What are your symptoms?
This is most likely a bad blower motor or a bent or damaged wheel.
Ok the first thing you need to do is securely, set up a ladder to the roof. Now make sure the thermostat is turned to cool, auto and at and least 10 degrees colder that the temperature in the home so the unit will be trying to run. Now make go to the unit and remove the panel that has the blower motor inside. Once the other parts in the air conditioner turn on, wait 5 minutes and touch the motor with your hand. If it is hot it needs replaced. If not then try spinning the wheel. If it does not spin at all or has trouble spinning then you might need a new wheel and motor. Never just, change a motor as when wheels go out motors take damage. Even if the motor starts working again, it will stop again very soon. If wheel does spin smoothly, you are going to need a voltmeter.
Find out where the white ( sometimes there is no white it’s yellow instead) and black blower motors wires connect to and check for 240 V if you have power then you need a new blower. If you do not then you need to make sure there is 24 volts coming up from the thermostat wires. Check the blue (common) wire and the green wire (sometimes green is brown) for 24 V. If you have 24 volts and do not have 240V where the blower motor plugs into then the part the motor is plugged into (circuit board or the contactor is bad).
Ok, if nothing is happens the first thing you need to do is replace the batteries in your thermostat. If that does not solve the problem, check the circuit breaker. Open the panel and look to see if any breakers are tripped. If you do not see a breaker that is not fully on then try resetting the one to the air conditioner, it should be a double throw breaker usually a 40-60 amp. If this does not solve your issue, go up to the roof and check the disconnect, if that is tripped reset it. If not you will need to open the electrical panel on the ac system. Once open look for blinking lights. If there is a blinking light, count the flashes and reference the schematic, to see what the error code is. No lights at all, check power coming into the contactor. If you have power, then check power coming into the circuit board if the board has 240 V in and no lights flash, you need a new circuit board.
Most people do not know it but your thermostat usually takes batteries. All you have to do is remove the cover, sometimes you have to pull hard or use a screwdriver to get it off. Replace the batteries, and you should be ok. If you still have nothing, replace the thermostat.
There are three things, which can cause an air conditioner to ice up.
Now the first is the easiest to check and to repair. Simply visually inspect all four items. The air filter we all know where that is. The coil and blower motor, those are inside one of the panels of you air conditioning system. If the coil is dirty, turn power to the air conditioner off and clean coil with a brush and spray with a garden hose. Alternatively, call a professional air conditioning repair company (the Air Doctor), and we can come clean it with acid. The return air is simple also, it is in the attic, if it is crushed, it needs replaced.
This is an easy one 98% chance you have a bent blower wheel. The blower motor in the air conditioner spins at 1175 rotations per minute, if a wheel is bent even by a millimeter, it will vibrate like crazy.
Here is another easy diagnosis, 95% chance you have a refrigerant leak. Look around in the unit all around the copper lines. What you are looking for is oil, refrigerant is oil based. Wherever the leak is will usually have wet oil on it. As far as the repair for this, I would not advise attempting something like this on your own. To properly repair this, you will need many pieces of equipment and will need to evacuate/recover unit, braze leak, purge unit with nitrogen, vacuum unit, then charge system to the proper superheat and sub cooling. This will require an extensive knowledge of air conditioning dynamics and ac 101 theories. Call the Air Doctor to get a professional to help you.
This is usually a sign of a bad condenser motor. Try turning the power off and touching the motor, if it is hot to the touch it has to go. The only other things this could be are burnt wires going to the motor (visually inspect) or, a bad capacitor - remove all wires from capacitor and check across both terminals with a voltmeter on microfarads. Reading should be within 5% of the rating labeled in side of cap.
Oh, no that is usually about as bad as it gets. 98% of the time, that is a sign of a grounded compressor. The breaker keeps tripping because inside the compressor, there are wires that have corroded to the point of having no more insulation left on them, and they touched the side of compressor metal and arced to them permanently. The wires, welded themselves to the metal inside the compressor. This can be checked by removing the cover of the compressor. Remove the wires; get your voltmeter set to continuity. Now place one lead end directly to a piece of copper (scratch it into the copper to expose fresh clean copper, now touch the other end to all 3 places you pulled the wires from. If any of them beep, the compressor is toast. Call a professional AC repair technician. The Air Doctor can come do this for you, at a lower rate than most air conditioning companies do. (702) 243-4000