tbroadfoot125

Greetings, I orginially posted in the Prom burning forum with a question about the Fan On/Off thresholds when the great members pointed out I had more issues then I thought. In a nut shell, I dropped a 87 TPI into my 83 Z28 and then updated to the 90-92 speed density. The donor engine had been stripped on numerous A/C parts and the compressor was seized up. I removed all the A/C, changed the firewall plate, A/C delete pulley etc.

I bought a after market harness for the car which was non A/C. When I purchased the MEMCAL from GM, it was supposed to be programmed without A/C. I followed a A/C delete article which had me ground D12 Fan Request Signal and jumper the two cooling fan relays in accordance with the diagram below.

But through the other forum, I found out that this was not right and needs fixed




So, looking through the schematics, I see that C9, (A/C Request Signal) comes from the ignition, through the A/C Fuse to the A/C On/Off switch, then through the pressure cycle switch, A/C High Pressure switch, to the compressor and with a junction into the ECM at C9.

My understanding of this is once the A/C switch is turned on, the ECM will see a voltage at C9. The ECM will send out a signal (voltage) at D12 (Fan Request Signal). So then when the Secondary Cooling Fan Switch closes and the A/C cooling fan switch remains closed, then the secondary cooling fan will come on.

So it looks like what I need to do is jumper C9 to the A/C fuse so that there is a constant A/C Request Signal. Then wire the secondary cooling fan back into the D12 Fan Request Signal circuit going through the Secondary Cooling Fan Temperature Switch. Does this sound right?

Tuned Performance

iTrader: (92)

Tuned Performance

iTrader: (92)

It does look like c9 to fused power would allow relay control d12.
I have good cooling results at on at 95c off at 85c.

tbroadfoot125

By the schematics, I agree with you about the fused power to the ECM. I also saw in the schematics that this is fuse is also for the heater blower motor, so I was thinking about putting an inline fuse between the fused power and the ECM to help protect from any high amps in case something goes wrong with the heater blower switch. Maybe a 2 amp fuse I was thinking.

Thanks for the great help and advise