Cooling fan running to soon

[89blackvette]

I have 1989 Vette that has a fan problem, perhaps you guys can help. Cooling fan comes on at 124 (gauge display) degrees with AC off. Turning AC on makes no difference. My scanner says temp is 242 when engine is stone cold and fan starts at 248 (scanner display) when started. Scanner also shows fan request is on when fan is running and off when it is nit running. I have replaced the temperature sensor in front just under the throttle body with same results. Gauge temperature seems to be correct. Scanner says EPROM is 3291, what is that? Just do not want to work battery, alternator and fan motor more than necessary. AC blows cold and appeares to have never been tampered with. Could it possibly be the AC fan switch that turns on fan on AC is on? Thanks for your time.

Mike

 

[89blackvette]

Thanks for the help Guys. It is obviously the AC fan switch. Finally found it in FSM and disconnected it. Fan then runs off ECM signal as it should. Guess I will have to find one somewhere and go ahead and have AC converted to new refrigent.

 

[gmjunkie]

Thanks for the help Guys. It is obviously the AC fan switch. Finally found it in FSM and disconnected it. Fan then runs off ECM signal as it should. Guess I will have to find one somewhere and go ahead and have AC converted to new refrigent.

See what a great tool a FSM is!!
Is the analog gauge in sync with the digital gauge??
If not,It's a possibility that the temp sensor between #6-8 in the head is faulty!

 

[89blackvette]

It is 89 with digital gague only. Number 6 is on right side of engine and 7 is on left side? There is a sensor between 1 & 3 and a sensor between 6 & 8. I have replaced one between 1 & 3. I thought one on Right side was gague sensor, one on left is aux fan sensor and one in front is ECM sensor. Is that all correct? Now what? Thanks for your time.

 

[Schrade]

My scanner says temp is 242 when engine is stone cold

Good diagnostic testing! Most would have bought a pair of new fan relays by now, a new ECM, battery, fuel pump, air freshener, etc., ... :eyerole

If that [faulty] 242/cold signal is constant, and not intermittent, the source of that signal should be easily traceable. And I bet it is the source of the problem...

Yes - 6 is on passenger side and 7 is on driver side. I think he meant the sensor that's between 6 and 8.

 

[gmjunkie]

I think he meant the sensor that's between 6 and 8.

Yes,Thats the one I meant! Thats the one that controls the cooling fans on most later C4's,I even went back and checked my book for 89!

 

[ecss]

It is 89 with digital gauge only. Number 6 is on right side of engine and 7 is on left side? There is a sensor between 1 & 3 and a sensor between 6 & 8. I have replaced one between 1 & 3. I thought one on Right side was gauge sensor, one on left is aux fan sensor and one in front is ECM sensor. Is that all correct? Now what? Thanks for your time.

The single wire temperature switch screwed into the head between the 1 and 3 spark plug turns on the Auxiliary cooling fan that's mounted on the front of the AC condenser. That fan was optional and is not ECM controlled.

The temperature single wire sensor for the dash cluster gauge is screwed into the head between spark plug 6 and 8.

The ECT sensor which uses two wires is screwed into the front edge of the intake manifold and is what the ECM uses to determine when to turn on the main fan which is mounted on the engine side of the radiator.

The ECM will also turn on the main fan when the AC high side pressure reaches a certain pressure.

Your scanner temperature readings should come from the ECT.

 

[vetteoz]

It is obviously the AC fan switch. Finally found it in FSM and disconnected it. Fan then runs off ECM signal as it should.

Something is not right.
When the A/c turns on ,the pressure switch goes open sending a signal to the ECM commanding the main fan. If you remove the A/c system or unplug the pressure switch you have to jumper it to stop the fans from running all the time.