Newbie to this Board needs some help. If this is not proper Forum for this, please let me know and I’ll move it.

1227730 ECM, 350 SBC TPI with dual fans - The main fan (the driver's side) is controlled by the ECM. The second fan is not ECM controlled, but comes on anytime there is a request for A/C. All working as it should until recently.

Now, the main ECM controlled fan has started coming on with a cold engine any time A/C is requested (Max, Norm or Bi-level). Turn engine off and restart with A/C off and ECM fan is off just as it should be. There are no trouble codes. Any insight would be greatly appreciated?

The A/C condenser gives off the heat that is drawn from the passenger compartment. In order for the A/C to work properly the fan needs to be on to move air past it. Just like the engine radiator once it too gets up to temperature.

RBob.

RBob, thanks for the reply, but note that before something apparently changed, the EMC fan would NOT come on when A/C was requested, if the engine temp was below that set in the ECM. Only the A/C fan would come on. Now the ECM fan comes on if below ECM fan temp anytime A/C is requested and I'm trying ot understand why this is now happening.

I would double back on any changes that have been made. It may also have been something that was previously a bad connection.

In the f-body TPI '7730 wiring, the ECM has two inputs that can affect the main fan:

A/C request signal
Secondary fan active (fan request signal)

The A/C request signal tells the ECM that the compressor clutch is active.

The secondary fan active tells the ECM that this fan has activated. This is via the head temperature switch or the A/C high pressure line switch.

I've seen the interaction on the test bench. But never dove into the code to see why.

RBob.

RBob, how about this? Entire fan wiring circuits are solid all the way back to the relays. But, I did recently add a 12v LED to each fan’s circuit to let me know when a fan was on. LED hot wire was spliced into each fan’s hot lead from their relays just before it going into the fan connector. Checked everything with LED’s hooked up before installing in dash and everything worked just as it should. After installation, LED illumination is perfect and ground is solid.
LED’s are Radio Shack #276-0085, 1/4W, 660 ohm resistor for 12VDC operation (power dissipation = 180mW, forward voltage = 12V, forward current = 15mA).
I’m an electrical novice, but could the LED on the ECM fan somehow be affecting the ECM circuitry? I don’t see how because the AC fan is not ECM controlled. So, what could possibly cause the ECM fan to get current when AC is requested? If the hot LED wires of each LED were touching (and they are not), it would possibly cause the ECM fan to receive current when the AC fan was on. But then the opposite should also occur (ie – when the ECM fan kicks on at temperature, the AC fan should similarly receive current and light the LED, which it is not. Is that confusing or what?
The mystery is that the fan circuits, as you know, are totally independent, each being controlled by a separate relay. So how in any way could one receive current when the other is activated? Just makes no sense to me.

The point I was making in my previous post is that the ECM knows that the A/C compressor is active. And, it also knows that the secondary non-ECM controlled fan is active.

So why can't the ECM turn on the primary fan when it sees that either the A/C compressor is active or the secondary fan is on.

You haven't mentioned which BCC is being used. In the y-body both fans are ECM controlled.

Measure the voltage on ECM pin E8. If it goes low then the ECM is enabling the primary fan.

RBob.

BCC is a slighly modified AUJP, $8D mask. Will check E8 pin. Thanks.

I seem to remember that when I had my AC on, even when the engine was cold, that the primary and secondary fans would turn on. Turn AC off and both fans turn off, car warms up and only primary fan turns on.

Zepher, you and RBob are correct. I've traced and tested the ECM wiring and have confirmed that anytime A/C is requested on the 7730, that, regardless of engine temp, the ECM fan is turned on along with the A/C fan. I must have been in a fog when I did the testing before installation of the LEDs. Thanks!!!
Thanks for the replys. I think we can close this thread.