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  1. #1
    Join Date
    Jan 2005
    Posts
    84
    I just had a txv installed on one of my systems. It is a Sporlan with the following info on it:CBBIVE-3 84.5 1906
    EA36YD037. It was installed on an existing 4 ton rated Allstyle coil. The condenser unit is a new Carrier 24ABR342. After 4 days of operation system is cooling the same as before the txv and daily run times are within 1/2 hr of each other. What I have noticed is that my kw usage is up 15-20%. Nothing else has changed in my home to explain this increase. The weather here in DFW has been very consistent for the last month which corresponds to a kw usage that has not varied by more than 10/day. Now its approx. 20 kw higher than before the txv. Could this txv be too small thus causing a greater load on compressor? I did ask the tech about the 11 degree subcooling required (which is stamped on the side of the condenser) and he said once he charged the system back up it would work correctly and that measuring it was unnecessary. As I watched him charge the system I noticed the right hand gauge on his set didn't work. He commented that he didn't need that one to charge the system. I asked about the left one being pegged out and he said that was normal. Ok, I'm not a tech but I thought the gauges were there to determing proper pressures, etc. Any ideas? Thanks.

  2. #2
    Join Date
    Feb 2004
    Location
    Maine
    Posts
    483
    I would ask how the unit was charged. Sounds like he just used low side pressure to charge which is not good, but I wasn't there so I can't tell you how he charged the unit. TXV systems are charged by measuring subcooling.

  3. #3
    Join Date
    Jan 2005
    Posts
    84
    2nd tech came out to check system. Amp clamp showed fan drawing rated rla and compressor drawing a little under. ODT was 102, indoor 76 at 40% rh. Low side was 79 and hi 250#. He stated that based on the numbers txv appears to be working just fine. He stated that if it were undersized the pressures would be higher. I asked about subcooling and he didn't think that was necessary based on what he had already observed. He couldn't explain the additional kw usage, but recommended getting another opinion if it persists. He did suggest replacing coil. Well, according to Allstyle, equipping my 6 year old coil with a txv coupled to the condenser I now have should result in a 13 seer efficiency. Comments?

  4. #4
    Join Date
    Dec 2002
    Location
    Houston,Tx.
    Posts
    15,826
    Originally posted by tmoss
    Comments?
    Yes did both of them arive in horse drawn buggies?
    __________________________________________________ _______________________
    “Experience is a hard teacher because she gives the test first, the lesson afterwards". - Vernon Law

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  5. #5
    Join Date
    Feb 2004
    Location
    Maine
    Posts
    483
    Originally posted by tmoss
    2nd tech came out to check system. Amp clamp showed fan drawing rated rla and compressor drawing a little under. ODT was 102, indoor 76 at 40% rh. Low side was 79 and hi 250#. He stated that based on the numbers txv appears to be working just fine. He stated that if it were undersized the pressures would be higher. I asked about subcooling and he didn't think that was necessary based on what he had already observed. He couldn't explain the additional kw usage, but recommended getting another opinion if it persists. He did suggest replacing coil. Well, according to Allstyle, equipping my 6 year old coil with a txv coupled to the condenser I now have should result in a 13 seer efficiency. Comments?
    Can't charge by pressures alone, systems using a TXV are charged by subcooling. Let me explain why. The job of the TXV is to vary the amount of refrigerant into the evaporator to match the heat load on the evap, this keeps the superheat constant and allows you to use almost the entire evap for cooling under varying load conditions. Subcooling tells us how much liquid refrigerant is getting backed up into the condenser. If the system is overcharged more liquid refrigerant remains in the condenser, this effectivly reduces the coil area that is used to cool the hot high pressure gas in to a cooler high pressure liquid. Subcooling the liquid beyond what the manufacturer states is the equivalent of blocking a portion of the condenser off. The unit must run longer to extract the same amount of heat and thus your electric bill goes up. An a/c units effieciency is more affected by an overcharge than an undercharge. Your unit could be overcharged or undercharged, as either will affect effieciency. Subcooling is a simple measurement that takes only a few moments of time. Basically subcooling is the temp of the liquid below it's condensation temp, water that exists as a liquid below 212 degrees is actually a subcooled liquid, so if you have a container of water that is 100 degrees F there is 112 degrees F of subcooling. Have a tech come out and demand that the unit be charged to the subcooling listed on the unit, if the tech doesn't know how, get another out there that does. Hope this helps.

  6. #6
    Join Date
    May 2006
    Posts
    312

  7. #7
    Join Date
    Jul 2005
    Posts
    717
    [QUOTE]Originally posted by mrbillpro
    [Yes did both of them arive in horse drawn buggies?
    ----------------------------------------------------
    aw, com'on, everyone knows that HORSES can't DRAW.

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