Hi,
So before I start, the car is a 1987 Pontiac Trans AM 305 TPI/AUTO with Vin code "F". I understand from what I have read (and maybe I am wrong), 1987 was a special year for cooling fan setup. This car is a low mileage completely stock car. I did try a search here as well as the internet but it seems I can't find anything specific to my problem with this year car, and engine.

So, my issue is the Cooling fans never come on. It can overheat and they won't turn on. I know the coolant temp switch (under the throttle body) is working because my SNAP ON MT 2500 scanner shows it with correct temp, along with the gauge in the car.

I am stumped because (and I realize there are 2 circuits to make the fans turn on), if I pull the connector to the AC pressure switch on the high side line, the DRIVER FAN will come on. If it plug it back into the pressure switch, the fan turns off. The PASSENGER motor never turns on under any circumstance however I have spun the fan electronically (applied power) and it works.

I keep hearing about a FAN SWITCH but I don't know where that is on this year, this engine. The only thing I see on either the passenger or driver head is the temp gauge (driver side with green wire going to). Is that the fan switch as well? If i disconnect the green wire, the coolant gauge stops working so I assume the switch and wire are good. Is there a FAN switch for this 1987 model year and engine? If so, where is it?

I have also swapped the FAN relays and that has not done anything but I assume if I pulled the AC pressure switch connector and the DRIVER fan turned on, the wiring and relay to that fan is good. If that is not good logic, please tell me.

Really stumped so any advice from anyone would be appreciated.

Thanks for any help........

 

Yeah they changed up the fan circuitry quite a few times and for different engines too, not always easy to "assume" that what you're "heard" or "read" will apply to your car.

Look in the same hole that the gauge sending unit is in, except the pass side head. Will be between the #6 & #8 spark plugs. If you have a fan switch that's where it will be. Should have either a grn w wht stripe or a grey wire.

 

Yep. You are right. Thanks. Not sure how I missed that but it seems buried behind the starter. Looks like a 2 wire connector. Should I assume if I unplug that connector and jumper it the fan should turn on? If that happened, would that mean the switch is bad? Thanks for your help.

 

Doesn't sound right butt I don't know for sure. Those are generally a 1-wire connector, and the switch goes into the head, not the block; between those 2 spark plugs.

A photo might help. Wire colors might help. Looking it up at Autozone or Rockauto or GMPartsDirect and matching what they show to what you have might help.

 

The one in the block is the knock sensor. The fan switch is, like Sofa said, between the #6 & #8 spark plugs...

 

OK some updates....

Its pretty hard for me to get under the car but managed to do so today....I did find the "one" wire plug going to the Fan control switch in the head between the #6 and #8 plugs just as you said. So I disconnected it and grounded it and the PASSENGER fan spun (not the driver). Is it just supposed to spin the PASSENGER fan? or both?

So I am now even more confused as I had explained in the earlier post the only way the DRIVER fan comes on is when I pull the A/C high pressure switch connector.

So , should I assume, that if I grounded the fan control switch and the PASSENGER fan spun and when I unplug the A/C pressure switch connector the DRIVER fan spun that all my wiring and relays are good? If not, where should I look next? If so, why isn't the driver fan ever coming on even when it is hitting 235 degrees? What controls the DRIVER fan other than the A/C high pressure switch.? From my understanding its the ECM that commands it on. So is it possible a bad computer?
Thanks for any next steps.....

 

Most people just eventually rewire the fans so that it’s not a two stage or anything. Just that both fans come on when either the PCM commands it or the sender in the head trips at like 225° as a backup.

I know there are harness diagrams for that somewhere on these boards

 

Thanks but would like to make it work from original design...just trying to figure it out why that driver fan doesn't spin when everything looks correct.....

 

Just read an article here:

https://www.justanswer.com/car/0skcx...5-tpi-car.html

So now I am curious, does anyone know if the primary fan (Driver fan) is dependent on the fan switch working properly to turn on? Everything I have read said the Fan switch (in the passenger head) only controls/matters to the Passenger fan and has nothing to do with the ECM. Only remaining guess is if the fan switch is bad, perhaps it is hindering the Driver fan from coming on. Can anyone confirm that for an 87 car ?

Thanks.

 

The passenger fan is supposed to come on when the A/C is on. The driver side should come on when it gets too warm. On my 1990 IROC with the 305 the relay for that is on the drivers side. Look at your relays and see if one of them is charred. I believe it was the middle relay on the fire wall on the drivers side. (that is the one that looks the newest). Also do a search on this subject and I talked about it before.
Wootdog.

 

Thanks for reply but the 87 is a different setup than other years. The A/C spins the Driver fan, not passenger. Also early in my thread I confirmed relays and wiring.