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Electric fan wiring options


cbolt

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In order to minimize my A/C compressor issues my installer recommended I install an electric fan that would kick on whenever I have the A/C on regardless of engine temperature. Same installer did that on my other car and my A/C compressor has not failed in a few years however that car will gradually keep getting hotter and hotter engine temps when traveling at 70+ mph, which I suspect is a result of the electric fan causing a disruption of airflow through the radiator at highway speeds when the fan would be unnecessary. I simply cannot have that same condition happen on my Monte because I like to drive long distance in it and don't need to be worried about overheating on the interstate just keeping up with the flow of traffic. That brings me to my question, is there a way to hook up my electric fan to both the thermostat, the A/C switch, and have it cut off when the pressure in the A/C system is normal, or do I have to do one or the other? Can I install a cut out switch for the times when I am cruising along at 75mph and the electric fan is not necessary so the radiator gets proper air flow to keep the engine cool? Has anyone done this kind of thing before? 

 

I have been researching it and really don't see a schematic that would allow the cut out at speed. They all seem to be either a switch and the engine temp sender, or the engine temp sender and the A/C high pressure switch, but not all of the above. 

 

Any help or suggestions from folks who run an electric fan and drive at interstate speed for any length of time is appreciated. Thanks

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Any chance you have some electronics like EFI or Dakota Digital dash in the car? I could see a way to possibly get a signal to trigger the fans off at a certain speed, but would probably need a higher end system than a Sniper or equivalent. 

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No. I have a NA car with analog gauges. I would be satisfied just to be able to flip a switch and have the fan kick off but that doesn't seem realistic if I also want it to come on with the a/c on AND at 185 degrees of engine temp. 

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Do you only have electric fans? Are you running dual electric fans or a single? Are the fans in a shroud? In my LS swapped truck the fans are set to come on one at 210 and one at 220 ( LS like to run hotter) I trick one of them to come on with the AC no matter the temp. With the AC off and running down the road the electric fans do not even come on. In you case you may be able to put a high pressure switch inline with the fan so that it only comes on when the high side pressure gets above the set point like the factory AC cars do, going down the road the air flow across the condenser should keep the high side low enough that the fan does not run.

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If you don't mind using a simple approach like a toggle switch as stated, sure it would work to kill the fans at highway speeds. I'd put it on the coil side (low current feed to trigger relay) of the fan relay to keep fans off whenever you want. Downside would be if you forget to switch it back on after you slow down, the engine would start to overheat.

Simple solution to use as a test as well to see if that's really your problem, or there's something also wrong with your cooling system. Examples could be restricted airflow such as dirty radiator & condenser fins (see that happen a lot), fans just not sized right (unlikely if it cools real good in traffic), shrouding issues, etc.

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Dragcat, I don't have a trinary switch.

Ian, I have installed the single 16" electric fan in conjunction with the factory clutch fan and stock shroud. What you describe would be ideal, the fan doesn't even come on unless the pressure exceeds a certain amount and I guess the installation of a high pressure switch would seem my best option. 

Joe, sometimes the simplest approach is the best one. If I forget to turn the fan on when I am sitting in traffic the stock set up, belt driven clutch fan, should still keep the engine cool but I would have to remember because the electric fan would be necessary to keep the airflow going with the A/C on at idle. Ugh. Decisions, decisions. 

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FWIW, I have A/C on my 72, with a 454 LS6, factory belt driven clutch fan, no cooling issues, and the A/C blows cold no matter if idling, or cruising. There is a good sized Griffin Aluminum radiator installed, but nothing else. It is a R134a system with a Sanden compressor though, but  a factory type system, not an add-on style.

Is your fan clutch working, old, the thermostatic type?

Could be something simple like that, and with all the highway driving you do, I'd still maybe blow out or flush the rad & condenser from the back side to get those bugs and crap out of there. You'd be amazed at the amount of stuff that's going to be in there & how many vehicles I've 'repaired' with just that simple (and free) procedure. You can use compressed air or a water stream (or both).

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Its a brand new compressor on my 134a system, which seems to work fine, however when I got the new compressor installed the A/C tech told me there was something going on with it (his words) and the pressure went up too high just a little above idle so he recommended an electric fan for whenever the a/c was running. That is what started me on the research trail and when I asked again the tech admitted that when rolling down the road and with good airflow over the coils the fan should be unnecessary but he couldn't say for certain. 

 

All that led me to question whether, in the shop at 0 mph there would be no airflow across the coils therefore the pressure would rise but wouldn't rise if the car had proper airflow at highway speeds. Additionally, wouldn't the high pressure switch prevent the system from going too high and cut the compressor off in that event? 

 

In hindsight I would say that if my system was functioning properly I wouldn't have to worry about installing an electric fan, but the a/c tech was pretty adamant that my compressor would die again without one. I am inclined to believe him because I have been to back to back EM's with a frozen and useless a/c compressor. 

 

Ugh. 

 

My fan clutch seems to be working fine as the car has no cooling issues either at idle or at highway speeds in the heat of the Florida summer. Just the a/c seems to be the repeat victim to the heat. That's why I am here for help.  

 

Oh, the condenser is fairly clean and the system was serviced and the receiver/dryer and orifice tube were changed and the system was flushed and vacuumed before the replacement compressor was installed. Its a Pro6ten compressor. If this one fails I will most likely switch to the Sanden, but that means changing the mounts and brackets too. 

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1 hour ago, cbolt said:

Its a brand new compressor on my 134a system, which seems to work fine, however when I got the new compressor installed the A/C tech told me there was something going on with it (his words) and the pressure went up too high just a little above idle so he recommended an electric fan for whenever the a/c was running. That is what started me on the research trail and when I asked again the tech admitted that when rolling down the road and with good airflow over the coils the fan should be unnecessary but he couldn't say for certain. 

If the pressure was going too high there is issues with airflow at idle or he has too much freon in the system, or there is a restriction on the high side. I use this chart when charging non factory systems. What is you idle speed at when the AC is on? A good working mechanical fan should pull enough at idle. 

All of that being said, if you wire in a trinary switch like we have been talking about it would solve most of the issues. Being a AC tech I would love to see the gauges with it running :) 

E72F6CD0-2981-463F-8DDF-5768C3C2D95E_4_5005_c.jpeg

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I am going to take it to a buddies house later this week and put the gauges on it to see what the pressures are because I have no idea and am just going by what the tech told me. 

 

Oh, and I don't have a tach so have no idea what the idle speed is. 

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1 hour ago, cbolt said:

I am going to take it to a buddies house later this week and put the gauges on it to see what the pressures are because I have no idea and am just going by what the tech told me. 

 

Oh, and I don't have a tach so have no idea what the idle speed is. 

If you were closer I would be glad to help. I love figuring these kinds of issues out. Make sure to keep us updated :) 

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On 8/10/2022 at 8:14 AM, cbolt said:

In order to minimize my A/C compressor issues my installer recommended I install an electric fan that would kick on whenever I have the A/C on regardless of engine temperature. Same installer did that on my other car and my A/C compressor has not failed in a few years however that car will gradually keep getting hotter and hotter engine temps when traveling at 70+ mph, which I suspect is a result of the electric fan causing a disruption of airflow through the radiator at highway speeds when the fan would be unnecessary. I simply cannot have that same condition happen on my Monte because I like to drive long distance in it and don't need to be worried about overheating on the interstate just keeping up with the flow of traffic. That brings me to my question, is there a way to hook up my electric fan to both the thermostat, the A/C switch, and have it cut off when the pressure in the A/C system is normal, or do I have to do one or the other? Can I install a cut out switch for the times when I am cruising along at 75mph and the electric fan is not necessary so the radiator gets proper air flow to keep the engine cool? Has anyone done this kind of thing before? 

 

I have been researching it and really don't see a schematic that would allow the cut out at speed. They all seem to be either a switch and the engine temp sender, or the engine temp sender and the A/C high pressure switch, but not all of the above. 

 

Any help or suggestions from folks who run an electric fan and drive at interstate speed for any length of time is appreciated. Thanks

You might look at a Dakota Digital fan controller for this project. Out of the box you can wire it to turn off at a certain temp....such as might be seen during highway driving.  As the water temp goes down from increased air flow on the highway the controller will turn the fan(s) off at a temp you preset. The device also has an optional connection that will turn on the fan(s) whenever the A/C is turned on regardless of the water temp.

I have not investigated how these two features function together but there might be an answer for you using the Controller. IMHO worth a look t least.

I am not a fan of manual switches anywhere in the cooling system. It is IMHO just too easy to switch something of and forget to turn it back on when the need arises. You are asking for an overheat issue if you turn it off on the highway then reenter city driving and forget to flip the switch manually back to the "fan on" position. 

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3 hours ago, Ian said:

If you were closer I would be glad to help. I love figuring these kinds of issues out. Make sure to keep us updated :) 

Jim, how about a road trip to Arkansas to let Ian take a look at it, you and Linda love road trips in the Monte.

rob

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Rob, that is not out of the question at all, the road trip to Arkansas. I may wait until the winter months however. 

 

someone showed me the digital fan controller last night at the local cruise in. I like the fact you can adjust it and it looked super easy to hook up. The downside to his set up was he admitted that his car does still run hot at highway speeds and speculated his radiator and condenser were too close together which prevents any cool air from passing thru the radiator, only the hot air from the condenser. Of course this was just a theory, but anything that would potentially make the car run hot at highway speeds is not for me. I like the extended road trips too much to give that up for around town drivability. 

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My ‘70 came with a huge Ron Davis aluminum radiator and dual electric fans. Fans kick on at 185/190 degrees or run continuously if the AC is on. I haven’t driven it long distances on the expressway to see if airflow at speed/turbulence disrupts cooling. 

But as Joe mentioned, the previous owners mechanic installed a toggle switch on the dash under the steering wheel and out of sight. One position runs the fans all the time, one position runs them off temperature/thermostat/when AC is on, and one position turns them off completely.

And also as Joe cautioned, I was wondering why my fans weren’t kicking on when I drove the car home from the trim shop after the new interior was installed. The installers must’ve pushed the switch to ‘OFF’ at some point crawling under the dash. Luckily I was cognizant enough to be listening for them to kick on as I watched the temperature gauge climb. But they are definitely worth their weight in gold as the temperature drops almost immediately. 

Interesting side note:  The first time my dad came over to see the car, he was hovering over the motor, checking things out while it was running.  He almost jumped out of his skin when those fans kicked on 🤣.  They definitely sound “all business”, almost like an angry swarm of bees when you first hear them.  

 

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