AC compressor fan comes on for a couple seconds then shuts down.
 

Looking for insight please to a possible cause of this problem.

When the contactor engages the compressor fan comes on for 1, maybe 2 seconds and then the contactor disengages, turning off the fan. The fan isn't on long enought to get up to speed. Press on the contactor (with an insullated screwdriver) and the fan will come up to speed. Remove the screwdriver and the contactor disengages.

Thanks! :)

check for constant 24VAC to the coil on the contactor. That's what engages the contactor. You may have a low pressure switch that is cutting power to the coil.