I'd recover it, change the filter drier, (probably over size it a bit) and replace with virgin refrigerant. (410 is relatively cheap) However, you could add a flared filter-drier to a manifold and let it pass though it (letting it flash to vapour down stream of the filter at a safe rate) I'd leave it like that for a day or 2 and recheck. 

If it's 

Cheers!


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## SpaceTime (Jul 28, 2016)

Thank you everyone who helped in getting to the bottom of this. The issue is finally corrected. 

The problem was...... the orifice metering device at the evap coil was installed backwards.


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## supers05 (May 23, 2015)

SpaceTime said:


> Thank you everyone who helped in getting to the bottom of this. The issue is finally corrected.
> 
> The problem was...... the orifice metering device at the evap coil was installed backwards.


Cool.... I was just telling the apprentice the other day not to screw that up.... Would have been something that I would have checked when the system was pumped down, but wasn't very high on my possible theories. 

Cheers!


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## SpaceTime (Jul 28, 2016)

supers05 said:


> Cool.... I was just telling the apprentice the other day not to screw that up.... Would have been something that I would have checked when the system was pumped down, but wasn't very high on my possible theories.
> 
> Cheers!


Thanks Supers05, I had to get another contractor to come down and have a fresh look at the system, the original contractor was just spinning wheels over 3 weeks of 4 troubleshooting attempts.

Is it really that hard to overlook this step? Why don't manufacturers just create the part so that it can only be installed 1 way? This would make it more fool proof.


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## supers05 (May 23, 2015)

SpaceTime said:


> ....
> Is it really that hard to overlook this step?


It's not a usual problem. But at 4 attempts, I'm surprised it wasn't pumped down and checked anyways. 



SpaceTime said:


> Why don't manufacturers just create the part so that it can only be installed 1 way? This would make it more fool proof.


That would make too much sense... I've asked the and question. Some models are very hard to reverse, some are way too easy... 


Cheers!


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