BX Heater control woes
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  1. #1
    Tadpole
    Join Date
    Sep 2005
    Location
    Adelaide, SA
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    5

    Default BX Heater control woes

    Hi all,

    Just bought a BX (1986 19GT) and have some problems with the heater controls.

    1. The fan only works on max, and nothing in between...

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    2. The fan, when on max, turns off when the temperature control is moved away from full cold.

    3. The vent selectors are not working..... Air only comes out of the dash vents regardless of the positions of the lever.

    4. The air recirculation switch on the center console does absolutely nothing.....

    Any suggestions as to where to start troubleshooting?

    Thanks!

    Wilson.

  2. #2
    Fellow Frogger! ajpolden's Avatar
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    Apr 2004
    Location
    Launceston, Tasmania
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    291

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    G'day and welcome to Aussiefrogs and the world of BX19GT ownership. Top car in my opinion, all simple mechanics, no fuel injection, ECUs etc. to worry about (just a carby that plays up if you dont change the fuel filter often enough )
    The electrics on my car have been mucked around with a few times - one reason why I am reluctant to take it anywhere near an auto sparky unless I know they do quality work. Makes it difficult for a wannabe DIYer such as myself

    1) Your first problem, there is a fan control unit of some description just above your foot pedals, nearest to the brake I think. This device should have two wires coming off it. I had accidentally kicked mine off at some stage (I think that's what I did) and the fan only worked on the max setting.

    2) As far as I know this is supposed to happen. I can't remember, but I can check back later to see if it is something I had fixed. EDIT: Now that I think about it, the air con is disabled by a small switch in the temp slider mechanism, I think it may also affect the max blower speed setting. Whatever the case, I'm sure fixing (1) will solve it.

    3) Haven't come across this one. The vent is controlled with a cable in the mechanism behind the heater controls, which has probably come loose. I've had this section apart hundreds of times, fixing radio/fan problems, and just general playing around with the wiring. If you need help if the Haynes workshop manual isn't enough, just ask me, I'll try to help.

    4) This is a fairly complex one, common also on a series one BX16TRS (I think). I fiddled for ages trying to fix this, came to the conclusion that the wiring was OK. I then traced the problem to the little servo motors attached to the vent flaps. After pulling them off (no small task) I found that they had both suffered corrosion - one to a much lesser extent than the other.
    I doubt you could buy these new these days (but I didn't try), so unless you can find a wreck with these in a good working state, I doubt you could actually replace them. I managed to repair them both, but it took a while, and as I said it's quite complex. If you're prepared to tackle it, I'll post more details.

    Hope this solves most if not all of your car's issues you mentioned
    Andrew..
    Last edited by ajpolden; 30th September 2005 at 10:04 PM.
    Current:
    1999 406SV (D8)
    Previous:
    1986 BX19GT

  3. #3
    Too many posts! JohnW's Avatar
    Join Date
    Jul 2001
    Location
    Perth, WA, Australia
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    10,800

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    Quote Originally Posted by quattro920
    Hi all,

    Just bought a BX (1986 19GT) and have some problems with the heater controls.

    1. The fan only works on max, and nothing in between...

    2. The fan, when on max, turns off when the temperature control is moved away from full cold.

    3. The vent selectors are not working..... Air only comes out of the dash vents regardless of the positions of the lever.

    4. The air recirculation switch on the center console does absolutely nothing.....

    Any suggestions as to where to start troubleshooting?

    Thanks!

    Wilson.
    I have a different BX (19TZi) with AC and no doubt slightly different heater controls. However, on this forum somewhere there is a thread on the problems I had about a year ago. There may be other threads too if you search and, if you go to the Andyspares forum and search there, you'll find quite a bit of advice on the BX fan printed circuit board, again which might help.

    Best of luck.

    JohnW

  4. #4
    1000+ Posts Ken W's Avatar
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    Sep 2002
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    North Brisbane
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    1,928

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    Wilson,

    Just came upstairs from fighting a interior fan speed problem in a BX 16Valve - haven't won yet. Max speed will not work and it looks like it isn't wired to work even though the relay is there.

    Now over to your problem - all BXs interior fans seem to work similarily but there are some detail defferences between the models relating to how the switches and relays are arranged and how many electronic components there are in the circuit. All units have the variable speed controlled by a PNP power transistor (this is the fan control which Andrew mentioned) which operates as an emitter follower buffer on the fan speed rheostat. The rheostat has low speed when output is close to the battery volage and higher speeds as the output voltage decreases. At the max fan speed position, another circuit comes into play and switches a relay that shorts out the PNP transistor and gives the fan full voltage and speed - this is the only bit that is working on your car at present. If the power transistor is kaput then any substantial PNP unit from Disk Smith or Jaycar should work - try a 2N2955 type or equivalent.

    The recirculate system works on two flaps controlled by two tiny geared motors which you can see beside each fan motor in the interior air intake plenum. Power is applied to these while the ignition is on and using the recir switch and a relay it is reversed one then the other so that the motors drive the flaps to either extreme. THis is a bit dodgy as the motors often get some water ingress and gum up with the power applied all the time. So check to see if the motors are getting power and if the polarity is reversing when the switch is set to the other position.

    I do have a circuit diagram which should help you. It even has helpful descriations on some of the components.

    I will try to upload a circuit diagram but if this doesn't work, PM me with your email address and I will send you the relevant ones, unfortunately each page is about 1.3Mb.

    Regards,

    Ken Wilson

  5. #5
    1000+ Posts Dave's Avatar
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    Ken W's diagram here


    Ken on Dave's PC


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