Replace the fan control board at night work good during the hot time of the day it take 5 min or longer down good what else would cause this

I have a Lennox XC 21 unit and about two years ago, the motor run capacitor went. I brought the bulged out one to my local warehouse and they sold me the replacement, a TRCF 80. This week I decided to get a spare one just in case this one goes. I ordered the EXACT same one. The item arrived today and when I opened it, I noticed instead of having THREE prongs on top, it only as two. So, my question is two fold. 1) Why two prongs instead of three, which leads to question two. 2) There are only TWO wires connected to the capacitor inside the unit. NOTE: There are three wires inside my unit, red, yellow and blue. Just the red and yellow are connected. If it matters, the unit runs perfectly. Thanks!