1986 Iroc 305 TPI, all stock but have converted to r134a and AC worked great for a year or so. I am currently having an issue with the cooling fan not coming on when AC is turned on. Fan will come on when engine reached temp, and when I put the vehicle in diagnostic mode. I have the GM service Manuel and followed all the trouble shooting steps, I have checked for power at the ECM (dark green wire) that comes from the AC compressor and I have power at the point.

I am assuming there is something in the ECM that then turns on the cooling fan. Has anyone come across this, is the only fix replacing the ECM.

 

I had this exact same problem.. replaced the ECM and it remained the same.


For mine,. it turned out the fan relay wires by the radiator were all corroded and eaten up from the grease they put in the connector at the factory....so the wires were touching and gounding etc..


I put some liquid electrical tape on it and it fixed it.


I WAS going to just replace the connector but seems mine has 5 wires coming out of the connector vs the replacements 4 wires.


Hopefully yours is this simple as well.

 

I checked that, did see the grease, at first thought the connector was melted but it was the grease, cleaned all that and still have the same problem.

 

It could be the pressure switch in the hard line then.

try pull the connector and see if the fan comes on. With it disconnected, fan should be on at all times with the enine running.


on the 86 it should be on the frame rail by the high side connector unless you changed the setup like I did