I have a goodman furnace 98% efficient it works fine on heat but when I run the ac unit it will run fine for an hour or three but then it will start stoping and starting the blower motor I have changed the transformer the blower motor the door switch anyone have any idea why it does this any help would be greatly appreciated

Sounds like you have changed a lot of parts unneeded, try bypassing the thermostat by removing the r - y - g wires, twist them together,, does your equipment still have the same problem? If not ,it's a bad tstat, if prob. Still there ,you have proven the tstat is OK and must look farther,, let us know