So I removed the AC in my 1991 dual fan car. My 2nd fan never comes on now. I'm assuming this may have something to do with the wiring to the AC being terminated (not connected). I believe the passenger side fan is controlled by the ECU in my car. Is there something in the AC circuit that requires a connection for the fan to come on when needed? The fan does come on when a ground out the wire to the sensor. If the AC being disconnected/removed is the root of my 2nd fan issue, does anyone have any suggestions on how to make it come on without having to wire up a switch?

 

The aux fan operates when head pressure from the A/C reaches a certain parameter, when I get home a can snap a picture of the diagnosis and the diagram that has that circuit, and how it interfaces with the relay combo for the primary/aux fan.

There is a 2 wire connector that is plugged into the A/C hardline tucked under, just aft of your coolant reservoir.

 

This may help ya out

 

Awesome. Thanks. Does it only come on when it gets that high head pressure signal from the A/C line switch? I thought it also kicked on when the temp got to some specified limit. 220f I think? I ran my car above 220 (checked with infarred thermometer) and it never kicked on. So I replaced that switch on the block thinking it was not sending the circuit to ground. That did nothing. Which is why I started to think it needs the a/c in there somewhere. But it looks like if I jump out the wires to the a/c pressure sensor it will only come on when I have the dash selector set to ac right?

 

It kicks on at 238ish. Also, while I was charging my AC last week, in the garage, 95*, I did notice as the pressure went up on the high side to like 250psi and climbing, it DID kick the fan on and brought the pressures down. It repeated this process throughout the charging process as it cycled.
Let you car sit and idle. If they are working right, the second fan will eventually come on.

 

Thanks Bob. I guess I got impatient. I wish it would kick on sooner. Like somewhere in the 200-210 range. My car does not overheat, but i climbs so fast when sitting at a red light. The primary fan seems to keep things in check but it seems silly to only draw air across one side of the radiator. Is there a compatible fan switch that works to make the aux fan kick on at a lower temp? I have my primary set to turn on at 180 in the prom. I figured 200-ish for the aux fan would probably not be a bad idea.