Ok, Your AC is broken and a repair service needs to help …...
First, a few things about repairing AC units. New units can be trouble free for a long time, but when problems start to occur, they may start to become a regular thing. As units get older, they lose capacity and efficiency, so sometimes it is better to replace an older system than start dumping repair money into it. Often the energy savings of the upgraded system will pay for itself within 5 years or so. All said, maybe you just need it repaired this time, or the equipment really isn’t that old. Sometimes they can just break down.
The serviceman often works for a company on a flat rate basis, or gets bonuses for up sells. That is, sometimes the service guy is also a commission salesman. This in itself is OK, but you need to watch not to be hustled. This page should educate you enough to be a wary customer. Also, unskilled technicians can misdiagnose the problem, and you may be replacing parts until it works.
As with the rest of businesses, the cost of labor has gone up quicker than product, and service time is expensive. Remember, you are hiring a skilled tradesman. He will be refrigerant technician, electrician, plumber and controls expert all in one. On top of this, he has to work in hot attics, and in freezing cold, so a typical service technician is well paid. On the other hand, a fair and honest diagnosis is worth the cost. All said, here are some symptoms, and what they may mean. You know it’s not working, and you checked the items as a homeowner on the previous page. Now lets look at some possibilities.
OUTSIDE AND INSIDE UNIT RUNS, BUT NOT COOLING: Air is blowing through the ducts, but its not cool, and the outside fan is running. Air temperature from the outside fan is same as outside temperature.
Probable: Compressor is not running, or is so low on refrigerant that is will run for a while, overheat and shut off for a while. Could be bad start and/or run capacitors for compressor, burnt terminals, bad contactor (compressor relay), or bad compressor. If compressor itself is extremely hot, it may be off on thermal overload. The compressor depends on refrigerant gas to cool itself as well, so being low on charge will overheat the compressor. If the air from the top of the unit is very hot, the problem is probably an outdoor coil blocked with grass, leaves, or mud, and it is overheating as well. The all may be well, but the system is a little low on refrigerant charge, and just can’t keep up. Dirty coils can be the problem too. (see COILS below for more info. Normal conditions would be: air from top of unit warm (20 degrees warmer than outside temp), and large copper line cold to the touch. The small line should be slightly warm, or moderately warm.
OUTSIDE UNIT NOT RUNNING, INSIDE UNIT RUNS: If we already verified power is good to the unit, then we can look at a few things. Probable: The fan motor may be bad, or have a bad capacitor, so it is not running. But what about the compressor? Well, it would run for a while, but shut off on its high temperature switch, or overload. When it cools, it will run for a little again. Or, you may have a bad contactor, (compressor relay) that turns on power to both fan and compressor. Or maybe a defective thermostat, not sending a signal to the unit, or simply a broken thermostat wire (gardener with weed eater). The thermostat wires are the two small wires that usually run taped to the copper lines.
OUTSIDE UNIT RUNNING AND INDOOR UNIT RUNS, ICE ON COPPER LINE: We discussed this on a previous page. Probable: No air flow over indoor coil, (bad indoor fan motor, relay, or capacitor), blocked filter, low refrigerant charge.
NOTHING RUNS, INSIDE OR OUT: It is just stopped . Probable: Again, after power is verified, a problem in the control system. Bad transformer (to make 24 volt for thermostat), blown mini-fuse, bad thermostat, bad control board, or maybe, just a float switch doing it’s job. The float switch is a protection device that shuts the system down if the secondary, or emergency drain pan fills with water. These are optional, and are not always installed, but they are a nice thing to have to save your ceiling.
OUTSIDE UNIT RUNS, INSIDE IS OFF: Usually will be iced up as well. Probable: Stuck contactor on outdoor unit, bad blower motor, capacitor, or relay inside.
REFRIGERATION PROBLEMS: This would be a diagnosis for a skilled technician, but generally refrigeration problems are based on restricted lines. The system is closed and should stay clean, but a failing compressor can start to clog the refrigerant filter, and give odd results. The actual refrigerant control device, or TXV can fail, open, closed, or erratic, and create problems. The indoor and outdoor coils have to be kept clean in order to transfer the heat required, and clogged coils (often not visible) will throw things off. Luckily, refrigeration failures are not as common as other repairs.
REFRIGERANT LOSS: I often have customers ask me how much “Freon” they should expect to add every year, and the answer is none. The refrigerant system is sealed and closed, and if any needs to be added, it has leaked out. Most common is minor leakage at the connection fittings for technicians hoses, but these fitting should be snug and capped not to leak. Although a loss of a pound a year is not really troublesome, it does cost money to top off, and means your system is not at peak efficiency. Tracing leaks can be quick or slow. Some leaks may be underground, or in walls, and very difficult to locate. We cannot give a fair quote to locate a leak, We can only search until it is found. Most technicians use electronic “sniffers” that can detect minute leaks, but they take some skill to interpret correctly. A technician can make a detector squeal like a leak without actually finding one. They also use good old soap and bubbles, or sometimes inject a fluorescent dye into the system, and return later to search for the leaky spot with a black light. Different methods work better on different leaks. Leak detection takes time and patience, and time is expensive. Here are common leak areas: Hose connections, threaded fittings, corroded evaporator coils, corroded liquid filters and sight glasses. Correctly welded copper lines should just not leak, although I have rarely seen 10 or 15 year old joints start to leak.
COMMON SERVICE TRIP “UPGRADES”: Here are some common service call up sells that you may be presented with to consider.
1) Coil cleaning; Tech offers to chemical clean indoor and/or outdoor coils. True, coils need to be clean, but a true chemical cleaning is not a routine maintenance item. The outdoor coil can usually be cleaned out with a garden hose, and the indoor coil should not need serious cleaning more than every 5-8 years. And then, a good cleaning is not just a spray, soak, rinse process. If you pay good money for a cleaning, make sure it needs it, and gets done right.
2) Float Switches: As we spoke about earlier, can be added to your secondary drain pan to shut unit down if it fills with water. Not a bad investment.
3) Programmable Thermostats: Theory is that you can program your thermostat to “backset” during hours you are not home to save energy costs. Long story short, the savings you realize may be about 6% on hot/cold months, and you can do the same manually if you remember, like turning out the lights. Some people find the programming confusing (like setting a digital watch!) and don’t bother. On the other hand, if you follow the instructions, they are useful and do work.
4) Duct sealing: If your ducts are leaking air into the attic or elsewhere, you are losing money. Most duct sealing, however, should take an hour or so, unless you have major duct issues. Just verify the problems before you get sold on a $400 duct seal job.
5) Service Contracts: If you like the company, these are generally a good deal. Expect them to come out twice a year, make minor repairs and service the units all inclusive. Most companies will also put you on a “priority” list for emergency service, and offer discounted charges to regular customers.
6) Adding “Freon”: A tech can also hook up to a system and squeeze in a little refrigerant gas. He may tell you 4 lbs. The jug should be scaled before and after usage to verify. Again, adding gas should not an annual event!
MORE ABOUT CHEMICAL COIL CLEANING:
You have two coils involved in your conventional AC system, and both need to be clean to keep efficiency up, in in extreme cases, dirty coils may make your system just not cool well at all. First a warning. “ Coil Cleaning” is a common service call “up-sell” and unfortunately many coil cleanings are unnecessary, or even damaging. Chemicals can be harsh, and if left on improperly rinsed, or used too often, can lead to pre-mature coil failure. Most coils can be cleaned with water spray and soap solution unless there is heavy grease buildup, or outdoor corrosion. Generally cleaners are one of three types, ACIDS, ALKALINES (opposite of acid, and also corrosive) and DETERGENT. In general ACIDS are used for corrosion buildup, or mineral deposits. ALKALINES are superior at cutting hair, tars and grease from coils, and DETERGENTS are an all purpose cleaner for most applications. The acids and alkalines are hazardous, and for use by professionals only.
EVAPORATOR COIL is your indoor coil, or cooling coil. It’s job is to transfer heat from your indoor air to the refrigerant gas to be expelled outdoors. If this coil gets dirty, you lose efficiency of transfer, and your air blowing out of vents will not be as cold as it should, and the system Superheat will be low, that is, the outside line will be ice cold to the unit. This needs to be diagnosed with technical tools, but generally, if your outside line to the unit is very cold, and the air blowing out of the vents is not very cool, a dirty evaporator coil is a likely culprit.
Cleaning this coil is not very easy. It will always mean entering the duct system, and depending on your system may be accessible through the air handler, or through duct access hole cut into the duct. If dirt build up is heavy, this can be a tedious job, best left to a pro.
CONDENSER COIL has the job of extracting heat from the compressed refrigerant just enough to “condense” it, and this heat is then blown into the air outside your house. This heat represents the heat extracted from your home, along with waste heat from the compressor. If this coil gets dirty, the unit will not properly condense the refrigerant, and you start to lose cooling efficiency quickly. You will also lose capacity, and in extreme cases, the system will not seem to cool at all. High pressure will increase, and system overall performance will be poor. Luckily, these coils are easy to access, and usually need no more than a good hosing twice a year. They get cluttered with leaves, grass cuttings, or in dusty locations can load down with dust quickly. In corrosive areas, such as seacoasts, and industrial situations, they can corrode quickly, and be ruined within a few years. All aluminum (Trane) coils are more effective in these areas. If years have built up mineral deposits on these coils, sometime acid cleaning will work, but much of the damage is done. Sadly, outdoor coils slowly lose their capacity from the day they start running. This is one of the reasons we often to recommend to replace a 10 year old system that still runs OK. You may find that the energy savings alone will pay the difference back over 5-6 years.
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