I have a stock 305 and lately when my car is in traffic it has been getting really hot. Like up in the 240's hot. While im driving however it stays at a cool 160 or 170. So i decide to change the thermostat and the antifreeze. So i flush the system, put in a 180 degree thermostat (note that my old thermostat was in good condition when i pulled it out much to my suprise), and then refill the system. Well all goes well and im sitting it 160. So i drive to a bar to have a hamburger and as i pull in the my parking spot i leave the car on to finish a song im listening to. Suddenly my temperature goes from 160 to almost 260 in a matter of a minute. I take off my hood and look and see my fans are not going on, ****. Well after looking around i found a electric switch that is basically broken off my TPI intake. I have pictures coming in a second. One other thing i want to note. When i first turned my car on after refilling the antifreeze my compressor clutch was going on when i just had my heat on, i thought it only went on when a/c or the defroster was on. But seeing i was getting horriably high temperatures before and my thermostat seemed to be alright i think this fan problem has been occuring for a little while. Well here are the pictures. This is the area we are gonna zoom in on: Here is the switch thingy: This was the thing it was barley plugged into. The two little metal things sticking out of it are very corroded though and the switch doesnt snap into place like other switches like it do on the rest of the car. I feel like there was something else on this piece that is now missing. Looks like the engine coolant tempurature sensor to me but im not sure. And there you have it. Any help is much appreciated.

Thats your coolant temp sensor. It tells the ecm how to mix the fuel but has nothing to do with the fans. The fan switch is located at the rear pass side of head above starter, it kicks the fan on at 230 deg, and if you switch the ac control to max ac it should kick the fan on too.

Check the relay mounted by the radiator filler. It might be the same as one on the firewall you can swap it with.

I was looking at more than one post and thought you had a IROC. The location of the relay might be on the firewall. Drivers side. I think it's the one closest to the fender

Like he says

I had the same problem not too long ago with my '89 TBI. Replaced the sensor in the block hoping that was the problem, but wasn't. Wouldn't turn the fan on even with the AC kicked on. Turned out it was the fan switch relay, mine was on the driver's side firewall.


Good luck!

Alright sounds good thanks for your help. Ill check it out once this rain passes away, hopefully the really is the problem. Now i have dual fans.. am i right in saying that they each have a separate relay? I have searched many forums but everyone gives a different answer.

Im also thinking about also just sticking in a manual fan switch once i fix the problem so i can control when the fans go on and off.

Just to clarify this, your ECM controls the primary fan. The switching temp is around 220°. The ECM uses the coolant sensor to determine this temperature.

The secondary fan is controlled by the fan switch.

Both fans should run with the A/C on, be it MAX, Norm or, Defrost. This is granted the A/C system is working (ie: charged and the compressor works).

Even without the A/c system charged, at least the primary fan should run.

If neither fan runs, I would start with checking weather or not they work with direct power. From there I would check the under dash fuses and finally the relay.

Depending on what makes the fan(s) run depends on the next course of action.

Sorry to highjack but I have the single fan set up. It comes on around 220-230 like it should but when I turn on the a/c it doesn't kick the fan on. My system needs charged. I have read that it should kick on regardless of whether the a/c works or not and I have read on here that it wont work unless the a/c is working properly. I have an 89 2.8 with single fan. Any help on this would be great.

Well only my primary fan runs when my AC is on but i had a feeling my A/c system was not charged anyway.

I checked the fuses first thing and they are fine, I also changed the CTS(Coolant Temperature Sensor) and neither of the fans go on no matter how hot my car gets, only the primary goes on with the A/C.

Ill check to see if i can get my Secondary fan working today then check the relays and the fan switch. Wish me luck.

I have the service manual for 88 camaros. We all know the 89 is the same. Let me state that I am not a mechanic. I just try to do all I can on my own vehicles. Here is what the book says.

Circuit Operation..
V6 Vin S, V8 Vin F, and V8 Vin 8

The coolant fan is controlled by the ECM. In the V6 Vin S, the coolant fan is also controlled by the coolant fan switch. When the ECM grounds the 335 circuit, the coolant fan relay is energized and battery voltage is applied to the coolant fan. If the ECM fails(V6 Vin S), the coolant fan switch will ground the 335 circuit and energize the coolant fan relay. The ECM will ground the coolant fan relay when the coolant temperature sensor indicates the coolant temperature is greater than 106*C (222* F) or when the A/C head pressure is greater than 233 psi and the vehicle speed is less than 40 mph.

I'm going to ask at an A/C forum if refrigerant charge has anything to do with A/C head pressure. Maybe this info helps you.

Yes I think so. And if you can find out about the head pressure I would appreciate it. I tend to think it wont come on unless the a/c is working properly but I am not a mechanic either.

So i got under the car and found out the wire was not plugged into the fan switch. I plugged it back in and it still did not work. But i grounded the wire and the secondary fan came alive. Great! Now i have to fix the fan switch but the male end, along with the female end is broken. So is there anywhere i can buy a new male end?

Also i still can't get my primary fan to turn on unless the A/C is turned on. How does the Primary fan turn on other then the A/C turning it on.

Thanks for the help!

I have the same problem. A local mechanic says the temperature coolant sensor is gone. Not sure because i havent replaced it yet. BUTTTT My fans (two) would kick in when i unplug that switch that you are talking about. But this also regulates fuel so i would have a prettyh bad idle as a result. But when i unplugged this switch the fans came on right away and would stay on as long as the car was running.

Your local Chevy dealer should be able to get those parts for you.

Does anyone know what fuse would controll the fans on an 86 tpi 305?
My fan (single) will not come on even after replacing my regulator switch and my temp sensor. However when I try to plug a fuse into the acc fuse slot it blows instantly.

It looks like it's on the top row. Second from left. 20 amp between turn blu10 and the crk 3 fuse

Thanks Rock! That one looks OK. I am really stumped on this.

Did you read this in one of my previous posts?

Circuit Operation..
V6 Vin S, V8 Vin F, and V8 Vin 8

The coolant fan is controlled by the ECM. In the V6 Vin S, the coolant fan is also controlled by the coolant fan switch. When the ECM grounds the 335 circuit, the coolant fan relay is energized and battery voltage is applied to the coolant fan. If the ECM fails(V6 Vin S), the coolant fan switch will ground the 335 circuit and energize the coolant fan relay. The ECM will ground the coolant fan relay when the coolant temperature sensor indicates the coolant temperature is greater than 106*C (222* F) or when the A/C head pressure is greater than 233 psi and the vehicle speed is less than 40 mph.

Check your coolant fan relay. Should be located up on the radiator support bracket. Like below the filler neck. Somewhere on the drivers side rear of the engine is a coolant fan switch as well. You may have said you already replaced that. I don't have the greatest info on the 86 so, I'm giving you what I can. How hot is your car getting?

The a/c does not have to be charged/working for the fan to kick on when you turn the a/c switch to "On." However, you do have to have the a/c electrical components plugged in.

Here is the response from that A/C forum

The ECM for your Camaro drives or grounds the Electric Coolant Fan based on one of 2 signals: the Coolant Temp Sensor and/or the Fan Switch.

The Coolant Temp Sensor is a thermistor screwed into a coolant passageway, usually in the Intake, and it's resistance decreases as the Coolant warms up. It's getting a 5 volt reference from the ECM and as the resistance drops, more of that voltage reaches ground. The ECM then uses the voltage drop to calculate the Coolant Temp and when it hits 220 degrees, it drives the Fan Relay. This Sensor signal is also used for fuel delivery - the colder the temp, the longer the injectors are held open.

A/c operation has little to do with coolant temp (until it mucks up), so a normally closed, Pressure Sensitive Switch is screwed into the High Side. The ECM sends it battery voltage and when the switch is closed, the ECM senses 0 volts. When it's open, the ECM sees battery voltage and with that, it drives/grounds the fan relay. Mid to late '80's GM's usually open at around 230psi and reclose somewhere around 190 psi. In the overall scheme of things, GM has designed the system to maintain average head pressures (or the high side) at 200 psi and the fan (anytime it's less than 85 or so at the condenser), should be cycling on and off. Diagnosing the ECM is fairly simple: disconnect the harness at the Switch to simulate the open and if the ECM is working, the fan will come on.

Diagnosing the switch takes a Manifold Gage Set and since system pressures will vary based on ambient air temps, a Pressure/Temp chart for the gas you're using is helpful. At lower outside air temps - below 50 degrees, the high side may not reach the threshold for the switch to open (without some engine heat) and the fan may be off for some time or not come on until the Coolant Temp Sensor has signaled the threshold for fan operation.

Yes, a low charge can effect the High Side - but it also effects the Low where another Pressure Sensitive Switch cuts power to the Compressor Clutch. It's threshold is 25 psi and with a low charge, it may be/should be opening and closing rapidly causing the compressor to cycle on and off. With the compressor off, it's not going to make enough pressure to open the fan switch. Proper diagnosis requires a manifold gage set.

If your Camaro is overheating, you'll need to scan it so that you can see the Coolant Temp Sensor signal. Generally, a clean and fully charged a/c system will reduce non a/c Coolant Temps by 8 to 10 degrees. Once the compressor engages, pressure is built instantaneously, so the fan is coming on sooner and staying on longer with those models that use an electric cooling fan controlled by the ECM. It also needs a functioning thermostat to maintain proper coolant temps.