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Hi, I'm Tim and I'm an HVAC expert here to assist you with your questions. Please provide all information I request as it makes it more difficult to troubleshoot something when I'm not there onsite. Essentially, you become my eyes and ears. Thanks for the opportunity to help. At the end of our dialog, you will have a chance to rate my service, but please wait until we are finished and you're satisfied you have all the information you need. Please be patient as many times we work with several customers at once.
Low subcooling can be caused by excessively dirty condenser, poor airflow through the condenser, or undercharged.
Make sure TXV is the proper one for unit. Otherwise, low subcooling can be caused by some of the things I mentioned previously.
You should always charge a heat pump system in the cooling mode. I assume you are doing that. It's possible that the reversing valve could be malfunctioning, yes. Remember a slow turning condenser fan and a dirty coil (outdoor) can also cause low subcooling. Have you rinsed out the condenser thoroughly with a stream of pressurized water?
Low subcooling is caused by the refrigerant not giving up it's heat as it passes through the condenser. What could cause this? Dirty condenser coils. A fan that is not working properly, etc.
Also, we should look at other factors. What is the TD (temp difference) across the indoor coil? What kind of pressures do we have? High and low side. And what kind of day is it? Hot, humid? Is the device you're using to measure sub cooling making good contact with the liquid line so we are getting an accurate reading?
Thanks. I have to leave for a bit, but when I return, Ill look at your readings and respond.
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Did you have additional questions? I notice you had not rated question yet.
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Yes, most likely. Also, always install a filter-drier close to the evaporator coil whenever you open a system up.
It should be installed.