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Phil
Phil, Mechanical Engineer
Category: HVAC
Satisfied Customers: 7737
Experience:  Retired HVAC/ Electrical & Boiler contractor. Industrial
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I have a new (June 30, 2016) Carrier 24VNA9 compressor;

Customer Question

I have a new (June 30, 2016) Carrier 24VNA9 compressor; FE4ANB air handler; and SYSTXCCITC01-A thermostat.
With cooling temp set at 75/76/ or 77% and the 3 degree button off, the system brings the air temp to the correct level but will not take the relative humidity below 60% (typically 64-68% range throughout the day).
Dealer has been out twice: (1st) system was over-charged and removed some Puron; (2nd) system had erratic pressures; air in line sets; cleared and re-pressurized. Now coming out again to replace the TXV valve.
What do YOU think is going on? What fixes would YOU recommend?
Terry King at(###) ###-####
Submitted: 5 months ago.
Category: HVAC
Expert:  HVAC Guru replied 5 months ago.

Hello and thanks for using this service! If you are a JA Member I would like to personally thank you and welcome you back! I am HVAC Guru an extremely experienced tech on the site and I try to get to as many customers as I can. NOTE it takes time for me to type research and add links so please wait for me to respond back I can only do this so fast. Secondly, I do not know your skill level so please try and let me know if I am going beyond your knowledge or comfort zone thanks! I strive for a 5 star rating from everyone especially our JA members.

How big is the house?

Customer: replied 5 months ago.
1750 sq ft under air.
Expert:  Phil replied 5 months ago.

Hello again, I still need the full model number of the outside unit, that will tell me its cooling capacity.

Here is a list of things that will cause poor humidity control,

1. a slight over charge of refrigerant (even just 2 or 3 ounces)

2. Cooling system is too large for the home, and so comes on and cools

the house, and goes off before it has time to reduce the humidity.

In your case a system that cycles more than twice an hour on a day

over 98F outside would be slightly oversized, and if it cycles 4 or 5

times an hour it would be grossly oversized.

Those are the two most common errors... the fact that the installer has recommended replacing the thermostatic expansion valve is a red flag, along with other factors... nothing related to the expansion valve will cause these humidity control issues.

We can go from here if you wish

Expert:  Phil replied 5 months ago.

http://http://screencast.com/t/z6HXLjEP

I still need the full model number, notice it circled in red...thats from the Carrier manual and just an example.

The region of the country you are in is also relevant, humid areas such as the gulf coast etc need special component sizing...air flow settings are crucial.

Customer: replied 5 months ago.
The compressor unit is 4-ton: Carrier 24VNA9 48A003 and it is the 5-stage system. So it should be able to run at the lower/slower stages to take longer to cool and in turn allow it to take more humidity out of the air.At the last dealer "fix," he said the system should be able to take the RH down to the mid-50% range even with the temp setting at 77 -78 degrees.
Customer: replied 5 months ago.
I am in a high-rise right on the Gulf of Mexico.Are you referring to optional airflow settings in the air handler, or via the thermostat, or what.By component sizing, do you mean 3 or 4 or 5 ton, or components within the air handler?
Customer: replied 5 months ago.
Phil: note also that my neighbor one floor below me has the same size apartment--1750 sq ft--and an identical system to mine. He has no problem with getting RHs in the low to mid-50% range.
Customer: replied 5 months ago.
Phil: I have answered your questions and provided some additional information and questions as well.
You sent me two responses, but no additional information was included in your responses.Something is wrong!
Expert:  Phil replied 5 months ago.

Hello, lunch is whats wrong, I went to lunch

Expert:  Phil replied 5 months ago.

When I am not at lunch, or dinner etc, I am handling several questions at a time and doing the needed research and typing...so there are these delays from time to time

Expert:  Phil replied 5 months ago.

I had included the following my second response.

Had you seen it?

Here it is again

Here is a list of things that will cause poor humidity control,

1. a slight over charge of refrigerant (even just 2 or 3 ounces)

2. Cooling system is too large for the home, and so comes on and cools

the house, and goes off before it has time to reduce the humidity.

In your case a system that cycles more than twice an hour on a day

over 98F outside would be slightly oversized, and if it cycles 4 or 5

times an hour it would be grossly oversized.

Those are the two most common errors... the fact that the installer has recommended replacing the thermostatic expansion valve is a red flag, along with other factors... nothing related to the expansion valve will cause these humidity control issues.

Expert:  Phil replied 5 months ago.

Thanks for the full model number, a 4 ton system was installed in your space, that would normally be considered oversized and would lead to humidity control problems, except for the fact that it is a *variable speed syst.. that is tunable for less air flow at the unit itself to achieve much better dehumidification.

If you can take the temperature of the air at the return air grill, then use the same thermometer to take the temperature 4 inches inside the closest supply air grill, using the same thermometer I can assess those air flow issues. A few tests over an hour or so and only when the outside unit is running will work.

Beyond that, it is also possible that the system might have a few ounces too much refrigerant in it... if you can feel the largest diameter copper tube connected to the outside unit and tell me if it is sweating or not, and if any part of the compressor inside (seen though the fan on top) is sweating, that will help a lot.

Then if you can tell me about how many times an hour the unit outside is cycling per hour and what the outside air temperature is I can determine if it is cycling OFF when it should just be unloading (as you mentioned).

We can go from there.

(a bit about me. I am 75 years old, and still active in the business, the first 40 years running my own operations, and the last 20 years consulting nationally (and some work for Daikin Kogyo in japan). I have a degree in Mechanical Engineering Technology.)

Expert:  Phil replied 4 months ago.

Hello again, I just got notice that you posted, but no text showed up,

Can you repost your response please?

So far it looks like your 4 ton unit is about 20% over sized for the load. That will cause humidity control issues.