hi,
I understand that you require *1000 for the final circuit when using the force sensor, ie: 100K0 resistor.
I suggest a lower Rg value in order to check the AD623.
The sensor is a bridge configuration, how are you powering the sensor? What are the voltages?
The REF pin is used to inject a correction voltage into the AD623 that will cancel any 'offset in the output' caused by different power/ground voltages at the inputs of the AD623.
As the datasheet states, the REF voltage can be +/-Vsupply.
You have not answered my question regarding the output voltage?
If you want to use the REF pin, I would suggest that you connect a pot [100k], between +5V and -5V, with the wiper connected to REF via a 10K0 resistor.
By adjusting the REF pot, you should be able to set the AD623 output to zero.
I suspect that at the moment its at 0V or +5V without the pot.[ with Rg=100K0, a Gain of 1000]
EDIT: look at Fig 49 of the datasheet, for how to use the REF pin voltage.
If you give me answers I maybe able to help.