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Aux. Electric Fan 200 1993

posted by  Williston on  Wed Jun 29 10:10 CST 2005
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last visit: Tue Dec 11 14:18 CST 2012
[RELATED]

There have been a few recent posts asking about how often the A/C compressor should cycle on and off. I have a related question about the aux radiator fan:
I notice on my car, the fan is also intermittantly cycling on and off when the AC is on. It usually comes on a few seconds after the compressor after turning on the A/C, but last night when I pulled into the house, I noticed the fan wasn't running even with the A/C on. After 30 seconds or so, it kicked on. Then it dawned on me that it must be doing this as I'm driving along the highway too, since I noticed the headlights and panel lights dim slightly every so often like when a big load is suddenly added. Turn off the A/C and this stops. I figure it has to be the fan kicking in since it draws a pretty big load when it starts. If anyone knows, I'd be interested in hearing what controls this fan and whether this is normal or not. The thing with the lights is a little annoying at night. I had just assumed it would be on continuously when the A/C is on. I'd also like to know if the fan is also thermostatically controlled as well: Will it come on when needed (hot engine) even with the AC off? Thanks!








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    Aux. Electric Fan 200 1993

    posted by  Sumerduckman on  Wed Jun 29 10:41 CST 2005
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    last visit: Tue Aug 21 11:31 CST 2007
    [RELATED]

    Don't know 100% on the later 200 series, but on my 94 940 the radiator fan is controlled by both the temp switch on the radiator and the pressure switches on the ac condenser. The fan cycles on when the ac system high side pressures reach a certain point. And it will cycle when the radiator temps are high enough whether or not the car is on or not.
    If your lights are dimming when it comes on, you should check the condition of the battery, battery cables, battery terminals for corrosion and do a voltage output check on the alternator.
    --
    Gary Gilliam Sumerduck VA, '94 940 na Regina 160k '86 240 190k








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      Aux. Electric Fan 200 1993

      posted by  Williston on  Wed Jun 29 10:52 CST 2005
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      last visit: Tue Dec 11 14:18 CST 2012
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      Thanks for the info Gary. I rather the fan just stay on all the time when the A/C is running. I don't understand the point of having it cycling on and off. As for the lights momentarily dimming: it's very slight and barely noticeable. About the same as when you suddenly switch the interior blower from off to full-on, or turn on the rear defrost and it takes a second for the system to pick up the load.








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        Aux. Electric Fan 200 1993

        posted by  daveshan on  Wed Jun 29 11:58 CST 2005
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        last visit: Sun Oct 19 07:03 CST 2014
        [RELATED]

        The fan draws current which causes a drain on power/fuel economy due to the drag on the alternator. It's pointless to have the fan running while the car is moving fast enough to cool the condensor. This is why it has a pressure switch to turn it on as the pressure in the condensor gets too high indicating insufficient air flow.

        I installed a condensor fan off of a '92 in my '88, it's wired to run all the time when the AC is on, it caused a ~1 mpg drop in fuel mileage on the first tank. This offsets the increase I got by switching to a temp' controled main fan to replace the viscous clutch fan. The '91 on setup is a well designed system as it came from Volvo, they knew what they were doing and I will be having a high side hose made up with ports to add a pressure sensor so I can benefit from the cycling.
        --
        Dave Shannon
        Spring Valley, California
        '67 1800s
        '73 1800ES
        '88-240
        my pages








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          Aux. Electric Fan 200 1993

          posted by  Williston on  Wed Jun 29 12:37 CST 2005
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          last visit: Tue Dec 11 14:18 CST 2012
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          I agree with what you have posted. The issue I'm seeing is the fan is cycling on and off going down the highway at 70 mph. Myabe it's a symptom of something else going on in the system, but the A/C is blowing nice and cold regardless.








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            Aux. Electric Fan 200 1993

            posted by  daveshan on  Wed Jun 29 13:07 CST 2005
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            last visit: Sun Oct 19 07:03 CST 2014
            [RELATED]

            It may also have an engine temp sensor in the loop, my '92 745Ti did, this would cause it to come on under heavy engine loads. Sadly I don't have any green books of a later vintage that would cover your car. Does it cycle in a pattern of hills/acceleration to pass or anything else you notice. Another thing is, if you are assuming it is coming on due to the fluctuations of your lighting, it may well be something else.

            When I was first testing the main fan and trying to select the proper sensor to control it I hooked up a tattletale light to see when it was on and off. It should be fairly simple to tap into the wiring for the condensor fan and do the same to see if it really is cycling on and off or if you have another issue causing the dimming of the lights.

            BTW, I notice no dimming of the lights when any of my fans kick on.
            --
            Dave Shannon
            Spring Valley, California
            '67 1800s
            '73 1800ES
            '88-240
            my pages








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              Aux. Electric Fan 200 1993

              posted by  Williston on  Wed Jun 29 14:23 CST 2005
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              last visit: Tue Dec 11 14:18 CST 2012
              [RELATED]

              Thank you again for the feedback Dave. This car is fairly new to me as I just "retired" my '90 245 at 291,000 miles. I'm still sorting out what is "normal" for this car vs. the '90. I'm not picking up any particular pattern to the cycling, but I do know when I shut off the A/C the cycling and the lighting surge goes away. Also, I'm only getting this occuring on the highway. I think what I need to confirm is whether it's the fan, or the compressor that is doing all the cycling. Which ever it is, sometimes it is pretty frequent: 10-15 secs on, 10-15 secs off. I would suspect a low charge, but the the air out of the vents is nice and cold under any condition: idle, highway or around town. I think I'll start by unplugging the fan connector behind the grill and see what happens. This '93 was a nice find: adult owned and only 90,000 miles on it.








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                Aux. Electric Fan 200 1993

                posted by  Patrick of Mtl on  Wed Jun 29 23:16 CST 2005
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                last visit: Tue Oct 12 23:46 CST 2010
                [RELATED]

                To avoide overheating something why not go the other way and wire it "permanent on" to see if the cycling goes away. I have experienced sensor situations with temp controlled switches that were poorly designed for their function. Basically it seems like an engineer decides that a fan should start at temp X and stop at temp Y without taking into account the system lags behind in actual temp change. I have been known to install switches on my dash to override these functions when neccessary. The trick to this it to wire it so that the auto system still works but you can override it if you want to. Or maybe you have a bad sensor.
                --
                Patrick, '68 220, '83 245, '92 Eurovan (work truck).







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