I have a Goodman system and the a/c unit kicks on but sometimes the blower unit in the air handler does not. I replaced the thermostat and everything works as it should but still same problem. Where is the relay located for the blower unit?

It will be located in the electrical compartment of the air handler. With the power off to the air handler spin the blower wheel to make sure the motor feels free. Does it seem like the motor has a hard time starting?

The fan motor runs freely. The fans runs properly in the "on" position but when in the "auto" position it does not always kick in. I can cut the system of and wait a few minutes and cut it back on and it will work for a time. I took the cover off the handler and the diagram shows a "BTDR" relay... is this the one I am looking for?

In air conditioning it uses the blower relay the same when the fan switch is on auto and "ON" Check your thermostat connections and make sure the Green wire is making a good connection. It may be the thermostat is not always sending 24 volts to the "G" terminal when the call for A/C is made. I don't think the relay is the problem. Check the low voltage connections on the air handler it's self, it may be a loose wire nut or something.