BBCSwap

91 Z28 350 TPI engine swap to sbc 400 carb. I don't know if the engine swap had anything to do with it or not. I did not cut any wires for the TPI, I folded the injector wires and related TPI wires that I'm not using against the wire harness. The A/C compressor runs and it blows cold air but the a/c related radiator fan does not come on. If I ground the green/w wire at the relay the fan comes on. If I understand the wiring diagram the ecm turns the fan on when the a/c is turned on. Any ideas what/where to check for the problem? Do I need to wire something different?

BBCSwap

I sure wish someone would comment. Any thoughts or ideas. I wish the fan would come on when the a/c is turned on like it used to otherwise I will hook up a switch but that's not really what I want to do.

blacksunshine'91

iTrader: (10)

Have you checked the fan swtich? It is located on the passenger side head, right above the starter. If it went bad (which is pretty common) that might be the cause of your issue.

Aaron R.

There is about a million posts about cooling problems such as this. Regulars are tired of repeating themselves. Try the search function.

1989karr

Did you leave he wires for the ac connected?

The nes I can think of are the one on the hard line and at the compressor.

BBCSwap

I removed the compressor when I did the swap so I unplugged the wires on the compressor at that time. They are plugged in now. The wires on the hard lines, low pressure switch & high pressure switch are connected. I will see if I can add more freon tomorrow. I charged the system enough to keep the compressor running and blowing cold air. I do not have a high pressure gauge so I can't check to see what the actual high pressure is.

1989karr

If the charge is too low the fan wont come on.. but itd have to be pretty low.

Another thing Id check is the wires at the relay. The wires like to corrode near the relay itself. I found mine was shorted and was grounding out and current wasnt making its way to the fan.

BBCSwap

I added some freon today. It made no difference. The drier is frosting up. I swapped the ecm. It made no difference. The wires at the relay look good. When I ground the green/w wire the fan comes on.

blacksunshine'91

iTrader: (10)

Do you understand how the fan switch works?

BBCSwap

Yes I understand how the coolant fan switch in the right head works. I talking about the other fan that is controlled by the a/c.

80schild

iTrader: (5)

I believe that one is controlled by both the pressure switch in the 3/8 aluminum line, and the coolant temp sensor. Either of those can command the ECU to turn the fan on. Four Seasons p/n # 36669 is what I replaced mine with. Could also be the connector itself.

BBCSwap

My switch tested open. I jumped the plug wires and fan did not come on.

1989karr

Try disconnect the fan switch on the hard line.


The fan should run continuously.

BBCSwap

I did. The fan did not come on.

vinny R

Does the fan turn on when the car heats up without the A/C on. If we are talking the 2 fan system the right fan, A/C fan, also gets turned on by the switch when the car comes up to 235 degrees. I believe both circuits go through the relay so even though the connections look good you may have a bad relay.

BBCSwap

It did last summer. I have not let it get that hot lately. When I back probe the green/w wire on the relay and ground it the fan comes on.

stew'86MCSS396

Soooo...it was fine when you had the TPI on there then it stopped working when you switched to a carb intake??? That tells me something that was installed on the TPI was removed with it (ignore the CS timer I couldn't find a 89-92 pic). True that the ECM is what turns the fan on but what tells the ECM to turn it on??? According to the schematic below, DK GRN-WHT wire should trigger the primary fan and the GRY triggers the a/c. What I'm not sure about is with all the stuff disconnected and the ECM probably lighting up SES lights all over the place...would it still control the fan(s) normally???

BBCSwap

The 350 TPI intake had one coolant sensor by the thermostat which is installed on the 400 intake by the thermostat.
The coolant temp. fan switch was in the right head on the 350 & it is in the right head on the 400.
And yes the SES light would be on but I removed the light bulb.
I don't think that is the schematic for the 91 350.
Before the swap the green/w wire relay was the one that would come on when the a/c was turned on.
The wires for the TPI that are disconnected are for the injectors, MAP, IAC, Throttle position sensor, distributor & the knock sensor. I thought those were a separate circuit on the ecm from the fans.