my first thought is you need another opinion and another HVAC guy.

pls provide more details if you expect any knowledgeable reply. Provide complete model numbers for the bedroom system, both inside and outside units. It is quite rare for a bedroom to have its own separate system from the remaining living area of a home. Why? I would take some humidity readings yourself for the bedroom. Note outside temperature and outside humidity over the course of the day. Generally, I think it is unreasonable to expect good humidity control with such a high temp setting. I will assume your system is working correctly.

IMO

well i dont see model numbers. this was a home we custom built in 1991 and the master bedroom wing has its own AC system. I am sitting in here now thermostat is on 79and i am freezing! outside temp now is 82. as the day goes on or if im out and come back in the room has a humid dampness to it. (i have investigated any other reasonable type of water source other than the AC) other rooms in the house do not have this problem. (concrete slab foundation) should i be looking at something other than the HVAC system to dry the air? will a freestanding air purifier accomplish that?

If you have a Trane split system serving only one bedroom that its most likely WAY, WAY, WAY, oversized. That would explain your humidity problem, as the system is so big it drops the temperature before it has time to dehumidify the air. No matter what temperature you have it set at, it will always be muggy, damp and musty!

You could add ductwork to the rest of the rooms so that the AC cools the entire house - that may address the oversizing and humidity issue.

Here we go with over sizing rhetoric without actually knowing anything about the structure or the actual size of equipment let alone much anything else other than it was built in 1991. I own a magic 8 ball and even he can't predict things like this. How over sized is way, way, way? (remove the whole unit you don't need it -over sized?)

While Florida is not my market it is very similar in relation to heat and humidity complex.

Realize humidity and temperature are independent from one another. If you are this sensitive to temperature you will not cure the humidity aspect of your climate with air conditioning equipment alone. You would likely have to spend more for a system attached dehumidifier that would run to reduce humidity without effecting temperature. Just realize this can add 30 to 50 a month to your light bill in addition to whatever cooling costs you have. It wouldn't hurt to investigate the humidity part of the equation and find what the differences are inside the home in various places. This information may help you find a problem, or it may not. Also use a separate temperature reading at the thermostat to determine the thermostat is displaying accurate temperature. You know to find out that 79 degrees is actually 79 degrees.

With that said: A master suite in many homes can be upwards of 1000 square feet or more alone once you figure closet and master bath. Add in high ceilings (12 foot typically) and possible large windows facing east or west all of which add to heat load calculation. This room could easily require around 2 tons of cooling or more for a Circa 1991 home. (IE: not all master suites are built identical to one another... if you think this you need to get out more.)

ANY (properly sized) air conditioner is way, way, way, way over sized in operating conditions of 82 degree OAT (depending on design characteristics and location). It's all based on loads. If you decrease the load, the capacity of the system goes up. What is a load? -HEAT- The lack thereof increases capacity.

Given the amount of info the OP has supplied that's about as far as I will go here.

Why mess with all that, get a portable dehumidifer and an air purifier, or a combo unit, then let the AC run as needed for cooling.

Unless you want to spend a LOT of money on an HVAC system that can do everything for you, and get it working correctly, and keep it working correctly.

Good luck.

Because a portable dehumidifier will require you to empty the condensate water. It will be unsightly in a room you tend to want to look nice and have a pleasant feeling when you walk in there.

In a high humid room this may equate to having to empty the water a couple times a day.

Then on top of that make sure you get sizing right of the portable, otherwise it won't be able to keep up.

Oh, you're going to mess with something... no way around that.

Can you post the approximate area of the master bedroom area? Also if is a single story, if you know anything about insulation values, number of windows, and direction the windows face.

Take a closer look at the condenser sitting outside. Look carefully at the sides for a model name plate. It should be there but after 26 years it might not be legible. Take a picture and post it. Maybe it can be deciphered.

I don't know how much longer your HVAC guy expects your 26 year AC to last in humid Florida. It may be possible to install a 1.5 ton condenser, or a 2 ton 2-stage condenser with a variable speed air handler. It should improve the humidity control. Technology has improved in the past 26 years. But there may be a limitation in your situation.

If you install a dehumidifier you could buy one with a condensate pump and not have to deal emptying the reservoir each day.

If you are cold,why is the ac on when outdoor temp is 82*F? I'm not being sarcastic (there's already been enough of that) but you should see your doctor. Noone should be freezing at 79*F,regardless of humidity. You might have a medical condition. At any rate,you're obviously not getting much help on the net,

Klem1,

I think there is probably a reasonable explanation that could simply be due to how the system is designed / installed in the home.

The thermostat may be an analog old mercury style thermostat in which it is quite easy for these to be off temperature by 10 degrees... meaning the temp in the room is actually 69 instead of 79.

If it is 69 in the room, the air coming from the vent could easily be 49. If the air is being blown directly on to the OP in the room, this would feel really cold.

Because this system takes care of master bedroom only, the duct runs are probably short and unit likely sits over head.

Now as to why there is an abundance of humidity at this possible scenario mentioned above your guess is as good as mine. (Even with the powers of the Magic 8 ball)

can you please help with this. we decided the best thing to do is hook into the main HVAC for the living areas, Remove the bedroom HVAC all together. then replace the main HVAC unit with a state of the art 3 stage system (he uses american standard) Here is my question. Today in Florida it is 49 degrees! freezing for here. humidity in the house is like 20% but for some reason in my bedroom its like 60% (no ac running cuz its cold) Same floor, same type doors and windows, adjacent to living space, My room always feels damp. smells like mildew. Two mold companies have come and tested with meters to look for moisture in the floor or behind the walls and found none. I am convinced there is some sort of dampness present in this room (no carpets or drapes ) only tile, wood furniture. not much clutter, closets have been emptied into another room in prep for remediation, new roof, ducts have been cleaned, attic crawl space has been checked. HVAC unit is not dripping or clogged(that i can see, was just serviced and uv light added) the HVAC plenum is dry (although there is mold on the drywall in there) waiting for remdeation. My question is where else can i look for a moisture source? does mildew (smelling like damp towels that have sat for a while) have to mean there is a sitting water source somewhere? any other ideas. isnt it logical that if its a freezing day here i shouldnt need AC to draw humidity out of my room today?!

Today in Florida it is 49 degrees! freezing for here. humidity in the house is like 20% but for some reason in my bedroom its like 60% (no ac running cuz its cold) .

If this is the case then it sounds like you have water accumulating in the vicinity of the bedroom. Do you have a crawl space, a basement or a slab? A mold remediation company should first identify where the damp is getting into the house. If they don't, find another company.

Somewhat dated and somewhat slanted to Northeast US climate, but useful"

My House is Killing Me" by Jeffry C. May.

Humidity control is greatly improved in modern systems with variable speed compressors and variable speed blowers, but you will always have high humidity periods when little or no heating or cooling is needed. To eliminate high humidity totally you need a dehumidifier of some sort, compressor-refrigerant driven or desiccant wheel.

Look at BuildingScience.com (for updates to below) and the Florida land grant university extension office or other states' with similar climate land grant universities. Here are some somewhat dated articles from Building Science Corporation:

Supplemental

Dehumidification

in Warm-Humid Climates

Building America Report - 1310

July 2013

Armin Rudd

---

Conditioning Air in the

Humid South—Creating

Comfort and Controlling

Cost

Research Report - 0214

November-2002

Building Science Corporation

Abstract:

thanks

Jennlehr,

Does this particular room have a bathroom close by?

How many windows?

When you notice this problem the most was it after a recent rain outside?

What exterior things are nearby this room? (a pool or what?) Same thing indoors, what is near this room indoors and are you sure the problem is only this room.

The problem with dropping this down to one system for the whole house is that it probably won't fix this problem and you will have less control over the system in regards to temperature control of this room / and or other rooms of the house.

If there is no pool outside, no recent rain... as a test stop using the master bathroom for a week. shut off all water going to that bathroom. You will need to monitor humidity levels before and after this test, because you will want to know if something changes.

thats also a good idea. yes there is a pool right outside. yes it did rain recently, but if this moisture is coming up via the concrete slab, then im fit to be tied. cuz theres not much i can do about it, short of demolishing the entire room! im going to try the bathroom shut off idea. and we will install a separate dehumidifier in this room going forward.

Yes, newer systems are better at humidity control. You will still have days when little cooling or heat is required that will be outside your desired humidity level. Mechanical cooling removes water from the air. Heating decreases relative humidity by increasing the carrying capacity of the air. If neither is running, dedicated dehumidification is the only way to hit the mark all the time. Somewhat ironically, more efficient home envelopes, insulation and sealing, contribute to the problem by decreasing the need to heat and cool.

How is your space heated, gas furnace in the same systems that cool?

Here is another hypothesis for a cause for local moisture problem in that room. Pressure imbalance due to leaking ducts, or something in the system design may be pulling outside air, a lot of it, into the room. The pressure imbalance could be caused by the bedroom system or the main system.

yes there is a pool right outside.

Ah, ha. I take it the pool is fairly close to this problem room?

How about laundry room is it anywhere near this room?

If that's the case about the pool, it could be infiltration problem and 'maybe' nothing to do with anything inside the home.

You can still do the bathroom shut off idea just to see if it makes any difference and to eliminate things.

If the bathroom shut off idea fails to produce any results, I think you should look out door infiltration into this room. Basically what happens via infiltration is that certain rooms of the house go under negative pressure. When that happens air is brought in thru any crack or crevice. If the crack or crevice happens to be outdoors then outdoor air is brought in.

In some cases the crack or crevice may be door, light socket, lighting fixture etc. Overtime if you haven't painted it becomes apparent by dust or dirt patterns near the crack or crevice. However, if this occurs from under a base board at the bottom of the room this dirt can be disguised with normal floor dirt.

Infiltration such as this can be a difficult situation to correct. Sometimes just how you operate not to mention how your HVAC system is designed can effect things to one degree or another.

When you heat or cool this room do you keep the door to this room open or closed?

Is there an air return with a filter in this room?