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high superheat with normal sub cooling

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Old 05-02-2013, 08:53 PM   #1
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high superheat with normal sub cooling

hello to everyone here, im new here and was hoping for a little insight on a few issues I'm having with some trane straight cool split systems. Ive got a trane twe024p130b0 ahu with a trane 2ttb3024a1000ba condenser using r22. 3/8 x 3/4 line set which is probably close to 60 feet long with a vertical lift of around 30-40 foot high to the ahu. about a year ago i replaced the condenser because the old compressor failed. i was performing my yearly pm on this unit when i found it with like 2 degrees of superheat at the condenser with roughly 5-6 degrees of sub cooling. i removed some refrigerant to see if that would help at all with my low superheat but my numbers did not change. So i decided to pump down the unit so that i could remove the txv to replace it and also the fc check valve and while i had it evacuated install a new filter dryer. the unit would not pump down so i just recovered all of the charge. while i had the evaporator out i removed the txv and replaced it and cut out the check valve and did not reinstall it. so i basically removed the bypass since it was a straight ac system. fast forward to starting the system back up after weighing the amount it called for. at first everything started to look good, high superheat in the 40s and low sub cooling in the 1 and 2 range. so i figured good its a little low on refrigerant so i started to add. as i added my superheat began to fall as my sub cooling started to climb but as i got close to my 10 degrees of subcooling the superheat would not get below 23 degrees.subcooling chart says to add 5 psi to allow for the lift so i did. my pressure are suction 52.7, discharge 147.2,
suction line temp 51.8, liquid line temp 67.5, vsat 28.4, lsat 81.5, superheat 23.3, sub cooling 14.0. oat 70, iat 70, supply temp mid 40s, very undersized duct both supply and return, 750 cfm measured with a hot wire anometer on the supply side. what am i missing here? did i mess up by removing the fccv from the evaporator? the new txv was a sporran 2 1/2 ton with a v44 powerhead. any help would be appreciated

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Old 05-04-2013, 08:03 AM   #2
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Re: high superheat with normal sub cooling

Your liquid line being almost 3 degrees colder then the outdoor temp would tend to indicate that there is a restriction in the cabinet of the condenser. Or at least before your temp probe.
How many times must one fix something before it is fixed?
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Old 05-31-2013, 12:50 PM   #3
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Re: high superheat with normal sub cooling

ya I agree your unit is going to be destroyed with all this change. sounds to me like you may have non condensables in the system. try putting a vacuum on the system for along time and install dryers on both lines.. that might help i had a similar problem and that worked for me..

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Old 06-07-2013, 02:33 PM   #4
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Re: high superheat with normal sub cooling

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