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Old 05-31-2021, 01:02 PM   #1
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Default Radiator Fan Linked to A/C?

Just curious if the radiator fan is linked to the A/C system. I've noticed that the fan on the car doesn't turn on, though it isn't actually overheating either.

When I was initially testing the A/C to find out why that wasn't running, I could jump the circuit at the pressure switch and turn it on manually.

So, does that mean the radiator fan only turns on when the A/C is pressurized and running?
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Old 05-31-2021, 01:21 PM   #2
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Default Re: Radiator Fan Linked to A/C?

The radiator fan should come on when either the engine temp is hot enough (about 210F) or the A/C is selected to be on (at any temp).

I forget what year your car is, but the fan will also come on when jumpering the ALDL to look for "blinky codes" on a gen1.

I don't think the A/C (or compressor) has to be operating properly for the rad fan to come on, just having the cabin controls set for A/C enables the fan.

There is no direct link between the A/C and fan, it is all through the PCM/BCM.
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Old 05-31-2021, 02:39 PM   #3
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Default Re: Radiator Fan Linked to A/C?

Ok, I'll look into it further. I'll have to run Live Data again and see where the engine temp gets to also.

Was just curious because I had a '95 Grand Prix that was wired in such a way that if the A/C wasn't operational, the radiator fan wouldn't kick in even if the car was overheating. Awesome work there, GM.
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Old 05-31-2021, 02:47 PM   #4
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Default Re: Radiator Fan Linked to A/C?

Did you buy that Pontiac brand-new, from the dealer? I think that wiring had been modified, no manufacturer would design/build engine cooling like that.
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Old 05-31-2021, 02:52 PM   #5
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Default Re: Radiator Fan Linked to A/C?

No, bought used, but there was no re-wiring done to the fans (you could tell if there were). I asked about it on a forum years ago and someone said that all the mid 90's Grand Prix's were like that.

I also found out the wiring in those specific cars were woefully under gauged. If you were driving at night (in winter) with the heat on high, wipers going, rear defrost, all lights on, and a turn signal blinking, the voltage would drop from 13.9 to about 12.5. It was enough that if you placed your foot on the gas to raise the RPM's 100-200 more, everything would light up bright. They said that if the alternator pulley was just a hair bigger in diameter, that would have also solved the problems.

Gotta save money somewhere, right? *facepalm*
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Old 05-31-2021, 04:47 PM   #6
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Default Re: Radiator Fan Linked to A/C?

Saturns turn on cooling fans when ac runs. However, cooling fans do not run if the ac system fails. You're not alone in attempting to understand how ac and cooling fans operate. Basically, your ac system suffered the same failures 98% of all vehicle ac system failures - the leak no one wants to address but will refill...............a leaking system.

The ac pressure sensor does only one job, protect the compressor against self destruction when a sealed system loses its refrigerant. Refrigerant circulates along with oil and dye, returning to the compressor for automatic lubrication. Oil misting occurs when high pressure liquid refrigerant is released into the evaporator coils. Loss of refrigerant is detected by the pressure sensor, sends a ground signal to the bcm. The bcm sends a signal to the hvac control panel and to the pcm. The pcm receiving this signal disables power to the compressor.

When loss of refrigerant occurs, less oil returns to the compressor. Allowed to continue running without oil lubrication, the compressor self destructs quickly. Some may hear noises from the compressor before power is disabled by the pcm. When the pcm disables compressor power, it also disables cooling fan operation. When ac is running, the compressor discharges hot refrigerant into the condenser coil (in front of the radiator) so fan cooling is needed to force airflow thru a hot condenser coil and radiator otherwise the cooling system will overheat. If ac fails to run, fan cooling isn't needed. However, fan operation isn't completely disabled as the coolant sensor still detects hot coolant to signal the pcm when to run the fan. Coolant temps are still regulated with the t-stat and coolant sensor.

The cooling fan is enabled by two separate circuits; ac when needed and cooling system when regulating coolant temps. Ac over rides cooling system but only if sufficient refrigerant remains with the compressor running since two radiators are producing heat. With ac off or damaged, the cooling circuit still monitors coolant temps to enable/disable cooling fan operation.

When you jumpered the pressure sensor, all you did was bypass safety, enabled compressor operation and fan. Your ac system lost refrigerant so the sensor safely disabled compressor operation. It's not advisable to continue running the compressor this way as it will self destruct from lack of oil lubrication.
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Old 05-31-2021, 06:19 PM   #7
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Default Re: Radiator Fan Linked to A/C?

lol, this is why I'm trying to learn. I had that Grand Prix with the weird fan, other cars I've had the fan works fine and if it was a truck, it was a clutch fan, so I haven't had much experience trying to figure out faulty fan issues.

I haven't actually gotten the A/C itself to engage, even when I recharged it. I only got as far as the pressure switch, so I still have to diagnose the actual clutch and the power leading up to it.

That was why I was wondering if the fan was tied to the A/C, now I know to look elsewhere
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Old 05-31-2021, 07:16 PM   #8
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Default Re: Radiator Fan Linked to A/C?

Ironically, I found Richpin's video about this exact problem that I'm having. He said to unplug the coolant temp sensor and start the car. If the fan turns on with the sensor unplugged then that eliminates all the other wiring issues because the computer isn't getting the right info from the sensor and just runs the fan all the time to keep the engine cool.

Also going to replace the plug too, it's looking pretty nasty and Richpin says that could also cause issues.

This might also be why my A/C isn't turning on (besides the fact that it's leaking, but that's a whole other issue)
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Old 05-31-2021, 07:35 PM   #9
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Default Re: Radiator Fan Linked to A/C?

Read my reply again. There's a lot of info for anyone unfamiliar with vehicle ac systems. You're under the assumption that something is preventing the cooling fan from running and haven't understood technical explanations given. The fan isn't running because ac is dead. Ac is dead because the system leaked somewhere, losing pressure. The pressure sensor detected lower than ideal pressure and sent a signal to the bcm, sending the signal to the pcm to prevent the cooling fan from running while disabling power to the compressor clutch coil. It doesn't get any simpler than that. The cooling fan still runs for the cooling system.

The short answer is; use an inexpensive uv blacklight to find the source of the leak, repair whatever it takes to return the system to a sealed condition against future leaks, and ac will run along with the cooling fan. Normal standby pressures are close to outside temperatures. 75F/75psi, 85F/85psi, 95F/95psi. All pressures are above the 40 psi trigger point of the pressure sensor. When a sealed system holds refrigerant without leaking, the pressure sensor won't send the disable signal.

If you are seriously interested in how vehicle ac operates then either subscribe to alldata or Mitchell for online service manual info instead of hearsay. If ebay has used service manuals, buy 'em. Ac repairs are unforgiving of mistakes. I use service manuals for reference when posting replies and if possible, wiring diagrams. Technical descriptions can be a page or several pages and posted as pdfs when possible. Some searching within these forums should reveal info if interested. Vehicle refrigeration can be as difficult as EFI systems if not familiar with them on an advanced level. Second guessing can be costly with mistakes learned the hard way.
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Old 05-31-2021, 07:47 PM   #10
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Default Re: Radiator Fan Linked to A/C?

I got what you said, but knowing that the fan is separate from the A/C and that it should be running regardless of whether the A/C is operational or not made me look elsewhere and now it seems to be a faulty coolant temp sensor.

The A/C can wait for a later date, I just needed to know where to start looking for the fan specifically and THEN I'll get back to the A/C because right now, getting the cooling fan operational is far more important than having running A/C. This is why I wanted to make sure whether they were tied together or not, now I don't need to worry about making sure the A/C works.

I also did try to look with a UV light, but I didn't see any dye from previous times the system may have been charged from the other owners and the can I used did not have any UV dye because no one in my area had any in stock at the time I was checking things out.

So, I simply bought a cheap can to at least see if it was keeping up pressure or not and it is not. Now I know I have a leak and when I can get a can that has UV dye in it, I will check again for leaks with the UV light.

Anywho, purchased the new coolant sensor and plug, will have it installed tomorrow. The end of the plug was kind of wet and there was some coolant around the end of the sensor itself where the plug attaches, so it's probably causing all sorts of weird things to happen that it shouldn't.
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Old 05-31-2021, 09:37 PM   #11
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Default Re: Radiator Fan Linked to A/C?

Ok, ac isn't a priority but you're on the right track about a wet coolant sensor. The original is most likely the round nosed one and fails on almost every S-series engine since '91. See below. The faulty one cracks, leaks coolant and tends to ruin the tiny two wire connector requiring replacement of the connector and wires. The circuit operates on 5vdc so any corrosion can alter signal output. The best way to assess the coolant circuit is with a reader displaying sensor/pcm signals.

Baseline reference is coolant sensor measuring cold engine temps at ignition on time and should be close to outside temps. After startup, temps should rise until ten minutes of idling or driving to show between 185F-200F. Since you cannot tell if the t-stat (usually running cooler) or coolant sensor failed (both do), the reader display can be misleading. In all cases, remove the coolant sensor and examine it. Replace it with the flat nosed brass sensor. This should be first so the pcm can have reliable signals. The connector, if wet, may still work by flushing it with alcohol or carb cleaner then dabbing it dry on a rag or napkin. Once replaced, the engine should exhibit typical EFI instant startup without touching the gas pedal, summer or winter. Once coolant temps are seen with a reader, either normal operating temps are reached or its lower. Lower than 185F, replace the t-stat.

As mentioned, the cooling fan turns on at around 220F (seen best with a reader). Temperature gauge needle should be between the 1/4 and 1/2 marks.

Some inexpensive uv lights may not be bright enough. The vehicle should be examined in a dark garage or at night for best illumination of dye. Even a 20 year old car has dye in the system since its mixed in with oil. Dye doesn't fade in oil. Once refrigerant oil and dye leaks or released to the atmosphere, dye remains for several weeks on surfaces since oil takes time to dry out. It's not absolutely necessary to install refrigerant with dye but that's a personal decision. Examples of dye should be on service valves with oil tinted a light green. Search carefully, under and over the engine on every part of the ac system. If you're lucky, the service valves may be the source of the leaks and simply replacing them with new valve cores. If the system still has pressure, borrowing a valve core replacement tool from Autozone allows pressure to remain in the system while removing and replacing each valve core.
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File Type: jpg ac valve core tool.jpg (25.7 KB, 3 views)

Last edited by fdryer; 05-31-2021 at 09:52 PM.
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Old 05-31-2021, 10:05 PM   #12
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Default Re: Radiator Fan Linked to A/C?

Yeah, I had replaced the thermostat and flushed the entire system as well because it was always running cool. It was after I replaced the thermostat and coolant and when it got up to operating temp that I noticed that the fan would never come on. My suspicions were verified when I was sitting in a drive-thru and the needle slowly crept up to the half way mark between C and H. It didn't seem to go any further than that, but I was sure the fan would kick in during that, but since I was on the road, I didn't have a chance to take out my scanner to check the coolant temp to see if it reached 220.

I did wait until it was dark out to check for any dye, but I couldn't seem to locate any. I'll get a can with some dye in it and try it that way too and get more thorough with the A/C after I get all these other minor things taken care of. I still have a possibly faulty TPS that I need to test yet and a tranny mount to replace.

I did note that there was a paint mark on the top of the radiator support that said "A/C 5-18", that tells me someone had it running at some point or at least tried to service it, but between then and now it has stopped working (along with a couple other paint marks stating "Coolant 9-17" and "A-F Trans Service 2-17"). No way to know and I'm not worried about what it could possibly mean since it's just not working.

This car never had it so good until I got it
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Old 06-01-2021, 12:47 AM   #13
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Default Re: Radiator Fan Linked to A/C?

Until you get it sorted out and replace the ECTS and wiring (if needed) you can create a manual fan switch with the AC button.

Simply disconnect the compressor connector, then put a jumper on the AC pressure switch. With those two things done, you can manually turn your fan on by turning on the fan and pushing the AC button to the on position.

Until you get your AC working, you can actually leave this in place with the ECTS fixed as well. That way if stuck in stop and go or a long drive through you can give it a blast before the temp gets way up, and you will have a larger cooling reserve with the radiator coolant already cooled down.
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Old 06-01-2021, 02:44 PM   #14
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Default Re: Radiator Fan Linked to A/C?

Ironically, the fan seems to be working fine. I got home today and let the car sit and idle for a bit with my scanner hooked up and sure enough, the temp hit 221 and the fan kicked in. I just thought it was odd because I've had cars before where the fan turns on much sooner than that. It look about 3 minutes to get to that temp.

I'm just not sure if that was the way it always was or maybe because I unplugged it to test it, but either way it's working. I'm still going to replace the temp sensor and plug, I'm sure the car can only benefit from it, right?
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Old 06-02-2021, 09:06 PM   #15
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Default Re: Radiator Fan Linked to A/C?

Parts came in today, got out and swapped the sensor with a new one and replaced the plug too. Everything is working just fine. The end of the old sensor was indeed cracked, even though it seemed to be ok, but now I won't ever have to worry about it!
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