Cooling fans won't run

[dantatara]

2002, 3.4. Here is an overview. They won't turn on either when the engine in warm or when the AC is on. In the fuse block assembly under the hood I pulled the low and high speed relays, jumpered the contacts and the passenger side fan works in both modes. Now the other fan relay has a normally closed and open set of contacts. Jumpered across them and the other fan doesn't turn. (Not sure at this time if that means anything). I took the battery off for 15 minutes, thinking may the computer needs reset, no change. Where is(are) the temp sensor(s)? Is the only way for me to get my hands on a schematic to buy a Repair Manual? Do the repair manuals have all the electrical drawings? I will appreciate your input or solutions or questions.

[cdru]

Their is only 1 temp sensor. It is located on the drivers side of the lower intake manifold, just before the thermostat and elbow leading to the upper radiator hose. If you look just below teh throttlebody, you should see it there. Your fans kick on around 230 or 235 degrees and shutoff around 215 degrees. Normal operating tempatures while driving should be around 195 so the fans won't normally be on (unless the AC is turned on).

A Haynes manual is always a good investment, especailly at $15 or so. The wiring diagrams in the back leave a little bit to be desired but should be sufficient for what you want. A shop manual is preferred if you want something specific to your year. You can find them on eBay occasionally at a reasonable price. I got mine new for $35. Current prices look like around $80 or so.

[DRW1000]

I am not of how the Venture works but assuming it is the same (or similar)as my Windstar;

The PCM controls the fan. It takes the reading from the temp sensor, speed sensor and A/C and decides where and what speed the fans should come on at.

I mention this because the fact that the fans don't operate with either the A/C or Temp Sensor may indicate that the signal from the PCM is the problem. It also may be that the ground or Vcc of the controlled part of ther relay may be at fault or have an open.

I will look at my Haynes for my Venture and see if the wiring diagrams might help. I would certainly invest in one as it pays for itself for pretty much any repair. Sometimes I just use it as a torque spec reference.

[GregA]

Originally Posted by dantatara

2002, 3.4. ... In the fuse block assembly under the hood I pulled the low and high speed relays, jumpered the contacts and the passenger side fan works in both modes. Now the other fan relay has a normally closed and open set of contacts. Jumpered across them and the other fan doesn't turn. (Not sure at this time if that means anything). ... Is the only way for me to get my hands on a schematic to buy a Repair Manual? Do the repair manuals have all the electrical drawings? I will appreciate your input or solutions or questions.

I have a page that tells about the cooling system fans. This is for the 2001 Venture, but it is probably the same (or pretty close). It includes a schematic. You will note that there are 3 relays that control the fans.

Engine Cooling Fans

Haynes manual has the same schematic (basically), just a bit harder to understand. If you need any help with interpretation, just let me know.

Take Care,

[dantatara]

Thanks for the sensor, manual, and PCM info.
Greg, thanks for the system cooling fan info and schematic. I read through it and one item stands out and that is this; a Fans off item, "The A/C refrigerant pressure is less than 190 psi (A/C off)."
Well the AC barely cools the air. In doing a process of elimination earlier, I found the fans not to turn on. I was thinking it was why the AC wasn't cooling, however when going at highway speeds I thought it would cool some, and it didn't. Anyway, if the AC preasure is below 190PSI my fans will never come on! I think this is what I'm reading. Therefore telling me I have a AC system leak/failure. I will try in locate the AC pressure switch. If you know, that would be great. If I can bypass it and have the fans work.
Thanks again

[cdru]

Originally Posted by dantatara

Thanks for the sensor, manual, and PCM info.
Greg, thanks for the system cooling fan info and schematic. I read through it and one item stands out and that is this; a Fans off item, "The A/C refrigerant pressure is less than 190 psi (A/C off)."

While it is listed as an OR, I beleive that should be an AND. If the temp is < 220 AND the pressure is less then 190. IOW, when there isn't a need for it to be on, it's off. Otherwise if the car's AC ever went south, the fans would never turn on. Not exactly the best failure mode.

I would look at shorting out F3 and/or C10 to ground. This should energize the relay(s) and turn on the fan. You should be able to hear a click using a mechanic's stethascope. If the fans don't run or you don't hear a click, I'd look at a power issue. If you do hear a click, it's either wiring between the relay and the PCM, or the PCM itself not triggering it.

[dantatara]

I was thinking that (the idea that both conditions have to be present) however I had someone with the same vehicle as mine test this. Had him turn on the AC right after starting (engine cold) and the fans turn on instantly, when the engine is cold. That's why I am leaning the way I am. or a PCM failure. I'll try using the ground approach.

[GregA]

Originally Posted by dantatara

I was thinking that (the idea that both conditions have to be present) however I had someone with the same vehicle as mine test this. Had him turn on the AC right after starting (engine cold) and the fans turn on instantly, when the engine is cold. That's why I am leaning the way I am. or a PCM failure. I'll try using the ground approach.

Dan,

Have you connected BOTH fans directly to power (12 V & Ground)?

Also, there are THREE relays that control the fans (along with the PCM) - you only seemed to mention TWO in your previous post.

If you would like, I can color the schematic to show what should be on for both LOW & HIGH settings. Let me know.

Take care,

[dantatara]

Yes, the first thing I did was run the fans direct and checked ok. I understand the schematic and the 3 relays also. Low speed runs the fans in series with each other and high speed runs the fans with the full 12v each. What I need to do is find the grd wire for both Lo/Hi relays, grd it operating the relays and the fans should work. (I'll probably lift the fuse block out and get at the wiring there) This would narrow the problem to be the PCM or PCM controls. I need drawings showing details going out. For example, PCM details. Question; Where is the AC pressure switch?
Thanks

[GregA]

Originally Posted by dantatara

Yes, the first thing I did was run the fans direct and checked ok. I understand the schematic and the 3 relays also. Low speed runs the fans in series with each other and high speed runs the fans with the full 12v each. What I need to do is find the grd wire for both Lo/Hi relays, grd it operating the relays and the fans should work. (I'll probably lift the fuse block out and get at the wiring there) This would narrow the problem to be the PCM or PCM controls. I need drawings showing details going out. For example, PCM details. Question; Where is the AC pressure switch?
Thanks

Cool (well, not yet temperature, but that you know what to look for).

I tried to get a picture of where the sensor was, but it is way too crowded under the hood, so I put up a drawing (link below). I think it is below the Air Filter housing.

Air Conditioner Pressure Sensor

Good Luck,

[dantatara]

Concluding, (Its been a long time since I replied) First, On the AC; the used car dealer where we just recently purchased it agreed to have there service dept check it out. The system held a vacume fine. Charged it and the AC works like it should. When you turn the AC on now the low speed fan is on. This van has the rear AC also. Will keep an eye on it.
Second, on the temp sensor; What I hear is that the 220 deg range of the sensor operating is so high that the engine rarely gets that hot. If you compare the temp gauge with a clock it has to get to about 2 for the sensor to operate. Mine was as high as about 1 so I thought that was a problem. I guess its all in what you know and learn.

Thanks all for your input. It really helped troubleshoot and I appreciate that. Ya never know, maybe someday I can return the favor.

[cdru]

Originally Posted by dantatara

Second, on the temp sensor; What I hear is that the 220 deg range of the sensor operating is so high that the engine rarely gets that hot.

I wouldn't say that "the engine rarely gets that hot". Normal operating tempature is 195 degrees. As long as your coolant reaches that tempature, it operating fine. Normal driving provides sufficient airflow under most circumstances to maintain that 195 (+/- a few degrees) without the use of the fans. It only becomes a concern when the airflow isn't enough on it's own.