The other day it started smelling hot inside the air handler cabinet. Upon examination I found what appeared to be one of the black power wires lying on cabinet floor with insulation melting and fan motor had stopped. I called a tech who plugged wire back in to terminal on top of one of the breakers which only made fan run on slow peed' his prognosis was that ineeded a new 500.00 motor. After he left I switched the black wire to the other breaker and got it to run on fast speed, but my problem is that the fan is not kicking off at all now.

By doing that you obviously bypassed the relay switch controlling the thermostat that's why it won't come off and on any longer. Call out someone else to look at this before you end up doing more damage to your unit by having it essentially hard wired into the motor. The black wire needs properly replaced if it started to smell and the insulation melting. Does not sound lieka good situation to let continue.