We have a 410A duroguard Air Handler that needs to be converted to R22

You do not convert unless it was certified at the factory at the time of manufacturer that it could be used with R-410A refrigerant. R-410A runs at a higher pressure than R-22 and that is the problem.

Are you saying you have a 410A airhandler now, but a 22 condenser unit outside? You can use 410 rated evap coils on a 22 system as long as you use the correct metering device. Im assuming this is a air handler replacement while keeping the old condenser unit?