had the aux fan wired direct and tuned to come on earlier....noticed the other night gjoing through a drive through with a/c in s fl...a bit of a vibration in the nose.....tried it today, doesn't come on with a/c or manual switch....in reaching down there with the radiator fan on, I can feel air blowing through the condenser from the radiaton fan.....idled it quite a while with a/c on and only radiator fan on....couldn't get it over 180 sitting in the driveway...very hot s fl day....now i'd like to know three things.


1 do I even need the aux fan?

2. is there a quick power test/?..groundng didn't start it up

3 is there a better aftermarket fan to replace it....or a upgrade to the stock radiator fan??? thanks in advance Paul

 

Hi
Below is the wiring diagram for the 85 corvette from my shop manual, you can see the ecm operates the main fan via the temp sender in the inlet manifold base above the water pump. It may be different to the dash readout.


The auxillary "booster fan" is opperated by the temp switch in the head (passenger side but i have seen some on the other side)
Grounding the plug that connects to the temp sender will start the auxillary fan right away, the switch grounds the plug.

On vettes without the auxillary fans the switch in the head is used as a overide if the ecm fails to run the cooling fan.

So if the auxillary fan does not start when grounding the wire /plug check the auxillary cooling fan relay.

 

thanks, I have the fsm...I originally grounded the green wire going into the relay to manually work it....that no longer works ..i''m assuming there should be power at one of those sockets on the plug....right"???

would grounding the cooland wire be a better test...?

 

Check the 12 volts from the auxillary cooling fan fuse to terminal C, then check the 12 volts from the fusable link is there on terminal D.
The green wire grounds the relay to operate it, it may just be a bad relay or the contacts burnt at the switch between D and A.

So check you have 12 volts at C (dark blue) and D (red) if you do then the relay is bad OR the fan is burnt out or jammed by something but you know what to look for then.

The main cooling fan is activated by the temp the ecm sees AND the a/c pressure switch. (it is the small round plug on the pipe) and it has another plug with just spade terminals that is the high pressure safety that will stop the a/c compressor.

Remove the small plug depress the clip and when it is removed the cooling fan will run continually as the ecm will turn the fan on while the contact is open.

The Auxillary fan only comes on when the engine temp is at 235 0r 239
and the switch in the head grounds the relay to run the auxillary fan.
Nothing to do with a/c that is via the cooling fan.

The small round pressure switch may need to be replaced if the colling fan does not activate and compressor turns of via the high pressure safety.

This is a link to one i got on ebay recently, to see what they look like the a/c fan request pressure switch.


http://www.ebay.com/itm/ACDelco-15-2351-Radiator-Fan-Switch-/131228668736?pt=Motors_Car_Truck_Parts_Accessories&hash=item1e8dd69340#ht_0wt_0

 

thanks so much, i'll be checking it all tomorrow. while I was d0wn there checking the aux fan, i could feel a pretty good flow thru the condenser from the rad fan.....if the aux fan is shot, do I really need it""?

 

It was an option the heavy duty cooling, a lot of vettes do not have it but it is a great backup in case the main cooling fan stops working. You will still be able to drive it home with the Auxillary fan.
(i have done that when the cooling fan motor died)

The cooling fan is disabled at highway speed, unless the a/c is running and the pressure switch asks for the cooling fan.
but you need the cooling fan at stop and start traffic.

The auxillary fans are pretty cheap, and yes the auxillary fan does get used in the summer with a/c on to keep the temps down.
Depends on how hot it gets where you live.

 

I live in s fl...it's hot enough...i'll fix it or replace it...

 

here's the update....the aux fan sensor was bad....rather than replace it, I wired it in to manual switch.....I prefer turning it on when I need it anyway....with a new radiator and 160 t stat it rarely see's 200 with the a/c in traffic ...just want to be prepared....thanks for the help....