• 713 861 1977
  • YouTube
  • Facebook
  • RSS

Ask the Experts

Read More

Central City Air BBB Business Review
EnergyStar EnergyStar Angie's List

Have a Question? Ask Dave

As long as Central City Air has had a website, we have had our "Ask Dave" page. It has always been a place where our customers and visitors could ask David Debien questions about their air conditioning and heating systems. Even though David has passed, we still offer our website visitors the same expertise and technical answers to all of their questions. We have a team of seasoned professionals on hand to answer any question you may have.



Dirty Sock

Posted on 04.04.2016

I bought my home in the Stone Oak area of San Antonio, brand new, on September 21, 2007. It has no heat pump but gas heat and air conditioning. Since the summer of '08, I have been experiencing a horrible odor, like living in a musty tent, coming from the air ducts as the a/c runs. Doesn't occur in winter with heat.

The A/C company that installed the system for the builder has been out several times, checked the ducts. They think that the system turning on and off, wet then drying, has something to do with causing the odor. The cleaned the coil, want me to run my a/c at 74 degrees to prevent it from turning on & off frequently, and most recently put an ozonator in the system. . The ozonator worked a litte, but a faint odor still exists, sometimes more than others, but better than before the device was put in the system.

The a/c company is ready to sell me a Guardian Air Cleaner System for better than $1200. Before spending this small fortune, I reseached Dirty Sock Syndrome on Google. Sounds like a coated coil is a better bet. Even though I don't have a heat pump, is DSS the problem? Either way, what should I do at this point?


From your account of things it seems that you may have what the industry nicknamed "dirty sock syndrome". When you go from the heat side to the cool side it is quite noticeable and every year it gets worse and lasts longer before the coils wash themselves off. We experimented with all the different ways to handle this problem and finally landed on a new coated coil. Reusing a contaminated coil to coat will not work, best to get a new coil and have it coated. Once this condition appears it seems to remain in the home and it reappears, coating the coil before installing has made a difference for us and works well. The coating we use is Bronz-Glow out of Florida.

As far as the advice you were given to run your air conditioner that cold, you will just be cold and may have some sweating windows but you will still have the dirty sock syndrome.

Return Air size and type

Posted on 07.30.2014

Question: What is the proper size of return for a 3 ton 16 seer unit. Is having 2 return with 16x25 (16”) and 12x12 (9”) advisable? Also, we have 12 different size of vents in the house (3 rooms – master (2 vent), other room (1 vent each) , what should be the right size of duct supplies per each. I would appreciate if you could enlighten me. Thank you very much.   



One 16 x 25 return opening is good for approximately 2.5 tons. So, if you have the two 16 x 25 return grills, each on individual 16-inch flex ducts this alone is sufficient return air. The 12 x 12 helps. If the two 16 x 25 are twinned with only one 16 –inch flex duct, we recommend increasing  the 9-inch duct on the 12 x 12 to 12-inch to maximize total return air draw as it will only aid in circulation. Additional return air is not detrimental to the cooling system.


As far as the supply air registers:  The size and style of register depends on the size of the room, ceiling height, amount and type of glass and sun exposure to the outside wall. The key component is to have a grill that properly throws the air into a given room and to have a register that is not restrictive on the air delivery.   Depending on ceiling height ( 8-10 ceilings ) if the grill is located from the center of the room, we prefer a 3- directional grill. If the grill is located back further towards the inside wall we prefer a one way grill. This is designed to get as much coverage to the outside wall as possible.

Return Grille Sizing

Posted on 06.10.2014

Question:  How large does a return air grill need to be?  I have 1 right under my unit that is 7" x 32".  Is that enough?


Answer: The return size depends on the capacity of the cooling system, length of return run and size of the return chase. As a basic rule of thumb you can multiply the width by the height of the return grill and then divide by 144 to determine if your return GRILL opening is within range of the total system tonnage.   

Example: 12 x 24 return grill equals 288 square inches, divided by 144 equals 2 which represents about 2 tons.

Example: If you have a return chase or return duct over 12 feet long, then divide by 150 instead of 144. 7 x 32= 224 divided by 144 is approximately 1.5 tons cooling.

Return Sizing with Filtration

Posted on 05.08.2014

Q: I am installing a new unit and AC air return. What is the correct size of the return for a 4ton ac using a Dust Fighter™ 95. My chase to the attic coil is 24 x24 and 13’ long.(9’ vertical and  4’ horizontal to the coil in the attic)..........the return air is 24 x 30 and I want to use a  Dust Fighter™ 95 filter MERV 8 should I make the return air larger.  I cannot change the size of the chase thanks in advance for the help


A: It is our opinion that this a very restrictive filter to put in the wall that far away from the blower. The further away the filter is from the blower and the denser it is, the more it can affect the static pressure on the system. You also need to make sure that furnace can provide enough airflow to compensate for the filter restriction.  With this type of filter, you may need to double the return size and grill to compensate.


If possible, the best filtration application is one that is installed as close to the furnace return as possible.

Excessive Dust in Home

Posted on 10.15.2013

I have a problem with excessive dust use good filters replace regularly blower clean evap clean where is the dust coming from.


Infiltration is a source of dust. Also, the filter system is designed to reduce re-circulated material through the cooling system and ductwork. A filter’s job is to keep the equipment and ductwork clean. A lot of indoor/outdoor activity can allow dust into the home. Other causes of infiltration are: doors not properly sealed, attic access not properly sealed and canned lighting. If the material is fibrous and light in color it is most likely coming from carpets or cloth flooring (rugs). Also, the dryer being inside the house, linens and dry cleaning can also contribute. Ductwork infiltration is grainy and dark, unless you have white blown in insulation. Material coming from inside the house will be more fibrous and lighter in color. Sealing face plates and wall plugs can also help reduce infiltration.


Posted on 10.04.2013

What is going on with Complete Care?


To our customers who have recently received a letter from Complete Care (IAG), we would like you to know that we are (as always) committed to putting our customers first.

For more information on your warranty with Central City Air, please click here to download a letter from our President.

If you have any questions or comments, please e-mail us at: sdcp@centralcityair.com

Supply Shortage

Posted on 06.26.2013

What is the status on repair parts?


We have been experiencing a shortage on repair parts and supplies across all vendors. We have been doing everything possible to get our customers the parts they need (including running our President and Vice President all over town). Because of this shortage we may experience longer wait times as many parts have to be shipped in from out of town. We apologize for the inconvenience.

Extreme Summer Heat

Posted on 06.18.2013

What is your scheduling looking like in this extreme heat?


Due to the extreme heat and high humidity (with temperatures that feel like a heavy and humid 104 degrees most of the time day and night), we have been responding to our customers who desperately would like to be cool again. As a result we will resume doing maintenance check-ups in July. Should your A/C stop cooling please call we will get you cool again.

Two Stage Coil?

Posted on 08.30.2011

Dear Sir,

I found your address on the internet from a radio broadcast in Dallas, Texas. The reason I am writing is I am curious about the two-stage coil. I have two Goodman units that were installed in 1994. I know my coils have never been cleaned and the HVAC has never been sealed. The units still work albeit less efficient. What do your two stage coils cost? I know you are in Houston and I am in the DFW area, but I am considering either upgrading some components or doing a complete refit. I have a single story home with approximately 3000sq. feet. I think it is 2950sq. feet to be exact. House faces North and gets plenty of West sun. I like your web site as it is one of the more informative out there.

Just curious. What would a bid for say two units Lennox that are 16 SEER and have a 13 EER to qualify for the Tax Rebate run? New Pads outside. New whips and electrical connections. 80-85% AFUE . Media filter (Honeywell so I can get replacement filters at Home Depot). Seal the system completely. Add some return air to match the units requirement. I was told I was short on return air.


The existing 1994 Goodman equipment and systems are at the end of designed life. Now is a good time to have a reliable air conditioning contractor look at your whole house and design systems to meet your needs within the home envelope. The quality of the installation is critical to obtaining maximum performance from any system. When you start the process it is a good idea to make your goal a top quality install job, with a smart designed system that uses well engineered equipment.

If your goal is to get the tax credit that is simple and very easy to obtain from anybody regardless of the integrity of the contractor. Think about the SEER shell game our Federal government is inviting you to play before you participate. Our founder David Debien always used to say do not design for SEER design for performance. Central City Air will not use any of the AHRI approved evaporator coil match ups except on the 1Q 23 Maytag equipment. We focus on humidity removal in Houston, Texas. Energy rated equipment match ups may not meet the humidity removal requirements we need. So be sure to do your due diligence.

The split coil you asked about is a Central City Air propriety coil, designed by our Founder David Debien. They were designed specifically to work with the 2 stage condensers for maximum humidity removal. We only sell them to our customers in Houston.

Regarding your request for pricing on Lennox 16 SEER that is matched to meet the AHRI 13 EER for the Federal tax credit: We are Lennox dealers, let me encourage you to get your pricing from a Lennox Premier Dealer in Dallas. You can go to the Lennox web site to look for Premier Lennox Dealers in your area. Lennox has a 17 SEER single stage and a 21 SEER 2 stage unit you may want to consider. Let me also encourage you to think about your goal.

TX Valve size

Posted on 06.23.2011

If we were to install a 3 ton condenser and a smaller 2.5 ton coil, what size should the TX valve be? 2.5 or 3 ton?


Central City Air uses adjustable expansion valves properly sized and installed correctly this allows us to fine tune the regulation of refrigerant flow so that the right amount of refrigerant goes to the coil. This occurs under all conditions and keeps the coil as cold as possible, resulting in maximum humidity removal and maximum cooling performance. We do not use fixed expansion valves that cannot be adjusted. The Valve type you would need would be a "B" valve.

Vacation A/C Settings

Posted on 06.11.2011

I'll be on vacation for a month in July. i live in Houston. what would be a safe setting for my ac unit. i'd like it as high as possible to save electricity, but don't want it too hot so i don't hurt my electronics or have mold problems.


If you are out of town for a while we recommend between 81-83 depending in the summer. This will still allow the system to run and pull some humidity out of the air.

Rusting Plenum

Posted on 12.03.2010

Hey Dave, I am fixing to buy a house that is 5 years old and while inspecting it I noticed on the AC unit for the upstairs that the top of the plenum had large spots were it was almost rusted thru. The owners realtor is having a AC company come out tomorrow. What suggestions do you have that might be causing this? This system also has some sort of fresh air ventilation system on it( any comments about this). This house is built by Ashton Woods. By the way I am one of your students from awhile back. Thanks Pete


The rust spot is most likely caused by a torn or missing spot of insulation inside the plenum. We suggest having this looked at to make sure that there is no moisture build up.

How to Eliminate Dust?

Posted on 12.02.2010



If you do not already have a Fresh Air Intake installed on your system, you should look into getting one. If you have one already or are looking to install a new one, you should make sure that you have one that has a damper that is timed with the system. Some Fresh Air Intakes are installed on their own timer, which will randomly open and close. You need one that is tied into the system so it opens and closes when the system turns on and off.

How hard is it?

Posted on 08.12.2010

I've got a two story house and only one unit, The downstairs and upstairs are always quite a bit difference in temperatures, what is the best solution to this problem? How hard is it to retro fit the house with two units?


Over the past 15 years, we have solved this issue with 1 system in a 2 story home. Currently, all of your ductwork may be on one supply plenum. Air (like water) flows down the path of least resistance. Heat also rises, which allows the upstairs to get warmer.

Our solution is to install two plenums. The first is for all of the downstairs ducts and the second is for all the upstairs ducts with a section of round duct pipe in between on the end cap. The air will flow through the main plenum into the second plenum for the upstairs ductwork, allowing additional cooling to the second floor. This will make the air as cold or colder than the first floor when pressurized assuming the duct design is correct.

For heating, the section of pipe between the two plenums has a motorized damper, which in the heating mode, closes a percentage. This prevents over heating of the 2nd floor and better heating to the first floor.

Air Filter

Posted on 08.12.2010

What is the best type of air filter to use in the return air ? I've used the Filtrete 1000 (red) filter but it seems like it gets dirty fast, which I'm assuming makes the a/c work harder. I change them once a month, but they look pretty dirty after two or three weeks.


When space permits, we recommend an inline 5" pleated media filtration system within 1 foot of the furnace in the attic for greater filtration. If a filter gets dirty quickly, we recommend looking at sources of infiltration, such as leaking light fixtures, doors and windows. Also, carpeting and indoor clothes driers compound the issue.

Uncontrolled fresh air enters your house through cracks and crevices in your home, through the air conditioning system, and through leaks in the duct system. Uncontrolled fresh air can be very undesirable.

Also, the further the filter is away from the blower and the more dense the filter, the greater the restriction on system performance. The filter is picking up material like it should. Why is it getting so dirty in 3 weeks is the bigger question.

Higher humidity in house

Posted on 07.25.2010

House is two stories around 2400 sq feet with one Lennox 4 ton unit with a 5 ton ADP coil, two thermostats with zoned ducts. No issues cooling the house even on the hottest days.

The problems I am having are short run times and elevated humidty...around 56% on average.

I know that having one system with a two story house is not ideal and is the low cost option for most builders. Is there anything that can be done to lower the humidity


Humidity in the home, on average should be around 55% or lower. The 5-ton coil on a 4-ton condenser is too large. Humidity control is only a by-product of heat removal out of the air during the conditioning process. An oversized evaporator coil will not get cold enough to absorb moisture out of the air. The coil size determines the major balance between dry and wet heat removal. The coils remove dry heat (temperature) and the wet heat (humidity). The coil size determines this ratio. The larger the coil is size, the lower the humidity removal. In many cases, a smaller coil can increase the humidity removal by 30% to 40% resulting in greater dehumidification. After extensive research, we have found that having a matched or oversized evaporator coil will not control humidity enough. Rather it increases the humidity level in the home, especially at night. The reason is that the evaporator cannot get cold enough to properly dehumidify the air, causing your air to feel sticky and humid.

We recommend a 4-ton condenser with a 3-4 ton evaporator coil in the horizontal application. We also recommend an evaporator coil with an adjustable thermal expansion valve to help adjust refrigerant charge for maximum performance.

You also need to make sure that the home's envelope is correct. Make sure that the attic access, canned lighting , windows and doors are properly sealed and weather stripped. You may also need to get the home closer to neutral pressure to reduce moisture and dust infiltration, which can be achieved with a Fresh Air Intake

Blower Motor Runs Continuously

Posted on 05.26.2010

I have a York HVAC system, and the inside blower motor is running continously. In addition, yesterday, I noticed smarks coming from the capacitor outside of the blower housing. I turned the unit off, and there was also water dripping on the outside of the unit.

The HVAC unit runs fine today, but I didn't want to take my chances so I turned the unit off from the breaker box.


1. What is causing the water to be dripping down onto the blower housing?
2. What could cause the sparking (burned wires) on the capacitor?
3. What could be causing the blower motor to be continously running even when I turn the thermostat to "off"?


It sounds like the system has an iced up coil and the water is shorting out the blower capacitor. The blower relay may also be damaged due to the dripping water. You need to call in for service and check the filters as well as the refrigerant charge in the system. They also should check for a dirty coil and blower wheel.

A/C Condensing Coil Freezing Up

Posted on 05.08.2010

The problem we have is our a/c condensing coil freezes up, causing the house to not cool properly. It seems to be happen during the late afternoon/evening, when the temperatures get warmer and it gets more humid outside, which causes the system has to run more.

In March 2005 we had a new Trane a/c and heating system installed in our 2396 square ft. - two story home. We also had radiant barrier paint installed in the upper and lower attic's, and additional bat insulation installed in the attic floor. The house was a combination of brick and vinyl siding; however, during the summer of 2008 we had the vinyl removed and had hardi plank siding installed, along with new insultaion. We also had our standard windows removed and had new insulated windows installed. The a/c condensing coil has frozen up each summer since installation, and when this happens water drains out of the overflow line on the side of my house, but the company who installed the system was unable to determine the cause.

On May 6, at approximately 10:00 p.m., the temperature upstairs was 82 degrees, even though the thermostat was set for 72 degrees.

On May 7, I called the company that installed the system and they sent out a technician who discovered the condensing coil in the attic was leaking freon. The Tech then checked the freon at the outdoor unit and discovered that the freon was low by about 6 - 8 pounds. The Tech stated that this could be the cause the condensing coil to freez up, but last June the same condensing coil froze up and they checked the condensing coil and it was fine.

The Trane components are a 4-ton variable speed blower - two stage gas furnace w/ comfort R, a 4-ton XL16i - two stage condensing unit, a 4-ton TXH high efficiency coil, along with an Aprilaire electronic air cleaner, all were installed in March 2005.

Since the company has been unable to determine what is causing the a/c to freeze up, we are now wondering if the system that was installed is sufficient for the size of our home.

Your thoughts on our situation would be greatly appreciated. Thanks!


I do not believe capacity is the problem for the system freezing up. A freeze up is generally due to loss of refrigerant or lack of airflow. You may not have a leak in the coil, maybe a leak in the refrigerant lines in the wall. When the siding was replaced they may have kicked the copper. A good leak tester should be able to locate a refrigerant leak.

You may also have issues with the comfort and not having the airflow settings correct. Have the contractor leak test the system and Freon lines to check for any leaks. Also have them check his airflow settings.

Dirty sock syndrome

Posted on 12.22.2009

Do you have an update to this stinky issue. I seen this info on this link and was wondering if you had any updates to help with this.


There have not been any advancements in combating the “Dirty Sock Syndrome”. We continue to use the Bronz-Glow coating to great effect whenever we have a customer who has this issue. It is still the best thing out there.

Veritcal or Horizontal Unit

Posted on 12.11.2009

We are looking at doing a fairly large additiona to our small 1930's home and we are having a very hard time trying to figure out how to fit the a/c units and duct work in. we are thinking about maybe doing a verital unit? are vertial units better or worse than the horizontal units? do you have a preferance?


When space permits, the horizontal application is the best approach. A horizontal slab coil with an adjustable thermal expansion valve allows for a colder coil, which will dehumidify and cool the home much better. Also, the horizontal coil application will have an emergency pan directly under the coil to catch overflow. They can be cleaned and serviced much easier than upflow coils.

Upflow coils are very difficult to access for cleaning. The design does not allow for the aggressive cooling and humidity control required along the gulf coast. The basic design has the evaporator coil placed on top of the furnace, so any overflow falls down onto the furnace. However, a good upflow installation is better than a tight limited service application with horizontal equipment. Installation and quality work matter in performance!!