If I can stop thinking about Cindy Crawford I'll jump in.

I don't think ammonia is very flammable; dangerous, reactive, toxic, sure but I don't think it burns, but I've been wrong before.

My AC system is great. I knew about the early refrigeration systems that ran on ammonia but was not aware of units based on hydrocarbons (HC). It made me curious. So I went to the duracool site and the EPA site.

As others have commented a number of static systems run on HC. But the EPA bans the usage in non-static applications. Then I read some more and found a number of folks writing about how successful they have been in running their auto AC on HC.

I wondered a bit about having 18 oz of HC at ~ 15 atm under the hood. I've made some very simple calculations (tried not to screw them up) and concluded that 18 oz of butane (using that as the worst case example) in the AC system if it ignited would release the same amount of energy as burning about 1/6th of a gallon of gas.

Since 1/6th of a gallon of gas moves my car about 5 miles (on the highway, your mileage may differ ) I've decided that was a lot of energy and the consequences of a mistake are too great to make the thought of putting in an auto attractive.

Now, back to Cindy Crawford!