Mulcreevy

complex for me anyway! I noticed a few times in traffic that temperature was too high (260). It also got hot one time on the freeway. Over the last year I have replaced thermostat, water pump, radiator cap, flushed system a few times; temperature sensor, and relays were done recently.

The fan used to come on when I turned the a/c on. It does not do that now. Before it quit coming on the relays were making noise that was so loud I could hear it when I was driving. I replaced both relays and they still made noise. They stopped making noise but the fan is not running now either. This sounds like some kind of electrical issue but I cannot find in my searches how to fix it.

travis401

iTrader: (1)

the relay noice youre hearing is the relay clicking which it does when it turns on. not hearing that click and them not running points to the relays not working anymore. apply 12v to the relay trigger wire and see if you can hear the relay click.

Mulcreevy

hmmmm what you are saying makes sense except that for most of the years I have owned the car I could not hear the relays. They are loud enough to be heard over road noise and the clicking is really fast. I would not think they should be cycling so much, but I am not that familiar with relays either.

amlv20

loose connection or wire chafing on the primary control circuit either the power or ground wires could cause the relays to cycle on off, if its a module controlled primary circuit the transistor can be going bad.

Mulcreevy

Thanks, I appreciate your input. Can you tell me what the primary control circuit is? The electrical side of things is a little over my head but I would like to learn.

amlv20

primary is the control circuit of the relay, the power input to the relay coil and ground that activate the coil. the ground to the relay is usually controlled by the ecm.

torque_is_good

put power directly to a fan to make sure they work; you need to eliminate that

overheating on the highway..........do you have the air dam?

305sbc

iTrader: (3)

Often there is a backup fan control switch (one wire) installed in the passenger side cylinder head. I would check that and make sure the wire hasn't melted or shorted to ground on the exhaust.

travis401

iTrader: (1)

thats not a backup, its the fan switch and its only on the dual fan systems, or the single fan tbi systems.

on the dual fan systems the primary fan is controlled by the ecm and the secondary is controlled by that fan switch and the AC has an override feature.

on the single fan TBI system the fan is controlled entirely by that fan switch with the same AC override. on the other single fan systems the fan is controlled completely by the ECM.

Mulcreevy

That sounds like a good test. How exactly do you do that?

one92rs

iTrader: (5)

on the third gens single fan switch controlled with a/c on.
on third gens with duel fans 1 ecm and the other switch with a/c on.

here is the schematic for your fan.
http://austinthirdgen.org/mkportal/m...ine_wiring.gif

giovanhalen

If you are rolling down the road your fans should not be coming on in the first place. Enough air passes through the radiator without the fans coming on. You might want to get a new radiator.

deadbird

'87 older, a/c only called single fan via ecm. '88+, A/C will run both fans. 1 - ecm fan request (via a/c pressure switch input). 2 - a/c pressure switch is tied to fan switch circuit, too. Just adding (somewhat useless) info to what was stated.