In my estimation a technician not only needs to understand how the various components work together but he also needs to understand that commercially available components seldom will exactly match the design requirements of a given system, and since system design is normally based on estimated peak loads, the system may often have to operate at conditions other than design conditions. More than one combination of components may meet the performance requirements, the efficiency of the system normally being dependent on the point at which the system reaches stabilized conditions or balances under operating conditions. We know that the capacities of each of the three major system components, the compressor, the condenser, and the evaporator, are each variable but interrelated.
The compressor capacity varies with the evaporating and condensing temperatures and the factors involved in the variation in evaporator capacity are quite complex when both sensible heat transfer and condensation are involved. For component balancing purposes, the capacity of an evaporator where both latent and sensible heat transfer are involved (a wet coil) may be calculated as being proportional to the total heat content of the entering air, and this in turn is proportional to the wet bulb temperature. So because of the many variables involved, the calculation of system balance points is extremely complicated