91 Trans Am with the "Heavy Duty Cooling" package (2 fans), passenger side fan isn't operating. I have replaced both fan motors and relay on driver's side firewall. Driver's side fan operates correctly when the A/C is on and car is <5 mph (high pressure switch) and at 220 (normal operating temp).

I've seen this posted here a couple times, and someone inevitably tells that person to install a switch. I can't do that, as I would rather not have to train someone to operate my car. I would rather it worked like it is supposed to.

Chilton's references a 2nd relay for the PS fan, but I'll be damned if I can find it. I'm turning to you all here to lend a helping hand.

 

Does the passenger side fan come on with the AC? It should. Have you checked the fan switch? It is located in the passenger side head, between plugs 6 and 8. A quick way to check is to disconnect the wire, and connect this wire to ground. Your passenger fan should come on.

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1989 IROC-Z 5.7L
NOS 150HP kit
ProBuilt 700R4, PI Vigilante 2800 stall lockup
Baer Brakes 12" Sport System

 

Also, if your '91 GTA is anything like my '91 Z, I believe both relays are on the firewall, drivers side.

KAM

 

If you want to test the fan from the relay socket, just remove the relay from its socket (located next to the driver's side fan relay [there are a total of three; fuel pump, fan 1 and fan 2] on my '91 Z28) and then connect together the two largest wires on the relay socket. The engine can be off.

One of the thick wires goes to the battery (via a fusible link) and the other thick wire goes to the positive fan motor power. The fan ground is permanently wired.

If the fan does not work, then your fusible link may be bad, the fan motor may be bad, you may have a bad ground to the fan motor, or the wiring between the relay socket and fan/batter may be bad.

If the fan works when shorting these two wires together, then either the relay pin(s) are not making good contact with the relay socket or any number of other possibilities.

The above simple test should get you started troubleshooting.

 

I had switched the relays (they are the same part number) before I posted. I switched the temp switch (between #4 and #6 plugs, but was unable to ground this to test if the switch was initially bad. Before switching it I jumped the orange power lead with the black/purple wire and the fan came on. It will have to go to the dealer**** and get them to look at it.

Thanks to all those that helped I really appreciate it!

 

The secondary fan is controlled by both the coolant temperature switch in the passenger side cylinder head, and the A/C high pressure switch, located in the A/C liquid line (on the passenger side). The A/C liquid line switch will close only when the liquid line pressure exceeds 232 psig, so the secondary fan will usually operate only when it's very hot outside, and the A/C is on. You may test the pressure switch by disconnecting the primary fan & running the A/C. Without air moving across the condenser, the compressor head pressure will increase very fast & the secondary fan should turn on.

Tim

 

Has anyone tried wiring the fans to come on together and bypassing everything else. Basically what I mean is having the driver's side fan come on regularly, but wiring the passenger's to come on with it. Would there be any disadvantages to this.

 

Unnecessary electrical system load, especially with under drive pullies installed, unnecessary fan motor wear, and in the winter, when the defroster is run, much more air flow across the condenser and radiator than would be necessary, as both the A/C compressor and cooling fan run in defrost mode.

Tim

 

Friday morning on the way to work, I blew the heater hose I use to bypass the throttle body (definitely not needed here in Phoenix). In order to clear the steam I turned the key on, and what do you know, on comes the fan. Oh well. All is well now and I wanted to thank all for their support. Oh, and the temp sensor is physically next to the #6 spark plug, not down low on the '91 lb9. The lower one turned out to be the knock sensor. That also explained why grounding the wire didn't make the fan come on. ;-)