kwkrat2

iTrader: (2)

I have installed a 2speed electric fan from a Ford Taurus in my 69 Camaro, and it seems to work fine, but when the fan is on start-up, it buzzes the relay and the fan starts off slow. I have had 3 failures of my 40amp relays(each different manufactures) already, and I can't afford to overheat the motor again.

I have the 2 relays wired through each other (low and high speed)using the ECM as the trigger ground. I see that there are a bunch of different ways and relay types to use for this setup.

What seems to be the best set-up(wiring and relay) to use? The fan works awesome and keeps the car extremely cool, even in the heat of summer, but it seems that the amp draw is way too much for the relays to handle.

I believe this is the set-up I have with the temp switch being the ECM.

Pop N Wood

iTrader: (1)

Put a voltmeter across the coils of the relay when it is buzzing (pins 85 to 86) and I can almost guarantee you will see a low voltage condition. I would guess either your 12V supply or your grounds aren't adequate.

When the relay is buzzing measure the voltage from the coil input (pin 85) and output (pin 86) to ground. If the input pin 85 volts are not within a couple of volts of the alternator output volts, then the issue is in the 12 v supply. If the ground pin has a high volts, then the ground isn't going through the temp switch right.

You have some heavy gauge wires. Problem could be a bad connection or you tapped the power off a bad point. Having pitted contacts in relay #1 could also be a problem. A bad engine ground could be a problem.

BTW, that 30 amp fuse might be marginal with the fan on high.

If you don't have a voltmeter grounding pin 85 of either relay straight to a good engine ground with a jumper wire is a good test of the grounding circuits. Running a jumper straight from the battery to the first relay is a good check of the supply line.

Rather than buy expensive relays just get some from the donor car you got the fan from.

kwkrat2

iTrader: (2)

The power supply and ground for the trigger of the relay are coming frfom the ECM? The ECM has 4 wires coming from it marked low speed fan + and -, high speed fan + and -. This is on the harness Speartech sent me. I called them and they said that is the trigger wires for the relay.
The fan has a ground directly to the frame of the car, and the power wire for the fan comes directly from the battery wich is about 10" from the relays.
If it is a low voltage signal from the ECM, how do you solve this?

74modified

Here is what works for me. If not using an ECM your temp switches would take the place of those inputs.

Tramminc

Can the computer (PCM) run both fans at the same time? or does the PCM output low ground open in the computer?
I'm planning to hook up 1 relay and fan (relays not connected) to each output.

74modified

The diagram above is for a single two speed fan. When high speed kicks on it turns off low speed. The Taurus fan needs only one speed hot at a time. The computer sends out ground to the relay. If you are running two fans, use one relay each and they will both run.

Pop N Wood

iTrader: (1)

You're diagram is doing the same thing as his.

You say you are powering the relays off the ECM? The ECM is grounding the one end of the relay (temp switches in your diagram), but the +12V should be a keyed 12 V source. That doesn't need to come from the ECM. Try hooking that straight to the battery.

Run the test with the jumper wires. That will tell you what you need to know. Like I said, you could have a bad connection. Or that first relay could be bad. A bad fan might draw excess current, but if your relay is chattering then something isn't holding the relay on. Check the connections to the relay coils first.

Tramminc

That's why I'm running a separate fuse and relay to each fan, just in case 1 of the fans fail, I'll still have the other one working to get me home.

74modified

I know it is the same, just using it for clarity.

Does a new relay start out this way or does it happen after a while? Swap the relays and see if you still have the problem - then it is a supply problem as Pop N Wood says. If not, the low speed relay can have its contacts burnt by back flow when low speed shuts off. The fan is still spinning and generates a voltage spike that can burn the contacts while they are opening. A diode can send the back flow to ground. You can use a standard 1N4002 diode from radio shack with the band side to the fan's low speed power + line and the other end (wide side of the triangle) to ground.

kwkrat2

iTrader: (2)

The relay's I am using have the diode in them. It does it with a new or used relay. the car hasn't needed the second stage of fan (except when the relay went bad). I definitly need to not have the second stage go through the first, incase of overheat like Tramminc said.
I haven't had time to do a voltage test yet, but should get to it this week. I can possibly pull 12v from the battery feed to power the the coil also and just have the computer ground. That would eliminate 2 wires from the ECM.