Leaking or Not???

[Alex_homeOwner]

Any help would be appreciated:

The contractor put pressure on two lines (used freon not nitrogen - acknowledges it was bad decision). Did it leak? The temperature drop was about 10-15 degrees outside and about 6-7 degrees inside.

Start P Ending P
110 91 (3/4" line)
90 81 (3/8" line)

Thanks!

Alex

[lirunaway]

(used freon not nitrogen - acknowledges it was bad decision) Pull it into a vacuum. 500 microns or better for 24 hrs.

[bmathews]

I will assume you are trying to isolate a leak in your system somewhere. Not sure why temperature is being checked or why freon is being used. Kinda chickensh7t in my opinion. Freon reacts to changes in temperature by changing its pressure. So what you put in at 9am when it is 55 outside @ 100psig at 4pm when it is 85 outside is now 125psig. You will accomplish absolutely nothing unless he is using a leak detector to try to find it. He has wasted his time and your time. You need to pressurize with nitrogen to about 150psig and let it sit to accomplish your goal. We do a lot of new construction and get more nails in our freon lines from the siding/stucco guys or the trim carpenters putting up shelves and I have to do this once a month.

[Alex_homeOwner]

Replacing unit (leaked before + 10 years old). Trying to determine if lineset is leaking or if can reuse it (upstairs, difficult to run new lines).

Line is isolated and temp was checked because if temp changes line pressure changes.

He just pulled a vacuum to 28 on the 3/4 line (the one with the largest pressure drop). Plans to install the inside coil then make decision on replacing line.

TY for the comments - any more insights are appreciated!

Alex

[ckr74]

Not trying to be rude but maybe you might be better off with another service tech.

[just_opinion]

Alex,

If one introduce freon into the line and only VAPOR, then temperature is not the factor at all. Freon PT chart is for saturated temp, which include liquid and vapor of that particular freon. Thus, the idea of recording the temperature of the line and its pressure is incorrect, if the line contains only vapor.

Best to ask the contractor to use nitrogen or pull deep vaccum and left it for 24 hours.

[RandyRich]

I'm just a student, but we have been taught that pulling a vacuum on a system is not a good way to determine if there is a leak. According to what we've learned, if you pull a vacuum and the pressure rises, you probably have a leak, but if it doesn't, you may still have a leak. A vacuum of 500 microns exerts only a fraction of the pressure on the lines exerted by pressurizing to 150 psi and it exerts it in the opposite direction (from the outside in) whereas the leak will be from the inside out. Therefore, the best way to determine if you have a leak is to pressure test the system with nitrogen. Is that correct?

[elkhvac]

Not trying to be rude but maybe you might be better off with another service tech.

That is what I was thinking

[catmanacman]

refrigerant lines generally hold such small volume that if you pressure each line up with nitrogen for a hour you will know if it leaks. and also any tech or install crew without a nitrogen bottle is ??? and also did he use a recovery machine to remove the freon or did he just vent it???

[alex_in_fl]

Randy:

Both methods have benefits and drawbacks. Recommend you learn both for that reason.

PV=nRT (ideal gas law). Therefore if line temp increases you might miss the leak unless it is a long test.

[lirunaway]

Not trying to be rude but maybe you might be better off with another service tech.

Now I'm thinking you might be better off with another teacher.

[sumdumguy]

Not trying to be rude but maybe you might be better off with another service tech.

not to mention, saving the hassle n just change out the line set...perocity leaks could be the problem in said line set