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Tim H.
Tim H., HVAC Professional
Category: HVAC
Satisfied Customers: 3971
Experience:  Experienced in all aspects of HVAC, both residential and commercial.
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I have a carrier 410A heat pump model 25hcb324a300, equipped

Customer Question

I have a carrier 410A heat pump model 25hcb324a300, equipped with a txv at the evaporator coil and im charging by subcooling by liquid only and my recommeded subcooling for the unit is 12. As I add refrigerant to the unit my sibcooling stays at 3 to 4 degrees no matter how much refrigerant i out in it. I tried changing out the txv at the evaporator but still the same. Please help.
Submitted: 11 months ago.
Category: HVAC
Expert:  Tim H. replied 11 months ago.

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.

Customer: replied 11 months ago.
Well from the looks of things the condenser coil looks ok. And my head pressure was around 265 normallybits around 350 on a normal hot day. My suction pressure was around 107 kind of high, and no matter how much freon I add my subcooling does not change. I havn't tried to clean the coils but im certain there may be something s else. Perhaps the outdoor txv thats build into the condenser coil. Im at a 234 unit apartment building and I have two unit doing the same exact thing. I service manybof these units already but for some reason i cant get pass this issue.
Expert:  Tim H. replied 11 months ago.

Make sure TXV is the proper one for unit. Otherwise, low subcooling can be caused by some of the things I mentioned previously.

Customer: replied 11 months ago.
I replaced the indoor txv with the exact same txv and still the same issue. Could it be the outdoor txv be the problem. Also just a reminder my subcooling does not goes pass 4 no matter how much freon I add. If it was a dirty coil would my subcooling at least move pass 4 after i add the freon. Im still stuck on the outdoor txv and how it functions. Could the reversing valve be partially sticking.
Expert:  Tim H. replied 11 months ago.

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?

Customer: replied 11 months ago.
No im doing it in a few. Just dont get why my subcooling stays the same
Expert:  Tim H. replied 11 months ago.

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.

Customer: replied 11 months ago.
Ok now i get it
Expert:  Tim H. replied 11 months ago.

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?

Customer: replied 11 months ago.
Ok
Expert:  Tim H. replied 11 months ago.

Thanks. I have to leave for a bit, but when I return, Ill look at your readings and respond.

Customer: replied 11 months ago.
I just be damn. I blew the coils out with the hose and my subcooling is now rising.
Expert:  Tim H. replied 10 months ago.

Great! Sounds like we're on the right track! Let me know if you have additional questions. Otherwise, good luck! Thanks for using Just Answer and please don't forget to rate my service as that's how experts get paid (thanks in advance for any bonus left). Otherwise experts work at their own time and expense. Even though the Just Answer site has your money on deposit, it does not get transferred to me until you (positively) rate my service. Feel free to post back with any more questions. Remember, you can rate question at any point and still ask more questions (related to the same thing) later on. Experts prefer if you rate question at the end of our first chat.

Expert:  Tim H. replied 10 months ago.

Did you have additional questions? I notice you had not rated question yet.

Expert:  Tim H. replied 10 months ago.

Please understand, even though the Just Answer site has a deposit from you, money is not credited to your expert until you (positively) rate the question. Thank you!

Customer: replied 10 months ago.
Well i still having trouble getting subcooling. But i think i may be on to something. Im in a 12 story building, and all my lower units are having subcooling problems. I evacuated the system and out the vacuum on it for a couple of hours. Charged the and still having trouble getting subcooling. But I notice it fluctuate alot meaning there still impurites in my in system. All units are roof top units and and the line set rins 12 stories long down to the first floor. My vacuum pump is only 1 stage and i believe this may be my issue. Meaning I will need a 2 stage pump.
Expert:  Tim H. replied 10 months ago.

Yes, most likely. Also, always install a filter-drier close to the evaporator coil whenever you open a system up.

Customer: replied 10 months ago.
Well I never did install a filter drier. I know inhave one old one on the liquid line.
Expert:  Tim H. replied 10 months ago.

It should be installed.

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