I have a 1997Pontiac Montana and the cooling fans don't work will work with a/c but not if van runs hot?

Question

coolant temp sensor was replaced.

Answer 1

You probably have a bad cooling fan control switch (sensor). It is supposed to make the fan come on when the engine gets too hot. The A/C over-rides the fan control switch so as to always turn on the cooling fan any time the A/C is turned on. Since you just replaced the coolant temperature sensor, make sure the connection is good between the sensor and the connecting wire and that the sensor you replaced wasn't just the sending unit for the temperature gauge. You know the fans work because they work with the A/C on. I'm not 100% sure on your car, but most cooling fan switches simply complete the ground when they reach the temperature to turn on the fan. You might use a test light to see if the wire coming to the sensor has electricity with the ignition on and the engine cool. The cooling fan may even come on as you test for electricity because by testing the circuit you may be completing the ground with the test light. If the wire has low voltage electricity, ground the wire to see if that turns on the fan (ignition switch on). There is a possibility the replaced sensor was defective or you replaced the wrong sensor. You have two coolant temperature sensors, one for the temperature gauge and one to turn on the cooling fans. They may be called the coolant temperature sensor and the cooling fan control sensor.

Answer 2

I own a shop, and I just fixed one with the same problem the other day. What it was, happened to be a bad relay. I think if you take a close look at your fans with the AC on, you will see that you only have one fan that works. If your cooling fan doesn't come on, then it doesn't come on when the AC is turned on either. I don't know if this is your case, but it could be. The temprature sensor sends ground to the cooling fan relay, the latch pulls in, and the relay sends ground to the fan. If the fan is bad, it won't run, or if the relay is bad, the fan gets no ground, and won't come on. Also; look where the relays plug into the fuse block, to see if there is any melted places, or bad connections. Some have more than one relay. It will have a main relay for both fans, and two single relays to operate the two seperate. One is called a cooling fan, and the other is called a condenser fan. If one fan comes on when the AC is turned on, then the main relay, and the one for that fan is working properly. You can jump out the relay to test it with a 9 volt battery and a meter. Find two terminals that have continuity, and this is where you hook the battery. You should hear the relay click, if not then its no good. Even if it clicks, then you must hook the meter across the terminals to make sure the latch is pulling in, and giving it continuity on the 1 ohms scale of the meter. The two that you get continuity on when the latch pulls in, is the two you can jump out with a wire in the fuse box to make the fan come on. This is based on a four pole relay. A five pole will have one side that continuity will fall off when the latch is activated, so you must use the two that powers up as the latch is pulled in. Most AC/Delco relays have a schematic (diagram) on it somewhere. The coil for the latch is indicated by a sign that looks similar to a lighting bolt. Don't worry if you hook the battery across the wrong terminals. This will not harm anything in the relay, but it will drain your 9 volt battery and spark. The coil for the latch always uses smaller terminals than the ones for the fan, and this is because there isn't many amps going across the (latch) magnet coil. The ones that activate the fan is the large terminals, and many times will get hot, corrode, and burn due to sparking of the two. Jumping these two out in the fuse panel is how one test the fan, and wiring to the fan. You do not have to have the ignition switch on in order to make these activate the fan, as the power is there already, and all you are doing is giving the fan a ground when you jump these out with a wire. If the fan is bad, or shorted internally, it won't come on when you jump these out.
If you purchase a "Haynes Repair Manual" for your vehicle, there is a wiring diagram in the back pages that will show you how its all wired. Remember, you are giving the fan ground to make it work, so you must also make sure the fan is getting a 12 volt supply, and you can check this with a test light.
Glad to help out, Good luck!!!

Answer 3

Hi Mark! Not sure what temp. your van is getting, but the fans aren't even supposed to come on until the engine temp. is above approx. 230 deg. I'd recommend checking your coolant level, if it's ok I'd have it scanned to see what the actual temp. is and if the PCM is commanding the fans on. I know the scan tool used by the dealer is capable of checking this and also can be used to manually command the fans to come on. If you have replaced the sensor, and the fans will come on with the A/C on I'd say you may have a PCM problem (assuming you are getting into the red on your guage). Most of the vehicles I've seen will get close to the red before the fans are commanded to turn on though.
Hope this helps!

Answer 4

By default if the A/C is on, the cooling fans are on. This is good because it tells you the fans themselves are working fine.

Since they are not coming on when the temperature goes above the trigger point, look to a bad sensor.

Answer 5

you need to replace the coolent temp sensor most vehicles have 2 sometimes 3, one for the pc,one for the fan, and one for the gage,, easy fix on that vehicle, go to parts store and they will tell you where its located,

Answer 6

Check for a bad fan relay also. Eautorepair.net has online access to factory service manuals and wiring diagrams for a small fee.