I see.

Well, 12,000 BTU equals 1 tonne of cooling. So, off the top of my head, each tonne of cooling (at 240V) requires 10A ampacity. That whould mean that at 120V, you should require a 20A circuit. This allows for in-rush during start-up, which can be high for a compressor under pressure, as much as 6 times the FLA (full load amps) rating of the compressor. This could be 12 amps for a unit that size, which is 72 amps. Your inverter may also have trouble with inductive loads, I've seen it before. Your cord end will be 15A rated, as that's what is on the inverter. But, it's not the first time that manufacturers put 15A cord ends on items that draw 15 amps continuously (even though in Canada, CSA requires no more than 80% loading, so that means 12A max). Look at 1500W hairdryers used on residential circuits with 1200w max loading.

My original suggestion is reinforced. Get a larger inverter.

I knew at start-up there was a significantly higher draw, but I didn't realize 6xs.
But again, it only happens once in a while (1 out of 10 times). Once the air conditioner is running, everything is fine. It is something I can live with. I just thought if there was an easy fix, I would employ it now while I am finishing up that area. To shut off and restart the inverter is a flick of a switch in the drivers compartment. No big deal. I really want to get moving on finishing the audio portion of the car. I have been working on this car for 3 years, I REALLY want to get it done this year.
Thank you VERY much for your input :)

Evil, pick yourself up an a/c hard start kit. It is a start capacitor and start relay packaged in one. Get one that is rated for 1-3 tons or 1-3hp (same kit depending on the manufacturer). You can get one from anybody that sells hvac parts or equipment. You simply wire the kit (two leads) in parallel with the compressor's run capacitor, ie: one lead to "c" (common terminal) and the other lead to the "herm" terminal (the compressor terminal) on the run cap. This will help the compressor to start a little easier and reduce your FLA upon start up. All this does is give the compressor a little boost while it is still on the start winding, then once the compressor's run winding is energized the relay takes the start cap back out of the circuit. These work well and I have used them many times for several different reasons. I am willing to bet that this will cure your issue once and for all.

The Wizard

Sounds perfect. Thx