How cold is a “freeze spray” – the sort for freezing pipes instead of draining a system?
Forget the spray, get some liquid nitrogen, or propane gas that you can deliver as a liquid. Short of a performance test of just the sensor in the environment you want to test it in, you are going to have a lot of trouble getting the results that you want. Try putting a sample arrangement inside a freezer and use that to arrive at the temperature that you want to achieve. The process that you have described sounds like it is fraught with variables that will only lead to inconclusive results, and a lot of frustration. To be accurate, what ever you do to test these sensors has to be repeatable. Your set up doesn’t sound like anything, except frustration and variable readings, is going to be repeatable.
