Heating, Air Conditioning, Fridge, HVAC/Residential AC RH


Hi Joe,

I've read that, generally, the AC air speed should be on high and the heat air speed somewhat lower.  However, I've also read that it is common practice to reduce air speed to extract more moisture because the "newer, more energy efficient AC units" generally extract less moisture to begin with.

Question 1. I've found that for my AC to extract the most moisture, and for the evap coil to get to the low end of its cold range, I have to put the blower on the lowest of 4 speeds.  Is this "normal"?....Is it true that newer AC units inherently extract less moisture by their more energy efficient design and that the only way to get them to extract more moisture is to lower the air speed?

Question 2.  Assuming the AC is functioning as well as it ever will, what can be done to extract more moisture; e.g. smaller/bigger AC,  differently designed AC....the reason I ask is because, even though my AC functions within normal parameters with the air speed on the lowest setting, the RH in the house in the summer still stays between 60-65 with the AC set on 70-74.  I assume this is because the house is on a slab and the air vents are under the slab.

Question 3.  What difference between outside and inside RH can be expected of any current residential central AC in summer when outside temps/RH is around 80-90 deg F and outside RH is 80-90. (I know the temp difference is around 20 deg, but not sure about RH.)

Thanks for your help!


You probably can get a better answer than I can give by google your questions. Smaller would be better to remove moisture than larger, as run time has a lot to do with it. The slower the fan speed would pick up more moisture across the indoor coil

Heating, Air Conditioning, Fridge, HVAC

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40+ years diversified experience.An HVAC/Refrigeration Self Employed Contractor since 1986. NATE Certifield. Answer questions pertaining to Residential and Commercial Air Conditioning , Warm Air Heating, Heat Pump systems.Mechanical and Electrical troubleshooting of these systems.Be as detailed as possible when describing problem.Packaged unit or split systems.No appliance questions.


Installation and Troubleshooting, Mechanical and Electrical, in following areas, Refrigeration ( Walk In and Reach In Coolers and Freezers ) Commercial Roof Top and Packaged Heating/Cooling ( Natural Gas,Propane, Electric, and Heat Pumps ) Computer Room Air Conditoning Systems,Commercial Residential Packaged and Split Systems Air Conditoning and Heat Pumps.Warm Air Oil , Natural and Propane Gas Heating systems.

Graduated from Private Technical School in 1975. An HVAC/Refrigeration Contractor . Have Unlimited Heating/Piping and Cooling Contractor License.Limited Sheetmetal Contractors License.NATE Certifield. York Certifield Master Heat Pump Technician 1986. Served 33 years combination Active Duty Air Force , Air Force Reserves and Air National Guard in the HVAC/Refrigeration Shop/Mechanical Shop. Troubleshooting/Installing HVAC/Refrigeration Equiptment Worldwide. Retiring in 2003 as a Senior NCO ,and a Mechanical Superintendent.

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