There are several types of ‘acoustic’ guitars; Steel strung (the most common type), Classical (with nylon strings), Electro-acoustic (any acoustic guitar fitted with a pickup) and Semi-acoustic (really an electric guitar with some parts of the body made hollow, also known as semi-solid).
Each of these types has a great deal in common with electric solid guitars. Work on the nut, frets and tuners, is more or less the same as on a solid guitar. However, each type of acoustic can have its own particular problems.
Steel Strung Acoustics
All (well nearly all) acoustic steel strung and classical nylon strung guitars have a non-adjustable wooden bridge, with a plastic or bone saddle. (If the saddle is plastic, then replacement with bone will always improve the tone.)
Setting the height of the saddle is an essential part of the set up process. On an acoustic guitar this involves either lowering the existing saddle, or replacing it with a taller one if the action needs to be raised.
The intonation is set by shaping the top of the saddle (seen most commonly on cheap moulded plastic saddles). Many top quality acoustics (Martin, Santa Cruz, Collings, Gibson) have good quality bone saddles, but no intonation compensation. This saves time in the manufacturing process, at the expense of tuning accuracy.
In addition to the saddle height and intonation aspects covered in the above section, most classical guitars have no means of adjusting the neck. (Almost all steel strung acoustics are fitted with a truss rod to adjust the neck relief.) If your classical guitar has too much neck relief, then the best way to straighten it is to use a special ‘compression’ re-fret technique, which uses frets with wider tangs (the part that fits into the slots on the fretboard), to wedge open each slot slightly. I have had great success with this difficult and time consuming technique. (My own 1979 Petersen classical was suffering in this way when I bought it… not any more!).
These can be either steel strung or (less commonly) classical, nylon strung guitars. Uneven string volume (through the amp) is most often due to an incorrectly shaped saddle (a set up will cure this). Otherwise, work on this type of guitar involves repairing / replacing electrical parts, such as wiring, preamps, sockets and pots.
Since these are really electric guitars with hollow or semi-hollow bodies, problems specific to this type of guitar usually involve work on the electrics.
The difficulty here is one of access to the wiring and pots, socket etc. Since there usually isn’t any kind of back plate to get at the wiring, the whole lot has to be pulled out through the pickup holes (if possible) or through one of the ‘f-holes’. After the faulty parts(s) are fixed / replaced, the entire wiring must then be reinstalled through the (very small!) hole from where it came. This resembles key-hole surgery and is the main reason why many guitar repairers refuse to take on this type of work.
Please be aware that electrical repairs on this type of guitar are always more expensive than on solid body instruments.