who is right or wrong

[will173]

Hi my name is will only three years in the trade. I was working on a 1/2 copeland that's air
Cooled. This unit runs a two fan evap. I got a service call on the unit because it iced up. The the building super defrosted the coil and it was at temp when I arrived.
So I checked the the pressure and found the unit was in vacuum and oil all over the service pvvalves cap. To me it was an indication the the leak was coming from this area so I recovered the refrigerant and repaired the flare nut with a new one here's the problem I leak tested the unit with nitrogen 100psi waited for five minutes and no leak walked away for fifteen then found pressure miss. I thought maybe it was my hoses and vacuumed the unit for fifteen then let it sit and I didn't loose any pressure who is right the vacuum or the nitrogen.

[Jettmac]

What micron did it hold and for how long?

[Jettmac]

What I've done in the past when nitrogen testing small stuff was to leave the system as it would operate (no gauges, all caps on, valves closed), then pressurize hoses back to where I left the system before cracking it to check it out.

[Frosted]

The Nitrogen is probably correct...if you did not use a micron gauge to test your vacuum, how do you know you weren't losing vacuum and it just wasn't showing on your compound gauge yet? Lot of microns between lets say 28" and 29" hg don't you think?

Mike...

[james122964]

Will, not withstanding the vacuum level, you should have put a trace of refrigerant in the system, then pressurized and checked for leaks with your detector, and leak test bubbles. Also, a lot of valves leak at the stems, because the pack nut is loose/warn.

If you lost pressure it may be a leak or it may have still be equalizing, so the net pressure was less.

Also, depending on the refrigerant, you could be running in/near vacuum and everything is OK on a freezer.

Jim

[dave1234]

Hi my name is will only three years in the trade. I was working on a 1/2 copeland that's air
Cooled. This unit runs a two fan evap. I got a service call on the unit because it iced up. The the building super defrosted the coil and it was at temp when I arrived.
So I checked the the pressure and found the unit was in vacuum and oil all over the service pvvalves cap. To me it was an indication the the leak was coming from this area so I recovered the refrigerant and repaired the flare nut with a new one here's the problem I leak tested the unit with nitrogen 100psi waited for five minutes and no leak walked away for fifteen then found pressure miss. I thought maybe it was my hoses and vacuumed the unit for fifteen then let it sit and I didn't loose any pressure who is right the vacuum or the nitrogen.

The following story is true- the names have not been changed... screw the innocent. Last year towards the end of the cooling season, actually it was more like November, i replaced a compressor on a rtu. I brazed her in, pulled a vaccumm for a few hours (I take care of this bldg exclusivley and had plenty to do). Evacuated all till my gages bottomed out, I know I should use a micron gage :couchhide: I disconnected the contactor and fuses to prevent starting in a vaccumm for what ever reason even though its LPC protected- I also know better then to leave in a vaccumm. I put it on the back burner and let it sit in a vaccumm until early May since 2 stgs of mech cooling not needed until then. Checked my vacuumm- gages bottomed out. Seemed to have held for almost 6 months no problem. Evacuated a little more and pressurized with Nitrogen until the next day when Id be charging it up and putting back into service. Lost signifigant amount of pressure and ended up finding a pin-hole coil bend sleeve leak. All Im saying is that it held an almost "perfect" vaccumm for almost 6 months (which I should not have done) and lost a nitrogen charge overnight. Speck of dirt, armaflex or whatever can and will plug a small leak in a vacumm. Pressurizing with nitrogen is the best.. no only way to go IMO. Yes it sucks draggin a drum of nitrogen up the roof but so do call backs over a recently serviced leaky system. For whatever all that is worth.

[cjpwalker]

Perfect vacuum which is not possible to achieve would be 14.7 psi below 0 psig (give or take). You wouldn't perform a leak search with 15 psig in the system because it would never show up, right?

[hvac wiz 79]

Hi my name is will only three years in the trade. I was working on a 1/2 copeland that's air
Cooled. This unit runs a two fan evap. I got a service call on the unit because it iced up. The the building super defrosted the coil and it was at temp when I arrived.
So I checked the the pressure and found the unit was in vacuum and oil all over the service pvvalves cap. To me it was an indication the the leak was coming from this area so I recovered the refrigerant and repaired the flare nut with a new one here's the problem I leak tested the unit with nitrogen 100psi waited for five minutes and no leak walked away for fifteen then found pressure miss. I thought maybe it was my hoses and vacuumed the unit for fifteen then let it sit and I didn't loose any pressure who is right the vacuum or the nitrogen.

that i.m.o is not a good tool for leak checking a system

[luskys a/c]

I like to pressurize the system in two parts. high side and low side with same pressure #120psi . That way the equalization takes less time through the compressor. I need an hour no less to be totally sure there are no leaks. If it drops even 1 psi you have a leak somewhere. If your at a dead end in finding your leak then you can isolate your system and pressure checking section by section. I know you can do it!

[dave1234]

Perfect vacuum which is not possible to achieve would be 14.7 psi below 0 psig (give or take). You wouldn't perform a leak search with 15 psig in the system because it would never show up, right?

Unsure if this is a shot at me or not but im well aware of the technical definition of a perfect vacuum. I only used that term (perfect-couldve worded differently) and put it in paranthesis to emphasize the fact that the coumpound gage stayed bottomed out for nearly 6 months and yet didnt hold a standing pressure test overnight.

[dave1234]

I like to pressurize the system in two parts. high side and low side with same pressure #120psi . That way the equalization takes less time through the compressor. I need an hour no less to be totally sure there are no leaks. If it drops even 1 psi you have a leak somewhere. If your at a dead end in finding your leak then you can isolate your system and pressure checking section by section. I know you can do it!

X2. The best way to go when high-low can be isolated.

[derek989]

How much pressure did it drop?
Did you vaccum before you pressurized? I ask this because if there is refrigerant left in system would it change your sitting pressure if ambient conditions change. Does anybody have any thoughts on that.

[dave1234]

How much pressure did it drop?
Did you vaccum before you pressurized? I ask this because if there is refrigerant left in system would it change your sitting pressure if ambient conditions change. Does anybody have any thoughts on that.

when the OAT drops below the saturation temp of the gas and it condenses. If there where 5psi of residual vapor pressure of oh say 404. 5psig 404= around -40*F. If I had 5psi (superheated) vapor left in the system at say 10*F and charged with nitrogen if the OAT rose there should be no change in refrigerant pressure since its already superheated vapor and only increases temp but not pressure. If the OAT drops below -40* (the saturation temp) the gas condenses and the P/T relationship is re-established. I hope that's all on point.:o anybody else?

[luskys a/c]

How much pressure did it drop?
Did you vaccum before you pressurized? I ask this because if there is refrigerant left in system would it change your sitting pressure if ambient conditions change. Does anybody have any thoughts on that.

I agree with Dave , If you have enough refrigerant in the system the standing press. will change with the temp swing during sunset or sunrise . I would go with the standing pressure with out a ref. charge in it first just to eliminate that.

[Refer wrench]

The following story is true- the names have not been changed... screw the innocent. Last year towards the end of the cooling season, actually it was more like November, i replaced a compressor on a rtu. I brazed her in, pulled a vaccumm for a few hours (I take care of this bldg exclusivley and had plenty to do). Evacuated all till my gages bottomed out, I know I should use a micron gage :couchhide: I disconnected the contactor and fuses to prevent starting in a vaccumm for what ever reason even though its LPC protected- I also know better then to leave in a vaccumm. I put it on the back burner and let it sit in a vaccumm until early May since 2 stgs of mech cooling not needed until then. Checked my vacuumm- gages bottomed out. Seemed to have held for almost 6 months no problem. Evacuated a little more and pressurized with Nitrogen until the next day when Id be charging it up and putting back into service. Lost signifigant amount of pressure and ended up finding a pin-hole coil bend sleeve leak. All Im saying is that it held an almost "perfect" vaccumm for almost 6 months (which I should not have done) and lost a nitrogen charge overnight. Speck of dirt, armaflex or whatever can and will plug a small leak in a vacumm. Pressurizing with nitrogen is the best.. no only way to go IMO. Yes it sucks draggin a drum of nitrogen up the roof but so do call backs over a recently serviced leaky system. For whatever all that is worth.

WOW. That is crazy!!!!!! I would have bet my family jewels there was no leak. I guess i havent seen it all!!

[Frostmonkey74]

I have seen a similar situation. A unit hold pressure test for 24 hrs, holds a vacuum according to a micron gauge, but looses some or all of it's charge after start up, due to a thermal leak. Those are hard on confidence!!

[infinitend]

I ran into a situation once where I could pull a good vac but the unit would not hold pressure. The leak I eventually found was acting like a check valve.

[Snapperhead]

I've never trusted vacuum as a test for leaks, its only for removing moisture and air.

Nitrogen to 250 psi with bubbles is your friend and will never lie :yes:

[markettech]

So I checked the the pressure and found the unit was in vacuum and oil all over the service pvvalves cap. To me it was an indication the the leak was coming from this area so I recovered the refrigerant and repaired the flare nut with a new one.....

Will, I'm amazed you made it almost a year without having someone call you out on the above statement.

Oil on a cap (or anywhere else for that matter) is not an indication of a leak....it is an indication of oil.

Not saying the presence of oil should be ignored as it can be a great way to quickly focus in on an area of concern.

A visible breech of an otherwise sealed system is an indication of a leak. A soap bubble reaction is an indication of a leak.

Everything else is simply a guessing game......a game that you will most likely lose at more often than win.