Product review (3 stars): Beware of load limits
Sensing current for the GA50 is 4.0 amps which seems acceptable.  If your blower draws less than that, loop the common wire from your blower motor (usually the white one) through the bracket twice.  The problem with this unit is the load rating.  Minimum load is 0.12 amps, which again seems acceptable, but max load rating is 0.42 amps, which seems way too low.  If the load rating was advertised, I would have never purchased it.  My humidifier has a 0.5 amp transformer, which probably explains why my relay is now stuck in the closed position after running it for several hours.  These relays should handle up to a 1.2 amp load if they are to be used with larger humidifiers.