Is there such an animal, and if so, where is it located?

My compressor does not engage at all. The A/C was fine last time I used it a few months ago, but now when I turn it on, the compressor won't lick in, and the system blows outside air only.

Thanks

 

Your higher mileage 08 vehicle is now 12 years old.
Most A/c lines start to deteriorate and seals start leaking refrigerant by now. Best to see if it is still up to "charge" before going after electricals. And I'm pretty sure that there is no plug in relay, but controlled thru the BCM and TIPM/FUSE PANEL under the hood.