[LazyPup]

Before you call someone there are a few things you can check on your own..

1. The leading cause of reduced air flow or complete system failure is a dirty air filter. While discussing air filters there is another point I would like to strongly emphasize. Far too often the homeowner opts for the high Merv rating filters as opposed to the conventional fiberglass mesh type. That in itself is great because the higher the MERV rating the finer the filter medium material and consequently the more dirt and debris it will trap, but High Merv filters cost two or three times the price of the conventional filters and people are then lulled into the false economy of expecting it to last much longer. Such is not the case. The actual amount of air that can pass through a square inch of high filtration medium is much less. To compensate for the reduction in air flow through the medium high filtration filters are made in a pleated form that greatly increases the actual amount of surface area. While the filter has a much greater surface area it is also trapping much smaller particulates, therefore the air flowing through the filter will obviously be cleaner but then end effect on the filter medium is that due to the increased amount of dirt trapped by the filter the filter will actually clog faster.

For peak efficiency, especially in a hot and dusty enviroment like Texas I would suggest you get in the habit of changing the filters monthly. This may seem a like overkill but consider the actual cost involved. Typically you can buy a case of 12 filters for about $12 to $24 at any HVAC supply house and in most Home Supply Centers. Changing the filter monthly will then cost you an average of $1 to $2 a month. Operating a system with a dirty filter can nearly double your run time and consequently double the cost of the electrical energy to operate it. In addition, if a system is operated for an extended time with a dirty filter you run a serious risk of the coils icing up and potentially icing all the way back to the compressor, which is one of the leading causes of compressor failure. With all things considered, even changing a $5 high merv filter monthly seems like a bargain to me.

2. Check all return air vents to make sure they are not obstructed by furishings or personal belongings. Even a partial obstruction on a return air vent can have a dramatic effect on overall air flow. My rule of thumb is there should be no furnishing or personal possessions within a space eqaul to the diagonal measurement of the grille.

3. Do not run ceiling fans when the AC is on. Ceiling fans create very strong air currents that often interfere with the designed air flow of the AC system. I once worked on an AC in a large one story on slab house in Florida that had three bedrooms on one end of the house, a very large living room in the center and the AC evaporator in a utility closet on the opposite end of the living room. The house was very well insulated new construction and the system had been engineered specifically to the heat load needs of the structure yet the living room, family room and kitchen were quite comfortable while the bedrooms remained an untollerable 90degF. For four consequetive days we checked the condening unit, evaporator unit, all fans and refrigerant pressure and all was perfect, but the bedrooms remained 90degF. There we were, three service techs, the Rheem Field rep and our company president all standing outside by the pickup discussing the problem when the lady of the house came out an announced, "Whatever you did, its working great now, the bedroom is 72degF. We all stood there dumbfounded, what had we done? We went back inside to see what had changed and as we entered the living room it was darker than usual. Someone snapped the overhead light on while we were looking in the utility closet. A few minutes passed and the lady came out of the bedroom area to announce it was getting hot in there again. We all agreed that the only change was turning the light on and surely a light could not effect the AC but when we looked up at the vaulted ceiling there was the answer. The ceiling light was a fan/light. A follow up smoke test revealed that when the ceiling fan was running it caused a down draft to the center of the room, which then spread across the floor and caused a backdraft pressure in the hallway preventing the return air from coming through the hall, across the living room and back to the unit. We were then confronted with two options. !. We could have installed a dedicated return air duct at a considerable cost or 2. Instruct the homeowner not to run the ceiling fan when the AC was on. (Can you guess which solution the homeowner opted for?). Having learned a valuable lesson there, I now make it a practice to check for ceiling fans any time there are erratic temperature variations and far too often that proves to be the problem.

There is a very simple diagnostic test that you can perform to get a fairly accurate indiction of how well your system is performing. Using a pocket probe type thermometer measure the temperature of the air entering the return air duct closest to the unit, then measure the temperature of the air discharging out of a supply grille closest to the unit. The air coming out of the supply grille should be approximately 12 to 15degF cooler than the return air entering the unit. If it is less than 10degF or greater than 20degF you should first change the filter and repeat the test. Repeat the test again in 20 or 30 minutes. If the temperature differential remains less than 10degF or greater than 20degF you should have the unit checked by an HVAC technician.