Things are always changing in SJU these days. I just got an email from Cape Air stating that starting tomorrow (March 3), Cape Air's departures are moving to Gate C23. Here is the email:

Change is in the air at the Luis Muñoz Marín International Airport in San Juan! Here's what you need to know before you go...
Departures from SJU
Effective Tuesday, March 3, 2015, Cape Air's departure gate will be moving to Gate C23.
For customers who are originating in San Juan, please check in at the Cape Air ticket counter located in Terminal A. After check in, please proceed to the gate through one of two security checkpoints – the checkpoint at Terminal A or the centralized checkpoint at Terminal B. Please allow yourself adequate time when checking in for your flight.
For customers who are connecting from another airline and do not have luggage to claim, you may go directly to gate C23 to check in with a Cape Air representative.
Arrivals at SJU
If you are arriving from St. Thomas or St. Croix, you will arrive at gate C23. Checked luggage can be retrieved at Carousel #2.
If you are traveling from Tortola, Virgin Gorda, Nevis or Anguilla, you will arrive at gate C22 or C25, and will be taken directly to Immigration.
Passengers arriving from Mayagüez, Vieques or Culebra will be taken directly to the baggage claim area at Carousel #8.