The relays shown here are SPST (Single Pole, Single Throw), which will be identified as having a middle 87b spade (or possibly no middle spade at all).  This type of relay provides power to the 87b pin whenever there is power to the 87 (when relay is "on").  This way the 87b may be used as an extra power output when the relay is being used.

If you have a relay with an 87a in the middle spot, it is a SPDT (Single Pole, Double Throw) relay, sometimes called a "changeover relay."   This type of relay will work for this application, however be aware of this:  The 87a pin is constant hot anytime the relay is "OFF," (as long as power is connected to pin 30).  This means a fan will run any time pin 30 is connected to 12V, but will then switch OFF when the relay triggers to "on." (when power is applied to Signal pin 85 and Ground pin 86 is complete.

This diagram works well if you only wish to add a single fan to the front of your A/C condenser.  It will not come on at a particular temperature, but only when the A/C is turned on.