I have recently purchased my 1999 k2500, the hvac blower would only work on high so i assumed the resistor. I changed resistor, did not fix problem. I then replaced control board assembly this worked for short time then it quit working intermittedly completely . I changed the motor next then it was working only on high but not always . Next i changed the relay, worked again sometimes but would still not work all the time. I changed the resister again because when it did work it was only on high. I changed the relay a second time and didn't help. With test light on relay i have my power to red wire and off and on wire to purple which goes to blower. Any suggestions? Can you tell me what activates the relay to power the blower from there?