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txv too small

I was working on a carrier water source heat pump today (r410a) m#50 hq installed in april 2013.there was a certified air balance done on the unit, and airflow does not appear to be an issue.the problem is both circuits (6 ton two stage unit) are running with low suction pressure (95-100 psi) to the point where the outlet of the txv starts to ice up and the unit goes out on freeze protection. this occurs on both circuits. the charge has been removed and weighed back in to what is on the nameplate. even though this is a six ton unit with two isolated three ton circuits, the txvs are only rated at two tons each. does anyone else find this odd that you would have a six ton unit with txvs only capable of supplying four tons of refrigeration across the evaporator coil. both txvs seemed to be maintaining a good superheat (12-15 degrees) in the evaporator, it just seems that the evaporator is being starved of refrigerant, and the txvs cannot open any further  


  • TechmanTechman Member Posts: 2,144
    edited August 2013

    What # are on the TXV, what brand ? Did Carrier verify the TXV #'s ? Is it a "balanced port" TXV ? What was the hiside press ? If that's low it makes the low side lower.
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