Results 1 to 10 of 10
  1. #1
    Join Date
    Apr 2005
    Location
    Australia : Queensland
    Posts
    1,845
    Post Likes

    Confused Pressure change.

    Small CoolRoom at a gas station ,, -5SST ,, iced up coil ,,, deiced coil & was testing thermostat & pumpdown function. Thermostat deenergises LLSV & unit should pump down ,,, sat on the roof for 5 mins waiting for it pump down but my pressure stayed at -5 & the thing wouldn't cutout.

    Light showers came through & when I could get back on the roof it pumped down this time ,,,,,,, any thoughts ??? Intermittent fault with the LLSV slide grabbing ?
    The primary function of the design engineer is to make things difficult for the fabricator and impossible for the serviceman.

  2. #2
    Join Date
    Aug 2002
    Location
    Southold, NY
    Posts
    26,024
    Post Likes
    Low pressure control not opening?


    When in doubt close the suction. If it shuts off open it and close the receiver and check.

  3. #3
    Join Date
    Apr 2005
    Location
    Australia : Queensland
    Posts
    1,845
    Post Likes
    Thread Starter
    Quote Originally Posted by pecmsg View Post
    Low pressure control not opening?


    When in doubt close the suction. If it shuts off open it and close the receiver and check.
    Closed suction & system did cut out LP ,, was low but I did fine tune it.

    I closed the liquid line to the Evap & the SST remained at -5SST R404 & never budged.
    The primary function of the design engineer is to make things difficult for the fabricator and impossible for the serviceman.

  4. #4
    Join Date
    Mar 2015
    Location
    Medford, N.Y.
    Posts
    6,189
    Post Likes
    What was hi side press during the pumpdown?

  5. #5
    Join Date
    Apr 2005
    Location
    Australia : Queensland
    Posts
    1,845
    Post Likes
    Thread Starter
    Quote Originally Posted by TechmanTerry View Post
    What was hi side press during the pumpdown?

    400psi with a piperun no longer than 20mtrs.
    The primary function of the design engineer is to make things difficult for the fabricator and impossible for the serviceman.

  6. #6
    Join Date
    Jun 2013
    Location
    N. Canada
    Posts
    874
    Post Likes
    With 28/400 maybe the showers cooled that 60c (140f ) condenser?



    Isn't -5 (5"hg) pumped down enough? Sure would be with a scroll.
    Adjust the LPS.

    good luck

  7. #7
    Join Date
    Mar 2015
    Location
    Medford, N.Y.
    Posts
    6,189
    Post Likes
    400 psi on a cool day? Not enough room in receiver for a pumpdown?Overcharge?

  8. Likes tmt, trippintl0 liked this post.
  9. #8
    Join Date
    Apr 2005
    Location
    Australia : Queensland
    Posts
    1,845
    Post Likes
    Thread Starter
    Quote Originally Posted by TechmanTerry View Post
    400 psi on a cool day? Not enough room in receiver for a pumpdown?Overcharge?
    The -5 is degrees Celsius while system is chilling. This is the figure also after closing liquid line and did not change.

    Was thinking the same thing Terry , but after switching unit off for some time to deice coil & set correct superheat the system finally pumped down ,,,, although the LP was set low I adjusted.

    What I'm trying to get my head around is why it didn't pump down when I was at site first ,,, then after switching off to to the above repairs & a scud shower passing over ,,,,the system finally plays the game and pumps down.
    The primary function of the design engineer is to make things difficult for the fabricator and impossible for the serviceman.

  10. #9
    Join Date
    Mar 2015
    Location
    Medford, N.Y.
    Posts
    6,189
    Post Likes
    On a proper sized cond coil/receiver the head press should go down just a little towards the end of the pumpdown. 400 psi is not right.

  11. #10
    Join Date
    Apr 2005
    Location
    Australia : Queensland
    Posts
    1,845
    Post Likes
    Thread Starter
    Quote Originally Posted by TechmanTerry View Post
    On a proper sized cond coil/receiver the head press should go down just a little towards the end of the pumpdown. 400 psi is not right.
    You are right.

    I was leaning towards some obstruction inside the solenoid valve body that was preventing it from seating fully (but then my LP still should drop some to notice the restriction) but after shutting unit off this obstruction shifted ,,,, all is running fine now after some SH & defrost adjustments.
    The primary function of the design engineer is to make things difficult for the fabricator and impossible for the serviceman.

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •