First of all you are over complicating things.
1. If you are running Co2 then you can have temps in the mid-high 80s instead of the 70's.....thats one major benefit to Co2.
This will reduce the need for cooling the space and reduce the time your a/c needs to run.
2. The exhaust fan on a portable a/c does not begin to compare to the cubic volume of most grow rooms therefor you will not
be exchanging the enriched air as often as you may think. It will not be able to draw out the Co2 as quickly as you are generating it.
My recommendation is to plug the a/c into a CAP-Dne Thermostat. This is a plug in thermostat that the a/c will plug into and is much more accurate than the onboard equipment that comes with the a/c. Let the a/c run whenever it needs to in order to maintain desired temps, vent the exhaust and be done with it.
Now if you want to get fancy then install a greenhouse master controller that cycles off Co2 whenever A/C or other exhaust appliances run. Custon Automated Products is a candy store for this kind of equipment. a.k.a. CAP.