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  1. #1
    Join Date
    Jun 2013
    Location
    Atlanta, GA
    Posts
    41

    Cold Tech Prep table problem

    Hello again. I am having a problem with a prep unit and need a little advice. Heres the history on the unit: Cold Tech prep unit, 134a, cap tube system. New compressor 2 years ago, old one locked up. Been working fine until a month ago. Complaint was unit would stop cooling, they would unplug unit for an hour or so then plug back in and it would work fine for a couple of weeks then repeat itself. I checked it, found a small leak where filter drier and cap tube meet. Recovered, replaced filter drier and cap tube, pressure tested good, pulled vacuum and charged with 9 oz. Heres where the problem is: Pressures are 85psi static, running: 6psi on the suction side and 30psi liquid side, the filter and the cap tube are frosting. I actually have frost from the filter all the way up the cap tube and into the evaporator about 2 inches where it goes from cold to warm. I'm thinking ok, blocked evap. Recovered again, removed evap and blow out with nitrogen, put it back together. Pump nitrogen in low side, it will hold 110 psi for 2 hours, pump nitrogen in high side to 120psi and will quickly leak down to 80 psi. As fast as the high side pressure is dropping you would HAVE to be able to hear a leak... No external signs of leak at all. Tried to pull a vacuum on both high and low sides together. If I pull vacuum on low side only the high side gauge INCREASES in pressure to 30 psi. If I pull vacuum on low side only it will hold vacuum. Micron gauge is all over the place. What could I be missing. Be kind please, I'm new to commercial.

    Thanks................

  2. #2
    Join Date
    Oct 2012
    Location
    Wisconsin
    Posts
    4,430
    Where abouts on the system is your high side gauge hooked to. Is it hooked to a tap on the outlet of the drier. 30psi liquid is almost impossible, which has me wondering if there is a restriction upstream of where your gauges are hooked to.

  3. #3
    Join Date
    Jun 2013
    Location
    Atlanta, GA
    Posts
    41
    It is on the tap on the drier. The tap is on the inlet side of the drier. Whats really bothering me is that I cant get the high side to hold pressure or a vacuum but the low side is the exact opposite.

  4. #4
    Join Date
    Oct 2012
    Location
    Wisconsin
    Posts
    4,430
    Just thinking out loud here.

    Perhaps there is a restriction in the liquid line or somewhere in the condenser. You are pressurizing the drier with 120psi, and it is slowly bleeding into the condenser since the line is restricted.

    Your high side and low side are connected. If you have 110 psi in the low side, it should flow back through the cap tube into the high side and equalize out.

    If the low side holds for two hours but the high side does not hold at all, I'm thinking there is something plugged up/restriced.

    Any way to braze a tap in the discharge line and try and blow nitrogen through the condenser to see if its restricted.

    Also, you said you are new, and chance you brazed the inlet to the drier shut, or brazed the cap tube shut when you put the new dryer in. Not trying to be mean, but I've seen that happen, just trying to help.

    Good Luck -Mike

  5. #5
    Join Date
    Jun 2013
    Location
    Atlanta, GA
    Posts
    41
    Thanks Mike. I did double check before I cut the inlet of the filter drier and brazed the liquid line in, I pumped nitrogen in the filter tap through the cap tube to make sure I didnt get any Sil-phos in the end of the cap tube. The cap tube is the proper size and length as the original and I cut it with a cap tube cutter so the ends are good. Nitrogen flows beautifully through it. I'll check the condenser tomorrow when I get back there. This thing has been giving me hell for 2 days now, dont want to be married to it. Its not my type.......

  6. #6
    Join Date
    Oct 2012
    Location
    Wisconsin
    Posts
    4,430
    Not saying this is the case, but just something to keep in the back of your head.

    If there is any debris in the system, it will cause you a lot of problems in the future. Something could be wrong with your compressor that caused it to break apart and send pieces of it out into the system.

    The condenser coil could have been poorly maintained, and not cleaned, and your system could have overheated the poe oil and baked it, and that is plugging something up.

    If you do find a line is restricted, you probably want to drain the oil out of the little compressor and see what that looks like.

    I could be wrong and there could be something completely different too.

  7. #7
    Join Date
    Jun 2013
    Location
    Atlanta, GA
    Posts
    41
    Yea, I might just go ahead and put a condensing unit in it and be done with it.

  8. #8
    Join Date
    Oct 2011
    Location
    Chicagoland Area
    Posts
    4,853
    Are you 100% sure it's not your gauge or hose leaking? My guess is a leak in the discharge line or coil somewhere.
    Officially, Down for the count

    YOU HAVE TO GET OFF YOUR ASS TO GET ON YOUR FEET

    I know enough to know, I don't know enough
    Liberalism-Ideas so good they mandate them

  9. #9
    Join Date
    Oct 2009
    Location
    Raleigh, NC
    Posts
    802
    I think you might want to look at the braze at the inlet of the drier. It sounds like it might be brazed closed.

  10. #10
    Join Date
    Jun 2013
    Location
    Atlanta, GA
    Posts
    41
    I'm using a new JB analog manifold set with some new yellow jacket hoses but I'm going to pull out my Testo 570 with my new Appion hoses and see if that makes a difference. I pulled the whole condensing unit out and have it on a bench so I can narrow things down. I will also recheck the drier connection. Thank you all for the tips. Any input is greatly appreciated.

  11. #11
    Join Date
    Jul 2011
    Location
    Lehigh Valley, PA
    Posts
    471
    Pump nitrogen in low side, it will hold 110 psi for 2 hours, pump nitrogen in high side to 120psi and will quickly leak down to 80 psi
    If you pressurize the high side to quickly to 120psi, the nitrogen will migrate through the cap tube into the evap & compressor. If you go in the low side, nitrogen will work it way back into the high side. Are you watching both gauges at the same time? Sounds like you are doing something wrong or have a bad hose or something.

    With a 9oz capacity, you should be using a low side stubby and a short hose to charge directly from your drum & scale to your high side filter dryer schreider valve . Weight in 10oz, quickly shut your valve on your drum and allow it to equalize for 5 mins. ( I am assuming the hose will hold 1 oz if it is a single hose, no manifold)
    Remove your charging hose quickly without losing gas and attach your high side stubby and turn on the unit.

    I just did a small freezer yesterday holding 7oz. using this method after installing a compressor & cap tube & .032 cap filter

  12. #12
    Join Date
    Sep 2008
    Location
    Western PA
    Posts
    25,946
    A typical manifold hose holds 0.33 ounces of LIQUID R134a per foot at 70 degrees.

    The amount of vapor is, essentially negligible.

  13. #13
    Join Date
    Mar 2013
    Posts
    44
    Or throw a stubby on the drier port, and feed nitro throw your suction side port (assuming its at the compressor), use your nitro regulator to balance in 150 psig. watch suction stubby raise to 150. shut off nitro tank, and see if suction drops at all in 20-30 minutes. if it doesn't, your manifold trolled you..

    From the suction port, it will back feed right back through the evap, through the cap tube, right into the drier and condenser and should hold, if all goes well. if it does in fact drop. Yeah your leak is on the high side. toss a bit of 22 in there with the nitro and H10 your way to success. purge, patch, evac, charge, start, go home, have a beer. Cheers.

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