hello all I am the new guy, the one with the 88 that recently posted about the problem that when my A/C is on and the fan starts the coolant temp will go to the max at 160c and 290f... well today I give it a real look and found out that my sensor near the dip stick have 2 wires attached to it 1 green wire, and one black wire with a yellow stripe that it goes all the way to the fan relay the one located near the battery ,the relay has 4 wires - 1 green wire, 1 blue wire, 1 black wire and 1 red wire :confused: and the black wire that comes from the sensor is making contact like connected with the green wire from the relay. :confused: It does not look like factory at all .......why you think some body do that ??
for what reason ? what should I do ? I think that this is making the coolant temp to go up when the fan starts !! what you think becouse I am confused now and going :crazy: please help !!!! :(

 

My manual doesn't describe a second wire coming from the right side sensor to the relay near the battery. That right side sensor is the overtemp sensor that turns on the auxilliary fan mounted in front of the A/C condensor. My 89 only has one wire on that sensor. It's associated relay, if like my 89, is mounted on the left side of the cowling surrounding the radiator. The relay you found on the left side near the battery, probably mounted under the front of the brake master cylinder, is the overtemp sensor relay for the main fan mounted behind the radiator. It's overtemp control sensor is mounted in the left head between the #1 and #3 cylinder. You should see the wire running to it from the wheel well area. I have a suspicion someone ran a jumper from the aux fan's sensor on the right side over to the main fan's relay on the left side to control both fans at the same time. If removing this jumper wire fixes the problem and you're sure the coolant temp is within reason then I'd remove the wire and forget about it.

You can ground either sensor wire, with the ignition switch on, and it's associated fan should run. Maybe there's a problem somewhere, like a bad relay, that caused someone to add this jumper wire. I'm baffled why this jumper, if that's what it is, would cause a false high temp reading unless maybe it's connected to the wrong point on the relay.

You might want to buy a manual to help isolate this and other problems you'll find later on. The Haynes manual is readily available at most parts stores and covers this area fairly well, though it doesn't have complete wiring diagrams. Better manuals can be found online or check with the local Chevy dealer.

Good luck!! :flag

 

The thing is that I dont have another fan ,,I only have one fan mounted in front of the engine that is the main fan only !!
should I disconect the black wire from the sensor and see what heppens ??
thank you

 

UPDATE -- I have just checked and took the black wire of the sensor ( it was connected with the green wire ) and the coolant temp stayed Lo , but now the fan only turns when the A/C is on ,with the A/C off it won`t even come on even at 210 f coolant temp it stayed off :confused: ...then I tried something ,I tried to ground that black wire that was on the sensor and wala the fan started ,,,whats wrong with all this, what sould I replace to go back to normal ?? please help :cry

 

Any cuts or splices in the wiring? i.e. Has anybody messed w/ the stock wiring?

 

NO cuts or splice at all, just a wire from the coolant sensor to the relay the one located under the brake master cylinder and it is connected with a conector I have never seen one like it ,it`s a piece of plastic with 2 metal pins one goes in the black wire and one goes in to the green wire from the relay ,,,,,,if I replace that relay should it be fixed ? :confused:

 

Sensor near the dipstick is for the Temp Gauge and should just have a green wire. ECM commands the main fan to come on, a/c off, at 226 F. Temperature input is from the Coolant Temp Sensor at the front of the intake manifold not the gauge. With a/c on, ECM commands the main fan to come on when high side pressure switch closes, about 240 psi. Turns off fan when high side drops to 170 - 190 psi. At the Relay, Green wire is signal from ECM which applies a ground to energize the Relay. Blue wire is ignition voltage and when grounded by ECM signal (green wire), relay energizes which then applies battery voltage, red wire, through the black wire which is the hot lead to the fan. Fan is externally grounded. If someone wired the ECM lead (green wire at Relay) to a fixed ground, my guess is that they wanted the fan on at all times. If fan isn't coming on at 226 with the a/c off, check connection at coolant temp sensor, front of intake. Might need a new sensor also. ECM and Relay appear to be ok since fan comes on with a/c.

 

Thank you for all of you that replyed at my qustions ,yesterday my fan came on at 225F and I was very happy that everthing is normal thank you all and :cheers: