LT Texan

I'm trying to figure out a problem and best to toss it out for comments here.

I have replaced my belt fan with two 12inch electrics and wired these to the jump post via a relay and the radiator thermo switch. Eliminating the aircon fan from that switch. So now the aircon fan only switches on via the aircon temp switch.

The radiator fans are having a bit of a problem keeping things cool, so I got the idea to hook the aircon fan back up with the radiator switch in addition to the radiator fans. So all three will run with hot water temp.

Here's the problem....

The hot relay wire for the aircon fan is 12V with the key on in any position. With the key off, the hot wire is grounded???!!!??!!!??!!

So this causes the hot wire from the radiator fans' relay to kick on making the circuit by grounding via the condenser fan relay's hot wire?????

Looking at the current flow, I don't get it.

Any ideas?

stolarzj

If the two fans are having a hard time keeping up, try reversing the rotation of the fans, you may be turning them in the wrong direction. You shouldn't need three fans.

Also if you used the stock one temp thermo switch it's temp setting is designed to come on when it's already getting to hot. You really need a two way switch with a lower temp then a higher temp to kick on the other fan. You might even get away with running one of the dual fans at low temp setting and then kick on the second at high temp setting.

LT Texan

I'm using a lower temp switch already.

It's really odd.

The aircon fan relay hot wire to the thermo switch is 12V with the ignition on and GROUND with the ignition off.

stolarzj

Try reversing your fans and see if the temp changes.

LT Texan

Here're the two 12 inch fans. Both Proform 1200cfm's at 7 amps.

The 14" in the front is also Proform 1650 cfm at 8 amps.

LT Texan

these are pullers. when on, they turn cw (like the instructions say, when looking at the front) and air blows out the back.

Alan

Since your new fan configuratiion is aftermarket you will probably have to explain what you did better to get any helpful answers.

You should still be able to get it to work anyway - maybe just use 2 relays in parallel for your fans...

Alan

WallyP

Dan,

To get back to your original question....

The original operation of the electric cooling fan is thru a single relay. The coil of the relay has power from the X bus, which is basically ignition switched power, so the relay coil is hot any time that the ignition switch is on. When either the radiator temp switch or the refrigerant temp switch is activated by high temp, the other side of the relay coil is grounded, causing the relay to operate, applying battery power to the fan motor thru the relay contacts.

If you check the power side of any of the ignition-switched devices, you will see what appears to be a ground when the ignition switch is off. This is because all of the ignition-switched devices are basically hooked together, so what you are seeing is the total resistance of several devices hooked in parallel.

From your description, your problem is that you apparently have the relay coil for the radiator temp switch hooked to the 30 bus (unswitched battery power). Hook it to the same voltage source as the refrigerant temp switch, and you will have no problem.

LT Texan

yep.

The old mechanical fan wasn't cooling so great, so I got the idea to eliminate it with an electric fan.

First, let's get this out of the way. I'm always trying things myself because I like to and because I figure I'll save money (never do).

Since I had a pretty weak alternator (before the Delco), I wanted a 16" fan with low amp draw. I found one at Summit Racing (Proform) that was rated 2100fm and 8 amps. I also got a new temp switch for the radiator with a lower on temp.

To wire it up, I wired in a relay and fuses from the jump post. To turn on the relay, I wired to the radiator temp switch. I also disconnected the stock aircon condenser fan from that switch.

So I ended up with a radiator fan switched by the radiator temp switch that ran whenever the radiator temp switch was closed.

And a aircon condenser fan that worked when the aircon temp switch was closed and the key in any "on" position.

Last summer all seemed fine, But I didn't drive much, only on nice days.

This summer, on really hot days, the 16" fan wasn't cutting it.

So I bought the 2 12" fans described above.

These kept the temp gauge just past the 2nd white mark (2/3rds).

So I thought. Why not reconnect the aircon fan relay "hot" wire back to the radiator temp switch along with the dual radiator fans and see if that gets the temp back down below the second white line?

This is where I ran into trouble.

The + side wire of the aircon fan relay to the radiator temp switch is at 12V when the key is "on." When the key is off, this wire reads ground with my multi meter.

On the current flow diagram for the 1978, Part VII, I can see the aircon fan relay wire come from the fan relay to the radiator temp switch. The top of the fan relay (electromagnet side) is wired from a track marked "x" on the fuse/relay board (I don't understand what the x means).

i don't understand why the stock wiring from the aircon fan relay to the radiator temp switch would read 12v with the key on and "ground" with the key off.

It is the stock wiring that has me baffled.

Do the input side of the hot wires somehow switch to earth if the key is off?

Very odd.

And yes another temp gauge will do the trick, but I want only one.

(PS yes I have since read the thread on the Ford V6 dual radiator and shroud which would have been a much better attempt.)

LT Texan

Wow, I never would have thought that.

Thanks much.

James Bailey

The two puller fans ONLY cool the part of the radiator which they cover....so about half of your radiator gets none of the airflow. That is what shrouds are for they cause the air to flow over all the radiator so heat is exchanged on the entire surface area.

LT Texan

nice beating Mr Bailey.

WallyP

Agreed! That is why the pull-a-part Ford fans work so well.

One thing that is interesting - you want about half of the end of each blade exposed behind the shroud. The fans work better with both axial flow and centrifugal flow.

76FJ55

This is purely speculation, but I am guessing you are using a 3 post relay, and it is due to the design of the relay. It is a high current carrying relay so to increase life I am going to guess that it incorporates an anti arcing circuit. this circit will place a capacitor and resistor in parralel with the load contact. that way when the load contact is broken the capacitor will absorb the energy decreasing the arcing potential increasing the contact life. There may also be a discharge resistor and some other stuff in there I don't know all the particulars. The ground path you are seeing I would guess is back through the relay triggering coil across the anti-arcuing circuit and grounding through your primary fans windings. an easy way to test would be to disconnect the fans and see if the ground path goes away.

jpitman2

Note also that using the bottom temp sensor does not provide very good temp control with electric fans, compared to a sensor mounted at the top. One of our Oz guys has fitted a sensor in the top hose after having issues with the original location (track usage), and found the temps are much better controlled. I still have the old sensor in place, and with 2x11" SPAL fans in a shroud, have no trouble keeping temp under the second white line in 100F ambient with AC on. One fan is powered and switched by the original ac fan wiring, the second fan is powered/relayed from the jump post, but switched by the first fan's power. When I fit a top mounted sensor, I plan to use a 90/85C switch.
jp 83 EURO S AT 53k