I have a strange overheating problem on my Lancer. When idling for some time with the A/C off it operates at normal temperature. With the A/C on idling for less than 1 hr it operates at normal temperatures. When driving around with the A/C off it doesn't overheat. After driving around for about 20-30 minutes with the A/C on and then stopping the car begins to overheat. When it is overheating if I shut the A/C off it starts cooling down. Both fans come on when the A/C is on, but the driver side fan doesn't appear to come on when idling or when driving.

Does anyone know what could be causing this behavior? And how do i fix it...

 

My initial guess would be the fan is either wired backwards, or the fan could be installed backwards.

Why do you mention the driver side fan? Isn't there only 1 fan on the Lancer? It's been a while since I looked at it, so maybe I'm mistaking the Lancer setup with a Honda setup.

If you want to troubleshoot fans coming ON and OFF, you could temporarly wire a small light bulb inline with the power feed to the fans. 1 per fan if there is indeed two fans. When the light turns ON, you'd know the fan just turned on. If you use a wire long enough you could set the lights inside the car so you don't have to pop the hood. You'd get the info while driving.

Edit:
I just looked at the service manual, and there is indeed two fans. So yeah, I'd wire a light bulb on each fan and go around town. Since it's only for troubleshooting, it doesn't need to be pretty, it just needs to be functionnal. So don't bother routing the wires through the firewall and all. Just have it exit through the gap between the hood and the body, and bring it inside the car through the window. Once you're done, just remove everything.