Radiator Fans not working when AC is on . . . . .

[Jerryl]

This is a HA car, with 87 ECM and dual fans.
The fans are controlled but the ECM via HD relay.
The fans activate and cycle fine when the temp gets to 160 F.

When the car is cold and running . . . . and the AC is turned on the fans do not activate.
AC works fine no issues and the relay tested good.

What got me thinking . . . . . On the IC’d car, the fans kick in when the AC is turned on.
I thought the ECM controlled the fans and would turn it on.
Please advise.

 

[GNVenom]

The ECM is independent of the AC for fan control. There is a switch in the high pressure AC line (on intercooled cars) that interfaces to the coolant fan relay. Basically an override control. To make the HA car work, you'd need the switch and you would have to wire it in so that the switch runs the relay when AC is running and pressure is present.

 

[Jerryl]

The ECM is independent of the AC for fan control. There is a switch in the high pressure AC line (on intercooled cars) that interfaces to the coolant fan relay. Basically an override control. To make the HA car work, you'd need the switch and you would have to wire it in so that the switch runs the relay when AC is running and pressure is present.

Thanks John!
I was thinking . . . . splice the relay ground and put in a manual switch to ground the relay.
Do you see any concerns with this?

 

[Flyin Brian]

I think you can just tap into the ac clutch wire and run it to activate the relay that controls the fans. You will need a diode in this run so that the fans coming on normally with temperature does not activate your ac clutch. I did this on my Tahoe and it works fine and is automatic.

 

[GNVenom]

I think you can just tap into the ac clutch wire and run it to activate the relay that controls the fans.

Problem with that is when the fans turn on, the AC will always run. Even when you don't need AC.

 

[rev. 3:11]

We're in Houston, we ALWAYS need the A/C!
D

 

[Flyin Brian]

Problem with that is when the fans turn on, the AC will always run. Even when you don't need AC.

A diode prevents that does it not? It works on my Tahoe.

 

[GNVenom]

If the AC clutch kicks in whenever the coolant fan relay closes, a diode won't have any effect in the operation. The factory AC clutch had a "snubbing" diode across the terminals to absorb the spike, but it didn't isolate the signal.

 

[RmvBfrFlght]

Thanks John!
I was thinking . . . . splice the relay ground and put in a manual switch to ground the relay.
Do you see any concerns with this?

That will work. The ECM activates the relay by grounding the coil terminal. Whatever you do don't put +12 volts directly to that wire, the ECM's quad driver won't like it.

Can't do it the way flyin brian mentioned. Even with the diode in series it would turn the fan on when the A/C clutch is off, not when it is on. The A/C clutch has one end always at ground, with +12 v supplied to enable it.

Can use the A/C clutch +12 feed to activate another relay for the fan. Having the two relays in parallel fan power wise.

RemoveBeforeFlight

 

[Jerryl]

That will work. ...........
RemoveBeforeFlight

Thanks for taking time to post.

 

[davelostmissing]

It would seem to me some kind of retriggerable delayed-off relay would be best.
If you are in AC mode continuing to pull heat out of the fins between cycles makes sense.

 

[RmvBfrFlght]

It would seem to me some kind of retriggerable delayed-off relay would be best.
If you are in AC mode continuing to pull heat out of the fins between cycles makes sense.

Yes, or use the feed from the dash switch. That way the fans stays on while the compressor cycles. Still needs an extra relay or such to use the +12 V as an active fan request.

RemoveBeforeFlight

 

[standupjskiguy]

You could get one of these instead of turning the fans on and off manually.
http://www.jcwhitney.com/engine-cooling-thermostat-switches/p2000903.jcwx?filterid=d239y1996j1
mount the bulb to the high side line coming out of the compressor or the AC condenser.

 

[BRAD_PADGETT]

This is a HA car, with 87 ECM and dual fans.
The fans are controlled but the ECM via HD relay.
The fans activate and cycle fine when the temp gets to 160 F.

When the car is cold and running . . . . and the AC is turned on the fans do not activate.
AC works fine no issues and the relay tested good.

What got me thinking . . . . . On the IC’d car, the fans kick in when the AC is turned on.
I thought the ECM controlled the fans and would turn it on.
Please advise.

Jerryl- Something is goofy with your setup. My dual fans start up once the A/C is turned on irregardless of engine temp.
I run the Caspers hot air single fan conversion kit followed by the dual relay Caspers 87 kit along with the dual fan start delay. TT Chip. Brad

 

[Jerryl]

Jerryl- Something is goofy with your setup. My dual fans start up once the A/C is turned on irregardless of engine temp.
I run the Caspers hot air single fan conversion kit followed by the dual relay Caspers 87 kit along with the dual fan start delay. TT Chip. Brad

Now . . . . THAT is interesting.
For some reason, I always thought that once the ECM saw the A/C Req. to be "on", it would ground the pin, regardless of engine temp.