what controls the cooling fan relay in detail please

 

I'm not sure which car you have...but I'm sure the hatch's and rexes are pretty much the same if you have an 89.

I would test your fan first to see if its bad. There is also a relay that is mounted on the inside of your right fender by the battery and a thermo switch (2 prong one) located on the back of the block, just above the oil filter.

Look through here and you can find some test procedures...88 FSM with 89-91 Supplements If you don't have a pdf reader try this one, its basically the same 91 Manual

 

I think the answer you are looking for is as follows (I think all this is correct, but I've made mistakes in the past);

1. There is a thermostat on the engine and when the engine water gets too hot, it turns on the fan.

2. There is also a connection to the ECU and it can turn on the fan. I don't have any idea what guidelines the ECU uses to do this.

3. There is a connection to the AC system and it can also turn on the primary fan at the same time as the AC fan is turned on.

Wes

 

The relay is "ground actuated".
There is a negative trigger wire coming off the relay. When this wire gets grounded, the relay closes the circuit and provides a ground for the fan motor.

The negative trigger wire runs to an ECT (Engine Coolant Temperature) sensor. The location for the ECT on a stock 88~91 motor is near the oil filter. It has 2 wires going to it with a rubber boot coving it. Other engines may have the sensor located on the thermostat housing.

There is another ECT located under the distributor which runs to the temperature indicator on your dash. This ECT doesn't do anything for the fan circuit.

Anyway, the ECT for the radiator fan is either open or closed just like a light switch is either ON or OFF. Normally the ECT is open. When the sensor reaches a certain temperature from the coolant in the engine it closes. When it closes then the circuit between the two wires that run to the ECT (the ones under the rubber boot) are shorted together. This provides the negative trigger to the fan relay.

ECT's do fail and it seems like they are one of the common parts to replace if your radiator fan doesn't work.


On a side note, you can add a manual switch to the circuit that allows you to turn the fan on whenever you want. Some people do this for drag racing so they can cool the engine while waiting in the lines to race on the track. All you do it run a wire to the ECT wire that goes to the relay. Hook the other end to your switch. Run a wire to ground for the other connection on the switch. Viola.

 

does this have any thing to do with the eacv

 

i thank that i had mine wired backwards

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by 89 pos &raquo;</TD></TR><TR><TD CLASS="quote">does this have any thing to do with the eacv</TD></TR></TABLE>

Absolutely none at all.

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by 89 pos &raquo;</TD></TR><TR><TD CLASS="quote">i thank that i had mine wired backwards</TD></TR></TABLE>

The ECT? You can't wire it backwards. It has two wires going to it and it doesn't mater which way you wire it.