# Radiator Fan Operation



## caribconsult (Jul 9, 2017)

CAR: 2006 Sentra 1.8S.

Issue: large cooling fan, US passenger's side, also listed as "left" side...(left side of what?) It's on the USA passenger side and will be referred to as PSF. The other fan, the one listed as "right side" is on the drivers side and seems to work in conjunction with the A/C compressor, and will be referred to as DSF

The DSF fan working in conjunction with the a/c seems to work property. It cycles on and off with the compressor clutch. THE CAR DOES NOT OVERHEAT. Turning off the a/c means NO fans are working but the temp needle doesn't move. It actually drops just a teeny bit when you run around on the road instead of idling standing still. REPEAT: it does not overheat whether any fans are working or not.

THE PSF fan never seems to go on. It has a new motor. It has 4 connections and one of them has 12vDC on it when the A/C fan. I have never seen this fan go on. As stated before, the car does not overheat. The temp gauge consistently sits at just below the halfway mark and stays there, A/C on or off, sitting running idle in 90+ degree weather, or running on the road, up and down mountain roads, nothing seems to move it except the engine getting to operating temp.

*So what is the story with the big PSF fan? When is it supposed to go on? Under elevated temps? At What degrees? Is there a relay possibly defective? I looked in the fuse box under the hood and there's a label for "FAN2" but no relay in that socket, not at least according to the drawing on the cover. If there is a relay, is there a part# or description and please show the exact location? It could be something really simple, like the relay.*

I would greatly appreciate some technical help here about how and when the larger fan cycles on and off


----------



## caribconsult (Jul 9, 2017)

I have a block diagram of the cooling fan cirsuit an it shows just two relays to control the motors. Each relay is double pole, so the equivilant of two switches. I'm starting to suspect one or both relays and I think I'll need two new ones. As I understand it, the right side fan has two speeds. it's on and off low according to temp, a/c on or off, but when the A/C is on it switches to high speed. Does anyone know if that's how they works? New fan relays next. will post results.


----------



## John Clark (Jul 26, 2015)

So, to carry info over from the other thread in the wrong forum....

Here's how the fans are supposed to work. The fans are two speed fans. 

The fans should come on low, regardless of AC on/off, when the coolant temp reaches 208F at any speed, or if the AC is on and below 212F coolant temp. If the vehicle speed is above 50mph then the fan won't come on low until 203F coolant temp.

High speed will come on regardless of AC on/off at 212F coolant temmp. High speed is also triggered when the refrigerant pressure reaches 229PSI, which essentially means any time the AC is on. 

There are two fans, one with four wires and one with two. There are also two relays, a high and a low. What gets a little complicated is that both the relays have two contacts in them so they each control two circuits. Additionally, the PCM controls the speed of the fan with a low output and a high output. 

From the diagram, it appears that the two wire fan only runs on one speed. The four-wire fan runs on either a high or low speed depending on what the PCM tells it. At idle with the AC on (if the AC is working and has pressure in the system) both fans should be running on high. 

Here's where I would start. Check the fuses. There are two 40A fuses (I & H) in the underhood fuse and fusible link box. There is also a 10A fuse (#20) in the Fuse Block junction box (I think that's probably inside the car but I don't know for sure.)

If the fuses are good, then start the engine, turn on the AC and tell me if there is power getting to the #2 pin (green/yellow) wire going to the 4 pin connector on the inoperative fan.


----------



## John Clark (Jul 26, 2015)

Your AC needs to be working normally in order to test this way. If your system is undercharged or compressor doesn't work then the fans won't turn on when you turn on the AC.


----------



## caribconsult (Jul 9, 2017)

The A/C seems to be working quite normally, the clutch cycles on and off, and the left side fan (driver side) cycles on and off with it. I didn't see any signs of a burnt fuse it that group of 40a fuses, so the relays, I think, will be the next point of suspicion. Are there also fusible links in these circuits besides the 40a. fusing? Can you just pull them out and test with an ohmmeter?

Thanks again to those who replied. All this advice is very helpful.


----------



## caribconsult (Jul 9, 2017)

I do believe I checked that wire you mentioned and there was +12v on it when the a/c fan came on. I didn't check the other 3 terminals but is starting to appear that if either relay is acting funky, the system won't work in various ways- the a/c fan might or might not come on, and the bigger right side fan might not, which is my problem here. Relay checking next. The motor I took out of the fan housing turned out to be ok...it ran when 12v was applied, and had two speeds.


----------



## John Clark (Jul 26, 2015)

What are you using to test? Do you have a test light? That's better than a multi-meter for testing this circuit but a multi-meter will work but can sometimes lie to you as it can't carry any current.

If the engine is running, AC is on, and the two-wire fan is running, then you should have also have 12 volts on the green/yellow wire, as well as the yellow wire going to the bigger four-wire fan. If you have 12 volts at the green/yellow wire then that means the cooling fan relay 2 is closing normally. If you have 12 volts at the yellow wire then that means the cooling fan relay 1 is closing normally. If those are both powered, as they should be, then that just leaves a ground problem. Using your test light clipped to a good ground somewhere (or volt meter if that's all you have) and the connector still plugged in, engine and AC still on, check for 12 volts on the other two wires (ground wires.) If the ground is open you'll have 12 volts on the ground pins. If the grounds are good you'll have near zero volts (or test light not lit) on the ground pins. One of the wires gets it's ground from the cooling fan relay 2 and the other goes directly to ground. 

Post back your voltage findings on those wires.


----------



## caribconsult (Jul 9, 2017)

For testing have a car tester with a bulb in it and a needle pointed probe that will pentetrate insulation. I also have VOM multimeter. There is 12v on the wire specified. I checked the connector plug on the new motor I bought (right side two speed) and one of the contacts in the motor side of the connector was pushed into the plastic body of the receptacle on the motor. Obviously not making contact with the harness and it's the 12v line, the one at the upper right corner as you look down onto the connector on the motor. I managed to extract it a bit with some needle-nose pliers, re-inserted the connector carefully and now the right side fan will go on with the left side fan that seems to work with the A/C circuit. If I turn off the AC, both fans shut off. The indicated coolant temp (OBD on laptop) is hovering around 176-182 deg F. no matter what is running. I swapped fan relays and there was no change in operation so I believe the relays are good. If the a/c is on, both fans go on with the a/c compressor clutch engagement, and go off when it disengages. At least the car is driveable now, because you'd almost always want the a/c in our tropical weather.

So now what would trigger the right side fan to go on if the AC is off? Does the engine have to reach a certain temp like 212 F as you mentioned above and then it kicks on, or if it's already on because the A/C is on, does it go into high speed? Is this how that fan functions? According to the OBD readout, coolant temp holds pretty stead around 180. So how would I know this fan will kick on unless I dangerously overheat the engine? I'm not so sure it's important any longer since the fans both work with the AC on, and that's about all the time.

Thanks again for your terrific help.


----------



## John Clark (Jul 26, 2015)

In post #3 above I described for you what triggers the fans. With the AC off you need 208F to get low speed fan operation. If you're coolant temp is showing 176-182 then the fans will not run. 

It sounds like your problem is solved. If you see 208F or higher and the fans don't come on then I'd say you have a problem. You should notice your AC working much better now that both fans are working with the AC on.


----------



## caribconsult (Jul 9, 2017)

That's pretty much how I feel. I can't see it overheating with both fans running, and I'm sure there got to be a little improvement with the additional air flow over the condenser, although the a/c on this car always was excellent. 

Thank you again. Your advice and explanation of the logic of the fan system was immensely helpful and nice and clear. Muchísima gracias.


----------



## John Clark (Jul 26, 2015)

The reason both fans need to run when the AC is running is to remove heat from the condenser. If you aren't flowing air over the condenser, or over part of the condenser, then the heat in the condenser will be retained and pressures will rise in the high side of the system and AC efficiency will be reduced. 

When your AC is off your temp is staying under the 208F so you're not going to see any fans run and you're not overheating...as long as your coolant temp sensor is reading correctly.


----------

