Yes I have a 1992 z28 and only one cooling fan comes on, does this mean i have a defective cooling fan or relay or is it not getting hot enough for both fans to come on? I just put a new motor in it, and its still not coming on.


Is there a way to test to make sure both are operating properly?


Thanks Matt

 

You need another person - trace the wiring to the relay, then hold the relay while someone turns the A/C switch to ON, then turns key to ON - fan should run with A/C on - if you feel relay 'click' but fan doesn't run, then test fan by applying 12v directly to it. If relay doesn't 'click', then replace relay.

The secondary fan comes on when either 1) fan switch in pass side head reads 238 degrees, or 2) when A/C is on.

You can test the wiring from fan switch to relay by grounding the connector to the fan switch - if the relay and fan are good, grounding the fan switch wire will make the fan run (with key on of course).

If fan relay works, fan works, and fan switch wire is good, but fan never comes on above 240, then might have a bad fan switch - replace it.

 

Matt, I was just about to ask this ... Thanks for the question! It sounds like mine is similar to yours - Or maybe I'm just confusing which is primary/secondary and which side driver/passenger those are found.

On mine, if I turn the A/C on the DRIVER fan comes on instantly. When I shut the A/C off, the fan runs an additional 65 seconds. That same fan (DRIVER side) is the one that comes on when the temp sensor reads 238 degrees.

I've never seen the PASSENGER side fan come on. I thought (incorrectly perhaps) that the A/C fan and the temp sensor fan were not the same fan unit. When should the passenger one come on? And no, my car never overheats.

Mike

 

Maybe the driver side fan is the secondary then - I may be confused (my wife says I was born that way).

Anyway, it's the secondary that comes on with the A/C and fan switch at 238, the primary is controlled by the ECM.

 

If the car is past '87, both fans should run with the A/C on, unless the A/C doesn't work (not charged).

To find the secondary, just ground the fan switch wire (pass. head) to the block with the key on. Whichever fan start spinning is your secondary.

The ECM should switch the fan that isn't the secondary at 220*F. The secondary just kind of hangs out unless the A/C is turned on or the car boils past the 238* mark.

'87 dual fans, the primary did everything and the secondary was just tied to the fan switch. It did nothing but take up space for the most part.

With the key on a jumping the a-b terminals on the ALDL (running codes), the primary should start up. If it's not, start with swapping relays, they are all the same under the hood. If it runs then, you have a dead relay. If it doesn't work yet, start testing wires for voltage.
If all checks out and still no fan, it's may be an ECM/wiring to ECM issue.

 

.

 

Old thread, but I have an 1987 5.7 IROC so how can I make the secondary fan (passenger side) play a more active roll in cooling? Just change out the switch in the head with a lower temp switch?

 

Yeah, exactly. Just put in a lower temperature switch.

 

Wells sw555 or summing has a ton of single wire switches with different on/offs to choose from.
iirc it’s 3/8 npt
https://www.summitracing.com/parts/mar-mfa109


https://www.summitracing.com/parts/rfw-ar34

 

Or you can wire the relay ground to the other fan's ground. that way it'll come on at the same time

 

Now I realy love that idea having both fans come on at the same time. Can you give me a bit of information on the relay ground. Both fan on will help with the a/c as well I bet as the condinser will have more colling air going through it.

 

Both relays have constant power, and when the relays are grounded, they close the contacts and send power to the fans.

Assuming they are working properly though, then the only difference in operation is when / how the relays are grounded. Usually the passenger side is the primary, and driver is secondary... Its possible yours are just connected opposite at the motors though.

But basically if you splice the relay ground wire from the secondary fan into the primary fan relay ground, they will both activate when the primary fan comes on as they will both ground at the same time.

The DOWN-side is that if the primary fans ground area fails for whatever reason, you have no secondary backup... but honestly, that's a kind of a rare scenario / even if it happens youd probably notice if the car starts to overheat / ac stops working etc.. most dual fan cars are wired this way anyway. these days and even my 90 camry was wired this way.... I think GM was the only one who wired fans to come on separately back in the day.

Ive done this done to my fans and honestly, the dual fans really helps improve cooling and ac performance noticeably.

 

You can turn on the a/c and the 2nd fan should come on. that's how I ride in the summer anyway!

 

I think that was for 90 plus. both fans would come on for the ac


On older models. I think 85 or whenever dual fans were introduced, to 89 or maybe it was till 88, only the passenger side fan came on for a certain temp and for the ac. The second fan was purely operated by the fan switch in the head.

 

I live in North Fl would a temp switch of on at 176 and off at 161 be too cool for winter driving and not let the computer system go to open loop?

 

IMO yes.


Plus youd have yo crawl under there to change the fan switch...


if you want to have different temps for seasons... Id personally get that auto meter adapter for the radiator hose and extend the fan switch wire... that way you can at least change the switch very easily

 

Thank you for the insight on the secondary fan relay. Would someone be able tell me where the relays are located? Also what color wire I'm looking for to ground the second fan to the relay on a 1987 5.7 TPI duel fan set up? I have the 1987 GM factory service manual but I can't read wiring schematics at all..

 

The relays are on the firewall left of the master cylinder.

Instead of splicing one relay ground wire to the other relay ground wire, what if you ran a jumper between the two? So when one relay gets triggered it triggers the other so both fans come on. Or would that mess with the ecm? If so, what if you would run a jumper between the power wires at the fans. Would that make both come on when one relay is triggered and not hurt anything?

 

If i remember correctly, on a -87 TPI, one (or both) fan relay is below the radiator cap near the air filter, thats on a Trans Am, on a Camaro, its the same location or on the firewall below the driver side windshield wiper. The other fan relay is on the firewall as well, next to the MAF relay and MAF burn off relay and fuel pump relay, if im not mistaken, i could be.

On -87 and older, they are square relays, on -88 and newer, oval relays.

I don't know about the color of the wires, but i read from somewhere once that rigging the fans to come on at the same time, may blow the fuse eventually cuz they weren't originally designed to come on at the same time, but i've doubt it would blow a fuse. As others stated, i would just replace the sensor on the passenger side head between the spark plugs, with a lower temp sensor such as standard motors "ts136" sensor, that way the other fan comes on around 210F or something, and if ur stat is OEM temp 195F, it should work just fine, otherwise the fan is on and off all the time if ur stat is 195F and the temp switch is lower temp setting than that.

As others stated, the ECM controls the other fan, but that i believe can be changed with a custom chip for the ECM, if u want the other fan to come on earlier, but its easier to mess around with the sensor for the other fan, i wouldn't mess with the ECM controlled fan, specially if ur car is stock.

The original temp switch on and off setting is quite high, meaning it barely ever triggers the other fan, i would just replace it with a lower temp switch and call it for a day.
Standard Motors temp switch ts136 ought to work, if u want to read more about temp switches, check out this, they are for Fieros, but ought to work in our cars too, but pls double check about the fitment before if u buy/change the switch, that if it fits. https://rodneydickman.com/product_in...products_id=95

 

I was originally going to do this... but it turns out the relays have constant power to them for both the power going to the fan, and the power to the "activation" of the relay. The relays complete the circuit and controlled by whatever grounds them.. ECM/ fan switch, ac etc...

 

Hey I wanted to thank everyone for the help. I installed a lower temp fan switch (on at 195 off at 185) and the a/c is cooler. I can now stay at normal and got to max on the a/c panel. Also the temp gauge stays aorund the hash mark before the 220 mark and that's in stop and go driving with an OAT at 95.

 

Would you share the brand and part number please. And what thermostat do you have? Does the fan come on when they claim it does? Does it cycle on and off or just come on and stay on?

 

Hey I used this switch https://rodneydickman.com/product_in...products_id=95 and it fit perfectly I did purchase a new connector as well. I have a 180 thermo. The fan does not run all the time even when I have the a/c on. I'm not sure if it come on at 195 as I have not hooked a Tech 1 up to the port to see the actual temps.

 

I found this thread when searching for the rating of the TS136 switch and wanted to revisit it to include some info.

I was messing with my cooling system and ordered a new fan temp switch that was supposed to turn on about the same temp as the Primary fan; about 220 degrees ( Thompson 3736). After installing the switch the fan still didn't operate; I even disconnected the primary and let it run till I started to boil over - still no secondary fan. So: I tested the fans ( good ), tested the relays ( good ) tested the wiring ( good ),... so I started trying to figure out a way to manually control the switch. Since this car is an 88 TPI I couldn't just use the AC on signal because the HVAC controlled sends out switched power when the MAX AC button is pushed and not switched ground like the cooling fan relay wants. Rather than rewiring another relay in place to send switched ground when the AC MAX button was pushed I tried to install a JUMPER wire from the Primary relay to the Secondary relay.

Car has a 180 Stat and gauges reads about 190 when the thermostat opened ( tried 3 different switches,.. thinking the gauge is a little off. ) Once the car reached about 220 (230 on gauge) the Primary fan and the Secondary fan activated. ( YAY !!! ) BUT: the fans would not shut off. ( Boo !! ) The fans continued to run showing 190 on the gauge - meaning the fans were fighting the Stat. While still running: as soon as the jumper wire was removed from the secondary fan relay the fan quit turning,... and after about 10-15 seconds the primary quit turning. The same thing was true no matter where I attempted to jump into the secondary relay with ground. ( GREY wire @ AC pressure line switch or the GREEN/White temp switch wire ). While I'm guessing I could have continued down-this-road by installing a cooler Stat I'm GUESSING that they both would have stayed running no matter what using the "jump-the-relay" method. I do not know why, but the ECM would not kill the switched ground signal to the fan relays when the ECM switched ground was jumped to the secondary relay.

It was obvious that I had a shelf-dead Fan Switch and just didn't want to buy another switch so I tried a hack. ( FAIL !! ) In the end I bought / installed another new switch; Thompson 3737 ( adverized fan on @ 212 degrees ). Now the secondary fan activates about 220 ( on gauge ) and the primary fan activates less than a minute later. Both fans shut off properly with the secondary shutting off first and the primary shutting off less than a minute later. The primary fan will only turn on when the car is RUNNING,... but the Secondary fan will operate when the key is turned to RUN if the temp is hot enough. Seems perfect since both kinda' work together - but are still wired independent of each other so if 1 fails - there is still a functional fan.

Pretty long-winded way to say that just installing a switched ground 'jumper wire' from relay to relay isn't a good idea unless you're OK with your fans running at all times when the car is running.