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  1. #1
    Join Date
    Jul 2004
    Location
    NJ
    Posts
    1,793

    Unhappy

    How low should a recipricating comp.be able to pull down when suction valve is frontseated?and how fast should the back pressure rise after jumper on lpc is removed to consider the compressor sound?say its a 7.5 HP comp.
    it was part of my previous post but I guess it was boring...

  2. #2
    Frankly, get ahold of the compressor manufacturer's chart for your model unit and use it to determine whether or not your compressor is weak or not.

    I used to go by that suction valve test. But not any more.
    It is just NOT accurate enough against the value of a compressor replacement.

    This is what I would do in your shoes.


  3. #3
    Join Date
    Sep 2002
    Location
    South Dakota
    Posts
    6,579
    Closing the suction service valve to see how low the compressor is capable of pulling down is not a viable test of the compressor and its valves.

    I once saw a six cylinder compressor pass this test yet when the compressor was taken apart it was totally missing its suction and discharge valves from one cylinder. Even with the total bypassing of gas in one cylinder it was able to go deep in a vacuum and pass the test. The test may work for a single cylinder compressor but nothing more.


  4. #4
    Join Date
    Jun 2004
    Location
    Long Island, NY
    Posts
    37
    I once replaced (out of the box,a new comp)on low temp 4 dr reach in refrig w/cond unit on top in a hotel kitchen. Installed new comp and started up unit and it would not pull dn to temp. Chk unit for everthing(restriction,leaks etc) I then frontseated suc serv valve and gauges read 19in Vac(which at the time I thought was good). any way returned back comp to supply house and for another.(at that time if comp was deemed good by MFG I would eat that comp and the new one I was buying)When I installed the new compressor and fronseated suc serv valve the gauges read 26in vac. and the unit pulled down on temp. My ans. to you is that on low temp the comp valves are critical and should pull dn to 26in vac. However that same comp w/19in vac. might have worked well in an A/C unit. Bott line new comp should pull a 26in vac. R12rules reply was correct however MFG comp specs are not on hand most times and are not that easy to obtain while at the job site. Sorry for the ranting Good luck...

  5. #5
    Join Date
    Jun 2004
    Location
    Long Island, NY
    Posts
    37
    More on subject. You have to make sure that the suc/disch serv valves hold tight and do not leak by.(give you a false reading on comp valves). Rotor lock valves are most efficient.

  6. #6
    If your doing business with a supply house which has a fax machine, then you can request the compressor curve chart be faxed over to your work site.

    I used to swear by those valve tests. But not anymore. I had an experience once that taught me the truth.


    I my over twenty years of sniffing freon, I have only replaced one compressor that didnt deserve to be replaced. Only one.
    And this was due to my using that valve test which you spoke of.
    Had I not used that test but goten my hands on the chart .... I would have an unblemished record to this very day.


    Now really ... how hard is it to call the counterman and give him your fax number and unit model/serial numbers?
    And just weigh this against making a serious error in possibly replacing a compressor when in reality, you have a different problem altogether.

    You do the math.
    You make the decision.
    It's you who has to live with the results.

  7. #7
    Join Date
    Jul 2004
    Location
    NJ
    Posts
    1,793
    Originally posted by jackmm1
    More on subject. You have to make sure that the suc/disch serv valves hold tight and do not leak by.(give you a false reading on comp valves). Rotor lock valves are most efficient.
    that was another concern I had.how could I be sure?can I frontseat both valves to see if pressure inside compressor is rising?

  8. #8
    Join Date
    Jun 2004
    Posts
    847
    R12rules. Can you explain further how to use the chart curves to determane if the compressor is bad or not. or give a referance to read about it. thank you

  9. #9
    Join Date
    Jul 2004
    Location
    canada
    Posts
    15
    UP

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