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  1. #1
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    Casscade Systems



    I have recently taken a Job in the Biology Dept. at the University of South Carolina I take care of all there Lab Equipment. I am working on an Ultra Low Temp freezer. I had a leak on the accumulator on the 1st stage circuit. I ordered a new accumulator, installed it, pulled a vacum according to the factory specs. (held under 200 microns for 20 mins.) Charged the system again according to factory specs. Started the system, everything worked great untill the box started to get around -45C and then it stopped cooling. Now the factory tech support says that with a leak on the low side and with polol ester oil I have to change the compressor also. My question is how can I save a good compressor??? Can I change the oil in the compressor, flush the system, pull another vacum and be ok??? thanks for your help Eric



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    Re: Casscade Systems

    why did it stop cooling ,did a capilliary stick with moisture .problem with poe oil is that it absorbs moisture & holds it .definitly worth a try dumping out the oil ,refilling, evacuating breaking with nitrogen then repeat a few times and recharge.but you would want to be sure moisture was the problem

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    Re: Casscade Systems

    I am going by what the factory tech support told me . What would be the best way to tell if moisture is the problem
    The factory tech support is telling me that anytime there is a leak on the low side that the compressor has to be changed. just seems a waist to change a good compressor. I have purchased a new compressor and am going to try to clean up to old one and reuse it on another unit. I just wanted some ideas on the best way to do this or if anyone has run across this

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    Re: Casscade Systems

    attach suction gauge to system and run if moisture is present it will at some stage freeze in the capilliary and the system will drop into vacuum .key to this is system will appear normal at start up

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    Re: Casscade Systems

    Is this a revco? revco ultima and value series ie; ult and elt models have the second stage start in 15 minutes if the system is at -42 or if the system reaches -42 after that. what are your tc readings? what did you charge it with? why are you touching my children?

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    Re: Casscade Systems

    This system runs in a vacum anyway. If moisture is present the vacum will be abnormaly low when the moisture freezes and refrigerant flow stops. Thanks for your help, I have worked on very few of these units and a little unsure of myself.

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    Re: Casscade Systems

    the tcs are located in the front left behind the filter up on top. this is t type thermocouple and gives you readings at different points in the system. 1- 1st stage in to interstage 2- 1ststage out of interstage 3- 2nd stage evap in 4- 2nd stage evap out 5- is redundant with 4

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    Re: Casscade Systems

    Yes its a Revco ULT unit and the second stage did start around -42 but when th cabnet started getting cold it stopped cooling. It was charged with 134a and 404a weighted in according to factory specs. Great to meet you Captain Cascade I may have more questions for you

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    Re: Casscade Systems

    I did check the tcs but I have the reedings written down at the shop, I do remember #1 tc was around -42 -45 and the second stage started and all was well untill the cabnet temp started dropping then the tc# 1 temp started rising and the second stage dropped out

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    Re: Casscade Systems

    add 404a. dont let the head pressure go over 200. time the 1st stages pull down. with the high pressure switch for the second stage yanked (thatll keep it from runnin) if the 1st stage cant make -50 in 10 min (thats 1 and 2 tcs) you have a first stage that is unhappy with its station in life and wanted to be an artist or something.

  11. #11
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    Re: Casscade Systems

    those weights are never right. ever

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    Re: Casscade Systems

    the goal for your first stage head with the right mix of 134a and 404a will be 175 and 5 suction

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    Re: Casscade Systems

    175 and 5 suction at what point after startup and what temp on the heat xchanger also how much 134a do I put in to start with ?????

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    Re: Casscade Systems

    i think your data tag 1.75 oz. thats about right. the reason they add 134a is to keep the head down. you wanna do this the right way or you wanna just get it working? I grew up working on these guys. do you wanna start over and do it right? i will give you the procedures i have taught to 5 apprentices. While they may seem tedious, I have found after working on thousands of these units, if you want to to the job right (and not have me look down on you as inferior) and have it work, every step is needed.

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    Re: Casscade Systems

    Sure I need all the help I can get I have worked on a few ot these systems so I am a little unsure of myself the only help I have gotten so far is tech support from Thermo Fisher Scientific. My first question early in this thread was can I save a good compressor with polyol ester oil that has moisture in it. According to the factory I cant I should replace the compressor

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    Re: Casscade Systems

    on a first stage with a leak on the acumulator (a common problem as general signal thought it could save money to fabricate thier own acumulators. they learned a lesson)

    1 remove refrigerant
    2 remove acumulator and compressor
    3 remove drier and replace with 1/4 copper of aproxamate size, swedged on both sides
    4 connect valve to high side discharge pipe
    5 connect valve to suction where the acumulator was.
    6 flush with r-11.......i mean rx11?
    7 follow common flush proceedures i.e. with the flow, then back.
    8 insure all flushing fluid is removed by purging with nitro
    9 insulate acumulator leaving room for solder conections
    10 install acumulator and compressor always purging with nitro
    11 dont forget to add your suction access on compressor
    12 add packlees valves for access to your high and low
    13 last welds should be your drier, it starts sucking moisture the sec its open
    14 pressure test 250 psi nitro.. overnight if possibe
    15 purge nitro
    16 change your vac pump oil
    17 install a pretested vacuum manifold with GOOD GASKETS!!
    18 pull vacuum overnight if possible
    19 charge as per data tag
    20 add 404a as needed... it will b
    21 monitor 1, 2, and 3 tcs

  17. #17
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    Re: Casscade Systems

    i want 50 microns from you MR.!!!

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    Re: Casscade Systems

    only one worth anything is earl at thermo. he runs the school. hes a funny guy to. bad teeth though could eat an apple through a fence

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    Re: Casscade Systems

    Sounds good I am starting a compressor change on one Monday I will follow your instructions to the tee when I get to 50 microns how long should my blank off test be

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    Re: Casscade Systems

    how big is your vac pump. model? cfm?

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    Re: Casscade Systems

    i use an extremely sexy welch 1402, but if your using a jb or a yellow jacket, generally they cant pull 50 microns with any leak or moisture. my pump sucks. it really really sux

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    Re: Casscade Systems

    if you are using one of those cheap little cps things. punch yourself.

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    Re: Casscade Systems

    their are different proceedures for different problems but generally its a good idea to flush any time you change a compressor in these things. use your reamer. sand your copper, no tight radius 90s, no dead heads, dont open up your compressor till you are ready to install it, same for your drier. and ALWAYS PERGE WITH NITRO WHEN YOU WELD!!!!!!

  24. #24
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    Re: Casscade Systems

    its a United Refrigeration model GVP 6 CFM

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    Re: Casscade Systems

    I have some welch 1402's in my shop that need some attention they were there when I took over one or two work I will check them with a micron guage

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    Re: Casscade Systems

    what does your vacuum manifold look like? do you use the same manifold for pulling a vacuum? where do you put your micron gauge? SPLAIN!

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    Re: Casscade Systems

    its a yellowjacket with a guage at the top then 2 3/8 fittings a valve 1/4 fitting valve then it connects to the pump I connect my micron guage to the 1/4 inch pump fitting so if needed I can valve off the refer system and check the preformance of the pump

  28. #28
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    Re: Casscade Systems

    I did the compressor and accumulator change this week and flushed the system with RX11. I was amazed at how much crap and moisture that I flushed out. I have another unit to work on that has a restrictiion on the 2nd stage. Im going to flush it and change the oil seperator and drier

  29. #29
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    Re: Casscade Systems

    I ordered the parts to rebuild a welch 1402 that I have in the shop so I will have goood deep vac pump to use and I found a welch 1397 that I will rebuild,,,,,, that one has an evacuation rate of 17 CFM

  30. #30
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    Re: Casscade Systems

    the 1397 has a smaller reservoir so you need to change the oil allot more often. Frank Faulkerson says to use flared copper pipe instead of hoses when pulling a vacuum. I think thats a bit much, i have 3 different vacuum manifolds for different applications. ill take pictures for you, they're difficult to describe. 1sts stage acum leak your gonna have green funk flowin like a freestyle rapper. there is an art to flushing properly. i'll see if i have pictures of the flushing machine i built.

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    Re: Casscade Systems

    I flushed with RX11first and got allot of crap out of the heat xchanger but not much from the condenser then I purged with nitrogen after that I flushed with 134A untill I got pure liquid out. I installed the new compressor and accumulator then I started pulling the vacuum and it pulled down much quicker than before. Anyway Im starting to get the hang of it, you have been very helpful, cant wait to see your vac manifolds

  32. #32
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    Re: Casscade Systems

    My next task is a Revco -80 that has a restriction in the 2nd stage. Im going to pull the oil seperator back flush the system and then replace the oil seperator with a new one pull a good vac recharge and see how it works

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    Re: Casscade Systems

    should flush system,change dyer, oil sep and oil ,, to alkylbenzene,, flush compessor charge oil sep to 600mls and comp to oil removed, pull vacumm to -10 add propane to 0psi and charge to weight system should run down ok if 1st stage ok p.o.e prone to oil logging 1st stage should run in vacuum -5pi unloaded

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