Steps to Inspecting an Air Conditioning System
A simplified way to inspect your air conditioning system without a home inspector’s tool kit.
This is actually called the HVAC (heating, ventilation, and air conditioning) system.With Houston’s climate dictating a heavy use for this equipment (Houston is one of the most air conditioned cities in the world), a big concern here is how long will a HVAC system last? My answer is a resounding who knows? All joking aside, this system is composed of several pieces of equipment, which could last a good twenty years if it is maintained well. By this point, the unit will not be as efficient as you would want it. An HVAC system needs special equipment to really examine it correctly, but I will give you a means of testing this for yourself.
Lets start with how an inspector examines a typical system. In Houston, I have never come across a swamp cooler. I think these are common in Arizona, and on my old Beetle. Mainly we have gas or electric powered units with a condenser (also called a compressor) units. Some homes use heat pumps. More experimental systems are not common here.
The components of a typical HVAC system include: furnace, condenser, plenums, ducts, fan, and evaporator coil.Following the air movement through the system, we first come to the return air duct. For best results a home should have a return air duct in every room, but generally you will find one return duct on each floor of the home. These ducts have a filter in them. For energy efficiency’s sake, you will want to change these filters out once a month. This is why I suggest the cleanable filters to clients. If the filter is dirty, the unit has to work harder to draw air through it. If there is no filter, all of that dust is going into your equipment ruining it. Moving along, the air is going through a duct to the return air plenum. In older homes, builders would place wiring and gas tubing through these ducts, since it was a convenient space. This habit is a great fire hazard, since a fire caused by the wiring or gas line would be fed by the air passing through this duct. This is a hard problem to fix in most cases. Two solutions could be: 1) placing sheetrock all the way up the duct to the return plenum, thus covering the wiring and tubing; and 2) running a large duct tube through this duct from opening to return plenum. The return plenum is just a box which accepts the return air ducts. It will be in the attic before the fan. This box should have no holes in it. You would be able to feel air being sucked into the box if it did have a perforation. The next part of the system is the fan. The fan is called a squirrel cage. It is round, and looks like a big hair dryer blower (sorry, but I am trying to come up with a description everyone could picture). The common issue will be the motor is not functioning, the bearing allowing the fan to turn freely is worn, or the fan is bent or damaged. You will be able to tell by the sound. Noisy and vibrating is not good. You should hear the smooth hum of an electric motor, and the spinning of the fan. The fan will have a removable panel on it, so you can look at it. Pliers would be able to remove the machine screws on the unit. (On some systems the fan can be the last item before the supply plenum; however, I generally see it first.)
Next we come to the furnace. The furnace should also have a removable panel. Half the units have a panel that will slide out, and the other units have a panel that has machine screws holding it in. Machine screws cannot be undone with a screwdriver. You either need a nut driver, or a pair of pliers. Wether gas or electric, there will be a tube coming into the unit. Where it enters, there should be a grommet (think gasket) preventing this tube from being damaged by the housing. For gas units, there should be a shut off valve nearby, and for electric units, there should be a switch (breaker or light switch) close. Check to see that the wiring looks to be in good condition. Here is the hard part, you will want to look at this compartment where the burner or electric coils are, but you will not always be able to. A complete inspection means pulling this equipment out, and a HVAC technician should be the only person to do this task. While the heater is running, look to see the flame or heated elements. The flame should be a nice blue flame. The burner compartment should be rust free. If you have the equipment, you could check the elements for an electric system to see if they have power.
Going forward, the air now passes through a transition plenum to the evaporator coils. This is the box with a pan under it. The pan is for the secondary drain line from water condensing on the coils. It should be clear of debris, and have no water in it. This is the cooling part of the system. The coils have a refrigerant in them, which cools the air down. This refrigerant is pumped to the outside condenser. A condenser and a compressor are the same thing. The outside unit has both pieces of equipment in them, so both terms are used. This unit is basically a big box with a motor, a fan, and tubes with fins running around it. The refrigerant exchanges heat with the air passing over the coils in the evaporator, and then passes that heat to the exterior. A heat pump is a device that can operate this system in two directions. Instead of a furnace, the pump takes heat from the outside air to the evaporator coils in winter, and then it reverses this process in summer. (There is always heat in the air; go back to your Middle School Science lessons). On the condenser listen for loud noises and vibrations. Look at the fins to see if they are damaged. Check to see that the wiring looks good, and that the refrigerant tube is covered with an insulator. The condenser should be three inches above ground level. The unit should have good clear space around it. If there are two condensers, they should be separated by eighteen inches. There should also be a way to turn off the power close to this unit. Either a dedicated switch in a box, or the service panel should be close by in sight.
Going back up to the coils in the attic, we will follow the air to its last stop before going to a room: the supply plenum. This is the box with multiple ducts coming out of it leading to the different rooms. If you are a lucky, there will be dampers to zone the air to the various rooms. The air is being pushed out at the same rate to all rooms, but rooms further away from this plenum will not receive the same air movement that air closer to the plenum gets. The way to check this without opening up this box is to feel how strongly the air is coming out of the return air vent (register) in all of the rooms of the house. In the attic, you have a problem when you feel cool air your plenum has a perforation. Air conditioning the attic is nice for those of us who have to be up there, but it will cost you in your utility bills. The air now goes through ducts to the individual rooms. The ducts should not be crimped (tight angles). They should also be supported from the rafters. The ducts will have insulation covering them, and joints will have a reflective tape (not duct tape). Check for leaks in the ducts by feeling for air.
Finally the air is in the room.If you have the tools, you will want to check the temperature differential. The temperature differential (delta T) is the temperature of the air into the system subtracted by the air out of the system. If you are measuring by the coils, the difference is acceptable when it is within 20F. If you are measuring at the supply register and the air return register, the difference is acceptable when within 10F. For the register method, you need the average of all return and supply registers. Over the coils will tell you if the coils are good, but from the registers tells you if the system is fine. Without temperature meters, I would not suggest trusting your sense of feel. We do not sense temperature as well as we sense comfort. You feel comfortable with air movement, which makes us feel cool, but does not tell us if the temperature is good. If these parts are maintained or repaired, a system could last quite a while.
Most systems are replaced by newer units for energy efficiency reasons.SEER is a rating system to determine how well the system operates. Currently units are trying to out do each other in this regard. A Seer above ten is good, but the standard is quickly moving up. Probably a better measurement for you to check if the unit is right for your house is the tonnage of a unit. The usual number is you need for every 500 square feet of your house you need one ton capacity. Take the square footage of your house and divide it by 500. Compare this number to the “tons” number on your condenser. Hopefully, your condenser will have the same number. For example, a 2000 square foot house will need 4 tons (2000/500=4). Actually, you will not want to oversize this unit (have a larger number), since this will prevent the unit from dehumidifying the air, so slightly undersizing the unit is better. Lastly, run the unit for fifteen minutes before you start to check the HVAC system. You will not want to run the air conditioner when the temperature is 60F, since this can damage the evaporator coils.
One more thing to check is the circuit breaker for the unit. The condenser has a maximum amperage on it tag. This should be the number (size) on the circuit breaker. It is the amount needed for when the unit starts. When you start seeing problems with any part of this system, you should check to see if a repair is possible or if a new unit is needed. If the furnace or the evaporator coil needs to be replaced, the other part will have to be replaced, since the components are matched to work together. So how long will an HVAC system last? OK, hate me, it depends.
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