low speed fan won't work?

[subtlt]

Driving in traffic I noticed the temps up to 200 when the high speed fan came on. Got home and checked - no low speed fan operation (I run a JC93 which runs the fan all the time)

"Toasted relay" I thought - nope. Swapped relays and both work fine (grounded the green/yellow temp sender wire on the intake).

Turning on the AC did NOT turn on the high speed fan, so I'm thinking the signal from the ECM isn't getting to the relays.

Is there a fuse in this circuit? If so, which one?

I'm going out to re-seat the ECM connectors now, but if that doesn't work, which wire should I be isolating in the harness.

I loathe electrical stuff....

 

[OKTurbo]

If you haven't by-passed the low speed resistor at the fans, you might check there (and at the fan connector) to make sure everything is still secure. Those connections on the fans tend to get brittle and loose.

John

 

[subtlt]

It gets uglier

So I followed the wiring down to the big ceramic resistor and noticed that the wire was NOT EVEN ATTACHED to the resistor. It has split and the connector rusted off. So, if I understand this (and I don't think I do) I should be able to jump the resistor and the fan should work, right? It didn't.

This might be a stupid question, but do any of the 3 wires in that harness carry any power? I should be able to get a test light to glow if attached to a ground and probing each of the three ports, right? I'm not getting anything. Damn, I wish I understood this stuff...

 

[OKTurbo]

The three wires at the fan connector are.....
Blk/Pnk from the high speed fan relay. It will only have 12V when the HS fan relay is on OR when the fan delay relay is on.

Blk/Red from the low speed fan relay. It will only have 12V when the LS fan relay is on.

A lot of guys just take off the big ceramic resistor. With it off, the fan will run at high speed whenever the LS or the HS fan relays are on.

Make sure you're getting 12Volt to the relays. There is a Red wire going to each of the three fan relays. It should have power all the time. Check these and make sure you at least have 12 volts there. If not, the fusible link may have blown when your fan wiring came apart.

If you have 12 volts to the relays, you need to make sure the relays are sending the power to the fans when they are "on".

You can make the HS fan relay to turn on by grounding the coolant high temp switch on the intake manifold. Pinch the connector and pull it off......get a jumper and stick it in the connector and touch the jumper wire onto a ground like the intake manifold. This should pull in the contacts on the HS relay. If the fan doesn't run with this grounded, disconnect the fan connector and make sure you have 12 V on the Blk/Pnk wire at the fan connector (while you still have the temp switch grounded).

If you don't get power to the fan connector like this......you've got a bad wire or connection from the HS relay to the fan connector.

That should give you a couple of things to try......we'll get this figured out. Just don't let the "magic smoke" out of the wires.

John

 

[subtlt]

Getting there...

Thanks for the help!

The high speed circuit works - I grounded the wire off the intake temp switch and it worked. I then swapped relays, and it still worked, which means both relays are working.

So I've narrowed it down to the low speed circuit. If I ground either of the green wires I can hear the relay click. It also clicks if I command A/C, so I know that's working too. Due to the fuel pump priming, I can't hear the relay when turning the ignition to run, but I THINK that's working as well.

Tonight I'll see if when the AC is commanded, does the black/red wire get power? If so, I'll trace that wire to the connector at the fan, if it's OK there, then I know it's something at the fan. Does this sound like the right plan?

I don't really want to jumper the resistor, as with my JC93 chip the fan runs all the time. I'd think running it on high continuously wouldn't be too good on a daily driver. Is this resistor GM specific or would an electronics shop have an equivalent?

Thanks again,

 

[OKTurbo]

If the low speed relay in on, the Blk/Red wire should have 12 volts at the relay and at the fan connector. If not, you've got a bad connector or wire somewhere from the relay to the fan.

If the fan runs on high speed, there is nothing wrong with the fan. Running with out the resistor is fine.....I did it for years when my car was a daily driver. Even if the fan runs all the time...the Thermostat won't let it get below 160 degF.

I'm not sure where you would find another resistor. Might try radio shack.....or the scrap yard....I'm sure someone on this board would sell you one pretty cheap. My old one is missing in action since I've gone to the Ramcharger dual fan set-up.

John