Here is a list of mechanical equipment manufacturers. Not all are listed by any means, only the most common. It is most useful when tracking these parts to have both the model number and serial number of the equipment you have. Furnace and air conditioner problems can not be thoroughly diagnosed over the phone. Even common symptoms usually need a tech with test equipment to verify a problem. Equipment is complicated enough that different parts may result in the same problem (i.e.; furnace won't start).
Furnaces / Air Conditioners: