2003 civic EX 1.7L automatic
Hello, I am trying to help my friend with a really weird cooling fan issue. The cooling fans were not coming on and while sitting in traffic the car would overheat. Temperature is normal while moving. My first thought was either relay or fan switch. I pulled the connector from the fan switch sensor and shorted it while the key was in the on position and this caused both fans to come on correctly, so I thought replacing the switch would fix the issue. Proceeded to go to an autozone and get a new switch, however while sitting parked and the temperature rising well above the middle, the fans still did not kick on. However, we found that with the cabin fan switch (blower) turned on to the lowest setting (or anything above off) WITHOUT the A/C on, the fan started working normally. (Turned on while heat was high, and cut off when heat went back down) When turning the A/C on, the fans continue to turn as they would while using A/C and A/C works fine. Also tested shorting the fan switch connection again, which turns the cooling fans on like before.
So, what is going on with only getting the automatic thermostatic fan behavior when the cabin fans are on? Because shorting the switch still works, it is possible that we got a bad replacement part from the auto parts store? Obviously he can just drive the car with the fan on the lowest setting for the time being, but it is really bugging me what the actual problem is.
Thanks for reading!