Cooling fan not coming on

[Billholtzman]

My cooling fan on my 1978 Spider is not coming on.
This all started when I unplugged the fan when running (don't know what I was thinking.) I can hook up a battery charger to the fan and see it run, so I know it works. I know it is not the temp sending unit because I replaced that a year ago.
What could this be?
Thanks,
Bill in Maryland

[aj81spider]

Check the fuse. You may have blown it when pulling the connector off with power on.

[DieselSpider]

Also put an ohm meter on the sensor. The wires going into the epoxy on the radiator mounted sensor of the 78 are very delicate and are prone to breaking just below the surface of the epoxy.

I added a manual emergency switch that I use when I want the cooling fan to come on early when I anticipate a long stop so you could just jumper the leads going to the stat mounted on the bottom of the radiator to manually switch the fan on and verify that its the stat no longer having a good connection that's the issue.

[baltobernie]

Have you done any other work on the cooling system? Trapped air is often the culprit of the problem you describe. A cheap Harbor Freight infrared thermometer should be in every Spider's tool kit. This and a basic VOM are the best $15 you'll spend on your car.

[TX82FIAT]

When you unplugged the connection how dirty was it. Try cleaning the connection point so you know you have good continuity. A little dirt/corrosion in an Italian switch goes a long way to increase already feeble current flow.

[gchocevar]

Hi,

My fan on my 79 always worked until last month. I let the car warm up until the needle was in the hot range. I started moving the wires on the in-line connector, about a foot from the temp sender on the radiator. Behold, I could turn the fan on and off just by twisting the wires into the molded connector. I replaced the connector. Problem solved.

Good luck,
Greg

[Billholtzman]

Thank you everybody for responding so swiftly. Over the past day I have done what you all said and still nothing. I bled all the air out if the cooling system from the metal T piece, and from the other plastic T piece I installed on the heater hose going into the head. I cleaned my connections, and I jiggled the wires when the fan should be on, I put in the correct 16amp fuse, and still nothing.
Thanks,
Bill in MD

[DieselSpider]

And when you unplugged the wires from the thermal switch on the bottom of the radiator and manually jumpered it to bypass it what happened? Did you hear a relay click, fan turn on, etc? If you check with a volt meter on one of the leads going to it one if them should read 12 volts between it and the frame/ground. Don't presume that the switch, wiring harness or connector did not get physically damaged when you unplugged it under load especially if you used the OEM switch that goes on the bottom of the radiator of a 78 as they are notoriously fragile.

[aj81spider]

Here's how I would proceed to determine if it is an electrical problem:

1.) Pull the connector off the thermal switch at the bottom of the radiator. Short the connector with a short piece of wire (the connector on the car side, not the radiator side. If the fan comes on then your problem is the switch. Replace it. If the switch is good, then your problem is not electrical and find out why your cooling system is not distributing hot water to the switch.

2.) If the fan doesn't come on, pull the connector to the fan and measure the car side with a voltmeter. If there is 12 volts there then either your fan is bad or your connector is not making connection (and you said you tested the fan, so it would probably be the connector). If there is no voltage there you have a wire or fuse problem somewhere.

3.) Get the wiring diagram (you can find a 1978 wiring diagram at artigue.com, or PM me your email address and I can send you one). Check the voltage at various points along the circuit (fuse box, ignition switch) etc - until you find a point where there is voltage. Between that point and the previous point you measured will be the problem. It is far more likely the problem is a connector, fuse, or switch than a broken wire, so check those first.

The circuit is pretty simple, so finding the issue should not be that hard if it is electrical.

[colblu44]

I have a new cooling fan relay switch and don't know where to connect the two leads. Wires on old one go nowhere. I assume it plugs into the relay, but where is that on a 1981 Spider 2000 with EFI? Can't find a pic anywhere online. Thanks.

[RRoller123]