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    ball buster (14 Posts)

  • drhvac drhvac @ 2:20 PM
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    ball buster

    I replaced a R22 condensor.  Before evacuating with service valves closed, I pressure tested the lines and coil with 200 psi nitrogen. It dropped a little within 15 minutes. To make a long story short I couldn't isolate the leak, so I cut the lines at the evaporator, brazed a schraeder valve in and put 200 psi on the evap coil to see if it leaked. And while I was at it, I brazed the suction and liquid lines shut at the evaporator so now back at the condensor with the service valves still shut i could pressure test both lines individually with 200 psi. Here is the ball buster part, I went to lunch and came back, nothing dropped. WTF! Why would it drop when everything was connected, but not when eveything was tested individually? thanks in advance
  • Techman Techman @ 2:36 PM
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    B&B

    Was the evap in a cold attic? Then warmed up ?
  • drhvac drhvac @ 3:43 PM
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    I would think

    the pressure would increase as the attic got hotter. But we are talking within 15min. I could see the needle dropping. You must be talking about when I went to lunch and the pessure didn't budge. Still doesn't make sense. Temperature doesn't effect nitrogen pessue that much?
  • Techman Techman @ 9:19 PM
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    B&B

    The r22 cond unit had to be a "dry charged "cond unit. I assume you did something w/the dry charge? Did you leak check the service valves by taking the service valve caps off and leak testing down where the allen wrench goes ? Or maybe you are increadibly lucky and you cut out the leak when you cut the suction/liquid lines at the evap ? LOL! When the press dropped,did it come down to ,say, 175psig and stayed there or did the press keep on dropping?
    This post was edited by an admin on April 26, 2013 9:27 PM.
  • drhvac drhvac @ 9:42 AM
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    I left the

    nitrogen charge in the unit and kept the service valves shut. That was a thought I had of maybe the nitrogen was leaking through the service valves back in to the unit, but if that was the case, the same thing would have happened when I did the individual line testing. I put a little over 200 psi in the evaporator, suction line, and liquid line, and not one of them moved. The suc. and liq. lines was one cut about 6 inches off of the evap. coil, I pinched them off and brazed both of them.
  • Techman Techman @ 11:35 AM
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    BB

    Not leaking back into the unit, but leaking out thru the S.V. packing and into the air.More than once I've heard them leaking upon moving the "stem" from it's front seated to it's back seated position.
  • drhvac drhvac @ 12:50 PM
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    that is

    possible, but I think I did check them with bubbles. Its an American Standard unit, so those valves have been very reliable for me in the past
  • JStar JStar @ 5:21 PM
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    Leak

    Was it the TXV equalizing?
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  • drhvac drhvac @ 8:34 AM
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    piston

    When I pressure test, I open both sides of my gauges and feed the nitrogen in with the pressure regulator so that it is equal on each side of the valve, however this has a piston as a metering device.
  • unclejohn unclejohn @ 10:36 PM
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    Could have

    Leaked at your gauges. Temp will have no effect on the nitrogen. You had to open them when you did the soldering for the 2 pressure test and I'm sure when you re pressurized you made sure they were on good and tight.
  • drhvac drhvac @ 7:26 AM
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    I don't think so

    once I noticed it losing charge I refilled and double checked all the gauge connections, plus the gauges are brand new. Going back tomorrow to see if my pressures are still holding, let you know how i make out.
  • unclejohn unclejohn @ 11:37 AM
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    You said it

    Dropped a" a little " how much is that 195# 175#? Did you purge with the nitrogen first and then pressurize or just press. when there was still air in the system. Maybe if it was the latter that may explain the little drop.
  • drhvac drhvac @ 1:55 PM
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    it was

    about 3 -4 psi drop within about 20 minutes. Im pretty sure i purged the air out but may be I didnt. still nitrogen usually doesnt budge when there isnt a leak, 3 psi in that short amount of time is alot.
  • drhvac drhvac @ 7:50 AM
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    went back

    about 4 days later to finish. All the pressures held. I don't know what caused the pressure to drop that first time I checked before going through these extra steps. The only thing I noticed is when I cut the suction line to start repairing it, I forgot to let the pressure out and a bunch of oil came out. Can oil in a line cause nitrogen to change pressure a little? That is the only thing that I could think of. I got the vacuum down to below 500 microns and it held for 5 minutes, so everything is good to go. Very strange.
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