A condensing unit specification is an official document that describes the complete list of components included in a standard thermostat. The current thermostat that you have installed is a two or three digit number; there is no formal requirement for it to be an exact one hundred and seventy-three for any given year. An alternative to keeping a regular listing of this information is to use a manual based system where it is possible to specify which part of the list is needed. This will mean that if you choose to do this you should do so as close to the actual manufacturer specifications as possible.
Parts of a system are different from devices in that they must have both a motor and a cooling or heating element in order to function. A typical option to be considered would be the original thermostat that comes with the system. It has a motor and heat radiator but not necessarily both of these elements. The motor can have a blower, which could offer significant savings on heating costs but also a chance for errors with the way it functions. This is especially the case when the blower may not always be going properly and may cause problems down the line.
One thing to remember is that even though a condensing unit specification may cover all elements of the unit, the actual part that operates the thermostat is the part that you will have to consider personally. If you are installing it yourself then you will want to ensure that the electrical component is secure and if you have any concerns for safety then you will need to call the manufacturer. It is generally safe to assume that if you have a working knowledge of electrical wiring you will be fine however there are no guarantees and you do need to be careful about what you place on your home.