I get a lot of questions about running an air conditioner on a power inverter. The air conditioner is one of the hardest household appliances to run off of an inverter. The first thing to do when getting ready to run an air conditioner on an inverter is to get all of the specifications for the AC unit. The most important spec that you will need is the LRA rating. What this stands for is locked rotor amps. The LRA rating is what the AC unit will draw from the inverter while the compressor starts up. This is a very important spec when sizing an inverter for use with an AC unit. After you get this spec you will multiply it by the voltage and this will be the startup wattage needed by the inverter.
For example if your LRA is 60.6 amps if you multiply this by 115 you will get roughly 7000 watts at start-up.
The next thing to take into consideration for a AC unit is battery bank size. The best batteries that we have found that work well with inverters are the 6 volt golf cart or solar batteries. These are more cost effective and on average have higher amp hour ratings then the traditional group 27 12 volt deep cycle batteries. The 6 volt batteries will be connected in series. This will double the voltage to 12 and keep the amp hour rating the same. The inverter will see this as one big 12 volt battery. Your average 6 volt battery is 220 amp hour and sells for approx. 65.00. and your average deep cycle 12 volt battery group 27 is 115 amp hour and sells for 130.00. So if you get two of the 6 volt batteries it is twice the size at 12 volt s and you pay just about the same amount . If you want any kind of run time with a air conditioner it will require a large battery bank. I would have to say a minimum of 4 6 volt batteries wired in series to get longer then an hour. One of your best sources for the 6 volt batteries is a golf course. Reason for this is because the golf courses will really only use the battery for 6-9 months before getting rid of them.
Your next step in setting up a system for use with an AC unit is finding a sufficient recharge source for the batteries. You will want to have a minimum of a 150 amp alternator to recharge a system with a small AC. There are also many other options avaiable such as solar, wind or hydro.
This will get you started. I will post more about air conditioners and inverters as the questions come in.