I have done alot of research on this, and cannot understand what is happening. To the best of my knowledge my 94 lt1 has two coolent temp sending units. One goes to the analog gauge in the dash, the other to the ecm and is displayed in the digital portion of the dash which is the controling factor as to when the fans turn on. Both are reading correct temps. However after about 8 seconds of running BOTH cooling fans turn on. The engine isnt even over 100 deg at that point on both gauges! They never shut off. Both fan relays are functioning. Also the A/c comperssor will not engage I dont know if these two things are related but I need to fix both problems. Any advise on the subject would be very appreciated! Thank you.

 

possibly you have a bad a\c compressor switch? i know when you turn on the a\c the fans come on, no matter what temp the coolant is.

 

Actually, 1 is a sending unit and the other is a sensor for fuel injection control, a matter of semantics I know, but I'll try to look at wiring diagram on Monday. If I am not mistaken, compressor is ECM controlled. Have you tried to put voltage to the compressor to see if the clutch engages? Have you put a/c gauges on to see if you have any freon in ther system? Risidual pressure on hi and low sides should be around 80 lbs when outside temp is in the 80's, cooler weather means lower risidual pressures. You have a compressor relay, you also have a cooling fan relay. ECM grounds relay for fan based on inputs it is looking at, such a/c request (did u turn on a/c at control head ), pressure readings from low side and high side switches. Like I said, lots of things to look at. First make sure your compressor clutch engages like I described earlier. Get back to me with results. [8D]