promotion image of download ymail app
Anonymous asked in Home & GardenMaintenance & Repairs · 9 years ago

Central Air blowing humid air?

OK guys and gals I need some help, we have asked many people in the HVAC industry and still have no solution...

We have a 1272 SQ' house with a older A/C system. The unit is blowing the correct temperature, say 15-20 degrees cooler than the return air, but it is really humid.

Some quick background, the unit in located in the crawl space under the house, and the house was built in 1972, single story, no basement, and located in Central Arkansas if that helps any.

What we have done so far...

We change the air filter every 20-30 days so it is clean.

We have checked the drain pan and water is draining correctly.

We have cleaned the coils outside and under the house.

We have verified that the return ducts are connected securely and not leaking any air.

According to our "A/C" guy the freon levels are correct.

We have added insulation to the suction line as there was none.

The house will get to say 72 degrees all day long, but it feels like 82 due to the humidity. The A/C is blowing air at approximately 80-85% humidity and the whole house is about 70% give or take. PLEASE HELP GUYS we are dying here, I hate looking at the thermostat and it saying 70-72, but I am sweating!!

Also we have purchased a dehumidifier, but the air it blows out is very hot and just made things worse.


Not 100% sure on the size of the unit.

I believe it is a split system.

We believe the air handling unit to be pushing 20 years old, and the condenser out back is about 7 years old.

Update 2:

LOFT1009: That sounds like a very intelligent answer, but for a non HVAC technician it very hard to understand. If called a local company to to check that what would I tell them, just print your response and give it to them ? Sorry to be so ignorant, but I am truly lost now.

5 Answers

  • 9 years ago
    Favorite Answer

    There is an issue within the refrigeration circuit. My belief given the indoor coil is clean would be that the low side or evaporator coil has too high of a saturation temperature. Meaning the pressure/temperature of the coil is well above the typically 40F it should be at making it possible to cool the air but not remove the humidity since the coil temp is closer to the dew-point than it should be. Most common things that would cause this would be an either an overcharged unit, bad compressor valves, oversized orfice or txv issues.

    If you have a hermetic compressor the valves are possible, not possible if you have a scroll compressor.

    If the guy added refrigerant, than it could be overcharged, but likely there is another problem going on he was trying to mask, could be a txv. The orfice is used on older systems before txv's came out and the size of the orfice is put in the day its installed, unless a portion of the equipment has been changed recently than this could be ruled out.

    I would be interested to know what the temperature of the suction line is

    - low side pressure

    - high side pressure

    - liquid line temperature

    - outdoor temperature

    - indoor wet/bulb

    - compressor amps w/275psig and compressor RLA

    - type of metering device.

    Get a NATE certified tech, he will know the technical ins and outs, checking external static pressure in ductwork, superheat, subcool and so on, no bother printing this out - he should know all this - we did pass the same test. I suspect the compressor valves are at fault, but for 7 years thats pretty early to go bad, and we'll hope thats not it, and now that I think of your units being installed at different times I wonder if the correct orfice was changed at the indoor unit to match the outdoor one, but the compressor can be tested 3 different ways.

    1- higher than normal suction pressure, lower than normal head pressure

    2 - checking the compressor amperage vs. its RLA while forcing a 275 head

    3 - pumping the unit down and checking for a suction pressure rise

    - Find any ifmoration you can about the outddor unit (service/install, manuals), sometimes the orfice size is listed on it but not always, if the orfice is the case and no literature can be found than the tech is kinda left stuck on hold with technical support for who knows how long with the manufacturer.

    I don't sponser NATE in any way or recieve endorsements from them so to speak, I would just like to see you get someone that can offer a solution vs, a technician giving you the run around - the equipment needs replaced. Sometimes replacement is the route to take - but a solution or fix should also be given.

    • Commenter avatarLogin to reply the answers
  • Boe
    Lv 7
    9 years ago

    Oversized central air conditioner the central air conditioning is an excellent dehumidifier. An oversized central air conditioner, however, has on-cycles that are too short to effectively remove humidity. Also, the cold air may actually increase the relative humidity, making your home colder and clammy.

    You need to find out via a load calculation from your HVAC contractor what size unit your house is suppose to have.

    Now lets say that you do indeed have the correct size unit. I went though this same thing here after according to the home owner 10 contractors came out. They had tried everything possible over a 2 year period. And pretty much gave up. All had there take on the who,what and this is gonna fix it for XYZ. After I verified everything that you had mentioned above and some extra things not listed.

    I determined that the system was in correct order.

    The long and short of this story I installed a crawl space ventilation fan. The crawl humidity was getting sucked into the system. We sealed as best as possible every seam, seal nook and crack we could see. But the air handler would never be "air tight" about a week later after the installation of the crawl space vent fan and with a personal follow up visit. The issue was resolved. You may consider that as a possible source of your added humidity. I cant say that this is the "magic fix" as there could be other factors involved. But if system tonnage is correct, evap coil is correct, air handler CFM meets requirements for condensing unit, supply and return vents are correct. I would take a hard look at the crawl. Hope this help point you in the right direction.

    Source(s): former hvac tech
    • Commenter avatarLogin to reply the answers
  • Marko
    Lv 6
    9 years ago

    Was the humidity high last year, too, or did this just start? Or when the condenser was changed 7 years ago. How long ago was the insulation put on the suction line ?

    edit: Wish I knew the return air temperature AND the suction line pressure. This will give a TD measurement, e.g., 72 degree return air temp and an 84 psig suction line pressure, converted to 50 degrees, will be a 22 degree TD (72 minus 50). A 35 degree TD translates to 50% humidity so a lower TD means higher humidity.

    TD = Temperature Difference.

    • Commenter avatarLogin to reply the answers
  • 9 years ago

    Your AC unit and your dehumidifier are basically similar units, (the AC unit has part of it outside). Both units pass hot moist air over their cooling coils where a) water condenses out and b) the air transfers heat into the coil. For you AC unit the heat is dumped outside, for the dehumidifier it simply dumps the heat out the back of the unit.

    If there is condensation on your AC coils, then that unit may not be able to keep up with the load it needs to handle. The dehumidifier in combo with the AC should work. The dehumidifier would work to take excess moisture out of the air. It will also generate a lot of heat that the AC unit would then need to remove.

    Also check for your insulation and air leakage. A poorly insulated house can substantially increase the load on the AC unit.

    • Commenter avatarLogin to reply the answers
  • How do you think about the answers? You can sign in to vote the answer.
  • 9 years ago

    1st question, what size is your unit? 2nd question, is it a heat pump or a split system? last, how old is the unit?

    • Commenter avatarLogin to reply the answers
Still have questions? Get your answers by asking now.