Volvo: Fan will not turn on at warm up, engine coolant, proper test

Question
Hello Ray,

My fan will not turn on unless I direct wire it from the relay- middle ground wire to the battery. A mechanic said that it might be the Ecu or wire problem. I hope its not the Ecu(Too expensive!!) This is causing the Engine to overheat and the antifreeze to rise at the resevour, when I'm like stuck at a traffic. I'm dying to know the best way to fix this. I'm thinking it's the Engine Coolant Temperatur Switch. What are your thoughts on this?  

Answer
Gene,
You should have a two speed fan, perhaps only the high speed is working and not low speed. Low speed usually comes on first. The proper test is with the VST if your car is 96 or newer. (Volvo Scan Tool) With the scanner hooked up it will test the high and low speed. You may have a relay that low speed is out on. Check the wiring back to the control unit maybe the signal is not getting to the relay.