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  1. #1
    Join Date
    Apr 2005
    Location
    Virginia
    Posts
    176
    I have a question on charging a Payne 1.5 ton H.P. with a fixed metering devise with superheat. I followed the charging procedure according to manufactures specs. which are find the wet bulb temp of the air entering evaporator coil which was 72 deg. and outdoor temp which was 85 deg. According to the first chart is stated that I had a superheat temp of 26. So I went on to the second chart provided by manufacture which stated at 26 deg. superheat and the suction pressure of 73 psi the suction line temp should be 61 deg. which i achieved by removing a little freon. Does this sound right. Because I have read many times on this site that the superheat should be between 10-20. Indoor temp was 84 and I ended up with a delta t of 16 deg. What doesn,t make since to me is the superheat chart went from 0 to 40 deg superheat.

  2. #2
    Join Date
    May 2000
    Location
    Indianapolis, IN, USA
    Posts
    34,179
    The superheat should be what the mfr says. Hot in cool out you'll have a 30-40 degree superheat. Cool in hot out you'll have almost no superheat. The joys of a piston. Superheat is based on inside load and outdoor temp.

  3. #3
    Join Date
    Aug 2003
    Location
    Fort Worth, TX
    Posts
    11,346
    Bald One is right on. The 10-20 degree superheat you referred to is for TXV systems.

    Hot ambient outdoors and cool temps across coil indoors will result in low superheat with a piston due to both reduced heat load and increased mass flow rate through evap due to higher head pressure from higher outdoor ambient.

    Have I mentioned that I think pistons are crap?
    • Electricity makes refrigeration happen.
    • Refrigeration makes the HVAC psychrometric process happen.
    • HVAC pyschrometrics is what makes indoor human comfort happen...IF the ducts AND the building envelope cooperate.


    A building is NOT beautiful unless it is also comfortable.

  4. #4
    Join Date
    Sep 2003
    Posts
    1,311
    72 wetbulb indside? Did you perhaps measure dry bulb?

  5. #5
    Join Date
    Sep 2001
    Location
    Vancouver Canada
    Posts
    996
    sadlier


    He mentioned 72 degrees wetbulb, 84 degrees dry bulb indoor temp.
    "Go big or Go Home"

  6. #6
    Join Date
    Jul 2004
    Location
    Illinois
    Posts
    8

    Hmm

    Your #'s don't add up. You said you have a 84degF indoor drybulb and a 85deg outdoor drybulb and a 16deg delta T. I'm confused!Are you sure these are the right #'s?

  7. #7
    Join Date
    Apr 2005
    Location
    Virginia
    Posts
    176
    Originally posted by banshee
    Your #'s don't add up. You said you have a 84degF indoor drybulb and a 85deg outdoor drybulb and a 16deg delta T. I'm confused!Are you sure these are the right #'s?

    I am pretty sure my numbers are correct, I will have have to back over service report. And why don't the numbers add up? I will post the results again when I have the report in front of me. I wish my memory was alot better I have that CRS disease( Can't Remember SH**) Its terrible I know!

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