CX cooling fan switches and relays
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  1. #1
    Too many posts! JohnW's Avatar
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    Default CX cooling fan switches and relays

    No doubt this was all explained pre-crash!!

    My CX has decided to start running on the hot side, and rises to 100 degrees when parked after heavy traffic running. The temp comes down to 95 or so on restarting etc but no further. AFAIK, the low speed fan operation is fine. With the AC running, the high speed fan operation is fine. But when I short circuit the wires on the air-operated temperature switch just behind the radiator, nothing happens. I recall, perhaps correctly, that this switch is used to bring on the high speed fan operations in a 2400 C-matic with AC.

    Does someone know which relay the "air switch" operates to switch on the fans? I would have thought the high speed fan operation relay(s) would be the same and operated the same way by both AC and this high temperature switch. However, this is not so, unless the wires from this switch are not connected at the other end. Does someone know, much the same question, where these two wire go?

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    Or do I have it wrong, and the airflow switch turns on the low fan speed? In this case my wiring is a bit screwed up, but it has not been changed from before.

    The temperature gauge used to sit pretty well rock steady on 85-high 80s but now for no apparent reason sits a bit above 90 and rises closer to 100 in warm to hot driving in stop start traffic. I've checked the thermostat, and it appears to be opening OK, although I'm not exactly sure whether it is opening early enough or far enough. I know, replace it and see what happens. The radiator was fixed thoroughly a few years ago and nothing has been used but coolant since then, so it should be fine. Inlet and outlet hoses from the radiator both feel hot, so it is passing water, so to speak.

    Any suggestions please?
    JohnW

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  2. #2
    1000+ Posts gerrypro's Avatar
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    Earlier CX's with C Matic and air did not have this extra sensor. Mine is like this and seems not to suffer any overheating problems.
    Cheers Gerry

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    Too many posts! JohnW's Avatar
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    Quote Originally Posted by gerrypro View Post
    Earlier CX's with C Matic and air did not have this extra sensor. Mine is like this and seems not to suffer any overheating problems.
    Wow that was quick! I've never had a problem before actually, and it isn't actually boiling, just closer than I'd like to 100 degrees. Does your single sensor turn the fans on full blast or half blast Gerry?

    Of course it could be the gauge, but it has always performed perfectly and is good quality.
    JohnW

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  4. #4
    Now go make me a sandwich Hotrodelectric's Avatar
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    Just to go full tilt boogie John, when was the last waterpump service/replacement? The problem could be as stupid as the cap seal on the overflow tank. I'll have to dig a bit to see how the CX fans wire up. 1980, so we are talking early Series 1.5?
    The measure of your character isn't what you do when people are watching- it's what you do when they aren't watching.

  5. #5
    1000+ Posts gerrypro's Avatar
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    Seems to turn on at just one speed. Maybe this is the reason for the addition of the extra sensor----to provide a more progressive fan suited to the needs of the system???????
    Cheers Gerry

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    Too many posts! JohnW's Avatar
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    Quote Originally Posted by Hotrodelectric View Post
    Just to go full tilt boogie John, when was the last waterpump service/replacement? The problem could be as stupid as the cap seal on the overflow tank. I'll have to dig a bit to see how the CX fans wire up. 1980, so we are talking early Series 1.5?
    Good questions both. The water pump hasn't been touched for a while but hasn't done more than 20-30,000 since replacement. I've no reason to think the cap is faulty, as it certainly holds pressure.

    The car is a narrow track with Diravi, built in 1979, but sales were, well, slow. Imagine competing with an XJ6 Jaguar with full automatic at about the same price...

    I ought to check the back bleed screw too, come to think of it. Of course, I've no idea whether that second, air temperature controlled switch ever worked! You check these things when something goes wrong, human nature being what it is. The previous owners were meticulous, so I expect it worked just fine.

    It isn't overheating seriously, just has "changed" for no obvious reason (not YET obvious, that is). My plan is to head the problem off at the pass.

    Cheers and thanks.
    JohnW

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    Fellow Frogger! andrewj's Avatar
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    Hi John,

    Good luck with it. A quick word of caution - I went through this process with the Red Rocket (1984 2500IE) around 5 years back. Suspected at relay, so swapped in a couple spare ones. Big mistake! The fan control relays have different wiring to a standard horn relay, and as a result I got a hard fault on an unfused circuit when the second thermo switch closed. Completely fried the front loom plus a couple of relay plugs.

    Two days of re-wiring later, everything seemed to come good for no particular reason. Suspect it was a corroded relay plug or something of the sort, but will never really know.

    Hope your experience is less dramatic...

    Cheers,
    Andrew

    Driving - '90 XM, '85 CX IE Auto, 406 Coupe, 405 srdt wagon, '78 dyane, Resting (or Rusting): '73 Birotor '82 CX Presitige, '81 CX Break IE, GS X2, GS1015 Wagon, GS 1300 5sp Wagon, '76 GS 1220 Wagon, '75 GS Wagon, '58 2CV, '58 Vauxhall Velox

  8. #8
    Too many posts! JohnW's Avatar
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    Quote Originally Posted by gerrypro View Post
    Seems to turn on at just one speed. Maybe this is the reason for the addition of the extra sensor----to provide a more progressive fan suited to the needs of the system???????
    I think you are right!
    JohnW

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    Renault R8 1965 (R1130)
    Renault Scenic Series II 2005 (wife's)
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  9. #9
    Too many posts! JohnW's Avatar
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    Quote Originally Posted by andrewj View Post
    Hi John,

    Good luck with it. A quick word of caution - I went through this process with the Red Rocket (1984 2500IE) around 5 years back. Suspected at relay, so swapped in a couple spare ones. Big mistake! The fan control relays have different wiring to a standard horn relay, and as a result I got a hard fault on an unfused circuit when the second thermo switch closed. Completely fried the front loom plus a couple of relay plugs.

    Two days of re-wiring later, everything seemed to come good for no particular reason. Suspect it was a corroded relay plug or something of the sort, but will never really know.

    Hope your experience is less dramatic...

    Cheers,
    Andrew
    Thanks Andrew. Appreciate the warning!

    So. please, where exactly were the fan relays? Do you have part numbers etc by any chance so I buy the right ones if needed?

    You'll have noted I have low fan speed working OK, from the sensor in the radiator, and high speed from the AC, but nothing happening in the circuit from the air-operated sensor.

    You have to love CX wiring around the battery/headlamp area....
    JohnW

    Renault 4CV 1950 (R1062)
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    Renault Scenic Series II 2005 (wife's)
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  10. #10
    Real cars have hydraulics DoubleChevron's Avatar
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    It's years since I've looked at this setup. Grab out a wiring diagram and have a look. You need to understand how it works, it's a simple'ish horrific mess of wiring.

    There is two fans wired series/parallel. Series they share 12volts (ie: 6volts each) so run at slow speed. Parallel is obviously high speed and they each get 12volts. The small sensor in the airflow should switch on low speed fans. Pull the connectors off and join them together. You should get low speed fans.

    Now there is one switch on the radiator, this is high speed fans. Pull this off and join the wires together. If you have only one fan on high speed, and no low speed you have a faulty or disconnected fan (think of how a series circuit works). Try and trace the wiring back to the series/parallel relay. Pull off and check all the relays and look for the burnt one is probably the easiest way. Snip off the relay connector and (cut back into the harness a bit and make sure you get sound wire) then solder in a new relay base. Fit new relay. Just wiggling the relay to get it temporarily working again isn't really a fix (yeah, I've been there and done that many times ).

    seeya,
    Shane L.
    'Cit' homepage:
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  11. #11
    1000+ Posts Greg C's Avatar
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    There is nothing special about the relays. There are two normal and one crossover.

    Your car should have the air temp sensor which will put both fans in series, i.e. low speed. If you short the two wires on the coolant temp sensor on the side of the tank both fans should run in parallel i.e. high speed. If you have been using the air con, it will depend on how much gas is in the system, but over here mine has been running a bit hotter than normal as it has not been hot enough to trip the trinary switch contact and get the fans to high speed. So in traffic the coolant temp slowly builds up to when the coolant temp switch closes and then I get high speed.

    I have never owned an Australian delivered CX but my 1978 was wired so low speed was triggered by the air temp sensor only. I changed that so turning on the Air con triggered that in addition. The Prestige is wired that way from the factory. Much better.

    What is the air operated sensor? Is it what I call the air temp sensor, a little aluminium disc, on a bracket hanging down behind the radiator.
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  12. #12
    Too many posts! JohnW's Avatar
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    Quote Originally Posted by DoubleChevron View Post
    It's years since I've looked at this setup. Grab out a wiring diagram and have a look. You need to understand how it works, it's a simple'ish horrific mess of wiring.

    There is two fans wired series/parallel. Series they share 12volts (ie: 6volts each) so run at slow speed. Parallel is obviously high speed and they each get 12volts. The small sensor in the airflow should switch on low speed fans. Pull the connectors off and join them together. You should get low speed fans.

    Now there is one switch on the radiator, this is high speed fans. Pull this off and join the wires together. If you have only one fan on high speed, and no low speed you have a faulty or disconnected fan (think of how a series circuit works). Try and trace the wiring back to the series/parallel relay. Pull off and check all the relays and look for the burnt one is probably the easiest way. Snip off the relay connector and (cut back into the harness a bit and make sure you get sound wire) then solder in a new relay base. Fit new relay. Just wiggling the relay to get it temporarily working again isn't really a fix (yeah, I've been there and done that many times ).

    seeya,
    Shane L.
    Many thanks Shane. I had some of that right in my mind, but not all!!
    JohnW

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  13. #13
    Too many posts! JohnW's Avatar
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    Quote Originally Posted by Greg C View Post
    There is nothing special about the relays. There are two normal and one crossover.

    Your car should have the air temp sensor which will put both fans in series, i.e. low speed. If you short the two wires on the coolant temp sensor on the side of the tank both fans should run in parallel i.e. high speed. If you have been using the air con, it will depend on how much gas is in the system, but over here mine has been running a bit hotter than normal as it has not been hot enough to trip the trinary switch contact and get the fans to high speed. So in traffic the coolant temp slowly builds up to when the coolant temp switch closes and then I get high speed.

    I have never owned an Australian delivered CX but my 1978 was wired so low speed was triggered by the air temp sensor only. I changed that so turning on the Air con triggered that in addition. The Prestige is wired that way from the factory. Much better.

    What is the air operated sensor? Is it what I call the air temp sensor, a little aluminium disc, on a bracket hanging down behind the radiator.
    Many thanks Greg. Yes, I mean that little aluminium disc. Mine has a low and high speed on temperature, or should have, and high speed as soon as the AC is turned on. The high speed temp switch isn't actuating high speed fan, and I was mistaken about which switch was which.

    Cheers
    JohnW

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  14. #14
    Fellow Frogger! IE23's Avatar
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    I'm sure my fans don't operate on slow speed, I have only noticed the fans come on at reasonably fast speed. Well actually I'm not 100% sure if it's fast or slow! but I'm sure it's one speed only. The same single speed for when the AC is turned on. So I need to do some checking too. I have never notice an air sensor, can someone post a picture so I know what to look for please?


    Adrian

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    Quote Originally Posted by IE23 View Post
    I'm sure my fans don't operate on slow speed, I have only noticed the fans come on at reasonably fast speed. Well actually I'm not 100% sure if it's fast or slow! but I'm sure it's one speed only. The same single speed for when the AC is turned on. So I need to do some checking too. I have never notice an air sensor, can someone post a picture so I know what to look for please?
    If you haven't worked it out by the weekend I'll take a photo. Mine has a standard, screw in temperature switch on the passenger side tank of the radiator with two wires. Then at the top of the radiator, behind the finning, on the passenger side of centre, there are two wires going to a little aluminium cylinder, about 12 mm diameter and as long, with two spade terminals. It sits almost loose within a bracket just behind the fins, pointing into the air flow. I don't think they all have them!

    When you turn on the AC the fans roar in my car.
    JohnW

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  16. #16
    1000+ Posts Greg C's Avatar
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    Adrian, yours is probably not a Grande Exportation model so may not have the series parallel system.
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  17. #17
    Real cars have hydraulics DoubleChevron's Avatar
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    Quote Originally Posted by Greg C View Post
    Adrian, yours is probably not a Grande Exportation model so may not have the series parallel system.
    Same thing ... if he checks the temperature switch on the radiator, it'll have 3terminals. ie: The temperature switch is a low and high speed switch all in one. Same deal with series/parallel. He's probably just never noticed the fans when there running at low speed as they are quiet (either that or one fan is dead, so he has one fan working on high speed, and no low speed).

    seeya,
    Shane L.
    'Cit' homepage:
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    '85 Series II CX2500 GTi Turbo I
    '63 ID19 http://www.aussiefrogs.com/forum/showthread.php?t=90325
    '72 DS21 ie 5spd pallas (last looked at ... about 15years ago)
    '78 GS1220 pallas
    '92 Range Rover Classic ... 5spd manual.

    Yay ... No Slugomatics


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    Quote Originally Posted by DoubleChevron View Post
    Same thing ... if he checks the temperature switch on the radiator, it'll have 3terminals. ie: The temperature switch is a low and high speed switch all in one. Same deal with series/parallel. He's probably just never noticed the fans when there running at low speed as they are quiet (either that or one fan is dead, so he has one fan working on high speed, and no low speed).

    seeya,
    Shane L.
    Both fans run at one speed only, I have seen and checked this many times due to replacing the water pump & radiator & new thermo switch myself on separate occasions.

    The mighty CX is away having the roof attended to, so I can't check it right now, but will next opportunity.


    Adrian

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    Quote Originally Posted by JohnW View Post
    Thanks Andrew. Appreciate the warning!

    So. please, where exactly were the fan relays? Do you have part numbers etc by any chance so I buy the right ones if needed?

    You'll have noted I have low fan speed working OK, from the sensor in the radiator, and high speed from the AC, but nothing happening in the circuit from the air-operated sensor.

    You have to love CX wiring around the battery/headlamp area....
    Hi John,

    I must admit I was doubting my sanity after reading Greg's post. Having dug through the wiring diagrams, it seems I managed to replace the "cross over" relay with a normal open relay with twin "87" pins. A bit embarrassing really

    So I guess the lesson is, check the spec of the relay, or if it is out of the spare bits and pieces box, pop the top off to confirm what sort it is!

    Cheers,
    Andrew

    Driving - '90 XM, '85 CX IE Auto, 406 Coupe, 405 srdt wagon, '78 dyane, Resting (or Rusting): '73 Birotor '82 CX Presitige, '81 CX Break IE, GS X2, GS1015 Wagon, GS 1300 5sp Wagon, '76 GS 1220 Wagon, '75 GS Wagon, '58 2CV, '58 Vauxhall Velox

  20. #20
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    Quote Originally Posted by andrewj View Post
    Hi John, I must admit I was doubting my sanity after reading Greg's post. Having dug through the wiring diagrams, it seems I managed to replace the "cross over" relay with a normal open relay with twin "87" pins. A bit embarrassing really So I guess the lesson is, check the spec of the relay, or if it is out of the spare bits and pieces box, pop the top off to confirm what sort it is! Cheers, Andrew
    Thanks Andrew, really appreciate the comments. I'll work out what you mean by a "cross over" relay when I actually tackle it in May. Can you remember, by chance, WHERE the particular relays were located please?
    JohnW

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    Quote Originally Posted by JohnW View Post
    Thanks Andrew, really appreciate the comments. I'll work out what you mean by a "cross over" relay when I actually tackle it in May. Can you remember, by chance, WHERE the particular relays were located please?
    Hi John,

    They are behind the port headlight, in front of the battery. This probably doesn't help much, as there a lot of relays there.

    I'm back home on Friday, so I'll take a photo of the wires - you might (and I stress "might") be able to work out which is which from the wire colours.

    Cheers,
    Andrew

    Driving - '90 XM, '85 CX IE Auto, 406 Coupe, 405 srdt wagon, '78 dyane, Resting (or Rusting): '73 Birotor '82 CX Presitige, '81 CX Break IE, GS X2, GS1015 Wagon, GS 1300 5sp Wagon, '76 GS 1220 Wagon, '75 GS Wagon, '58 2CV, '58 Vauxhall Velox

  22. #22
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    Quote Originally Posted by andrewj View Post
    Hi John,

    They are behind the port headlight, in front of the battery. This probably doesn't help much, as there a lot of relays there.

    I'm back home on Friday, so I'll take a photo of the wires - you might (and I stress "might") be able to work out which is which from the wire colours.

    Cheers,
    Andrew
    Thanks Andrew.

    That narrows it down a bit. Being at times a tad contrary, the car today reverted to its normal running temperature. I'm wondering whether the thermostat was a bit sticky from lack of use and has freed up after a week or so of daily driving... Mary, Mary quite contrary etc etc.

    I do need to sort things from first principles though, since the high speed fans only come on with AC, and am really grateful for the inputs.

    Cheers
    JohnW

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  23. #23
    1000+ Posts Ken W's Avatar
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    John,

    Some of the relays are also on a bracket under the headlight - I think the air temp relay and the aircon relay . The cross over relay is up behind the battery and needs to be in really top notch as it operates under a lot of high current and switching pressure. You need to keep the low speed air temp control shorted when you short the radiator temp sensor or you will only get one fan to operate at high speed. My aircon has a relay in parallel with the air temp sensor to bring the fans on when aircon compressor is engaged and then you let the radiator sensor take it to high speed as per normal.

    As for the running hot, can you see the thermostat open on your temp gauge? On mine the temp peaks a little before dropping as the thermostat opens. Maybe the thermostat temp has gone a bit high - it should be around 80 degrees C. Or else maybe you need a radiator flush or clean out.

    One of the circuit diagrams in the Haynes manual sort of has this wiring arrangement shown, I will look up the page number for you tonight.

    Cheers,

    Ken W

  24. #24
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    Quote Originally Posted by Ken W View Post
    John,

    Some of the relays are also on a bracket under the headlight - I think the air temp relay and the aircon relay . The cross over relay is up behind the battery and needs to be in really top notch as it operates under a lot of high current and switching pressure. You need to keep the low speed air temp control shorted when you short the radiator temp sensor or you will only get one fan to operate at high speed. My aircon has a relay in parallel with the air temp sensor to bring the fans on when aircon compressor is engaged and then you let the radiator sensor take it to high speed as per normal.

    As for the running hot, can you see the thermostat open on your temp gauge? On mine the temp peaks a little before dropping as the thermostat opens. Maybe the thermostat temp has gone a bit high - it should be around 80 degrees C. Or else maybe you need a radiator flush or clean out.

    One of the circuit diagrams in the Haynes manual sort of has this wiring arrangement shown, I will look up the page number for you tonight.

    Cheers,

    Ken W
    Thanks for the clarity Ken. Much appreciated. Mine has always brought the high speed fans on when AC is used - the previous owners did modify a few things electrically and no diagrams of course....

    She was contrary today! Morning, 12 degrees, and the temp guage sat around 85, in exactly the place it has occupied for years. It rose above there until the thermostat opened then dropped back. Perfect. Then in the afternoon, going to an airport pickup and I guess 25-27 degrees, it just kept rising and nudged 95+, but in stop-start traffic (love the C-matic at times like that) approached 100 once, then dropped. Then on the way home, a bit later and cooler, it was just over 90, towards 95 again, sitting on 80-100 kph on main roads and freeway. In Perth it's "THE freeway"!

    It all smacks of restricted coolant flow to me, and somewhat inconsistent behaviour does point first to thermostat, albeit not uniquely. The radiator was rebuilt a few years back, having split dramatically one morning. The C-matic heat exchanger similarly. Nothing has ever been used but coolant, so it is hard to imagine the cooling system is clogged anywhere, but maybe it is. The thermostat opens with boiling water but I haven't, and should have, tested its opening temperature more thoroughly.... the coolant was fine and no sign of dirt in the thermostat area when I pulled it out last week.

    I do wonder whether the airflow sensor that is meant to turn on low speed has been swapped with the one in the radiator tank. I do get low speed fans, but when they aren't on, shorting that little alloy button terminals doesn't seem to do anything. This could mean that the low speed fans are coming on too late, switched at the tank sensor and the high speed ones not at all. That makes no sense - why bother to change them.

    We're off to Q'ld with the Renault club there over Easter, so I'll tackle this in May unless strongly moved to do it over the weekend! I'll start with a new thermostat I reckon. Not exactly a hard job and the type is available round the corner!

    Cheers
    JohnW

    Renault 4CV 1950 (R1062)
    Renault R8 1965 (R1130)
    Renault Scenic Series II 2005 (wife's)
    Renault Scenic Series II 2006 (daughter's)
    Renault Scenic Series II 2007 (mine)

    CitroŽn CX Pallas 1980 (moved on to new custodian)

    National Co-ordinator, Renault 4CV Register of Australia

  25. #25
    1000+ Posts Ken W's Avatar
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    John,

    Checkout Fig 13.53 which is on page 254 in my Haynes CX manual. It is for the Prestige 1978-79 but has the circuit showing the two speedradiator fans integrated in with aircon on the left hand side.

    Cheers,

    Ken W

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