Converting a marginal system makes an even more marginal system. The tuning (repairing) of a marginal system is anything but cookbook diagnostics.
The proper working of heater water valves, recirculate doors and other air distributors are a must before approaching the thermodynamics of the refrigeration process.
There is no "repair in a bottle" for these problems that I know of.
[This message has been edited by stevebfl (edited 06-25-2000).]