[adestefan]

You don't want to monitor if it's blowing, since the unit could still be blowing air, but not cold air. Instead, monitor the temperature coming out of/in the the duct. The temperature change in the duct will allow for a page just as fast as monitoring the flow.

This will also allow you to monitor things such as the delta of the air coming out of the duct vs the ambient temperature vs the air going into the return. With this data you can create significant savings by moving ducts or equipment since you're probably wasting a lot of good, cold air going into the return.

It will also be cheaper. A lot cheaper.

[protomyth]

I've got temp sensors in the mix, but I can have the same temp near the duct for a bit after the blowing stops. I also want to make sure the blower stays at the same rate and isn't sputtering.

[joezydeco]

How about monitoring the compressor itself and not it's output? Maybe a hall-effect sensor attached to the outside of the unit could work?

[protomyth]

I cannot make alterations to the environment or put stuff outside, nice thought though.

// ND -40F in winter - not allowed to cut holes in wall and no extra power outside.