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Heater Control Panel - Another FIX

Discussion in 'Electronics' started by Rick89GTS, Nov 27, 2009.

  1. Rick89GTS

    Rick89GTS Well-Known Member Moderator Donated!

    Cross-reference to the main, archived 'How-To' HEATER FIX thread:

    Cliff Notes:
    Except for the AC button, ST165 AC and non-AC heater control panels are the exactly the same :mrgreen:

    My HVAC panel with AC crapped out again and nothing was available at the junkyards. I had a spare HVAC panel without AC but I got to thinking; to speed production Toyota probably made the same circuit board with just a block-out button for non-AC cars, right? So I took apart both an AC panel and a non-AC panel and guess what? The internals are both the same.

    You can simply remove the block-out button and swap in your AC button and you'll be good to go. (I had disassembled everything so I swapped the circuit board into my panel with the AC button.)

    So this broadens your options if you can only find the non-AC panel and your car has AC.

    CAUTION: be extremely careful if you're removing the second circuit board. It is attached to the LED's with 2 delicate plastic prongs on each side of the LED's - they break easily.

    Below: the non-AC heater control panel vs AC panel.

    Below: comparison between the block-out button and AC button. Those four legs prevent the block-out button from going down.

    Below: use extreme caution if removing this circuit board from the shell casing!

    Below: this is the disassembled 'non-AC' panel. Lo and behold, underneath the black block-out button, you can see it does indeed have the AC switch. Also a good view of the fragile LED prongs and internals.

    Below: another view of the internals

    Below: test run to see if the AC button will work....
    Below: the AC works!

    Edit: the info below refers to the LHD 88-89 HVAC panel only - the 86-87 ones are different and I have not diassembled that one yet.
    This last pic is something that's been plaguing us 4th Gen'ers for a long time.
    I believe I've finally identified which leads go to the heat slider bar - they are the No. 1 and No. 10 Pins. If you resolder all the red circled points, it should fix your heat. If you try it and it works for you, post feedback :)

    Last edited: Jan 3, 2013
  2. Stig

    Stig ST162 Guru Donated!

    Anyway I've been having hassles with the heater unit (1989 model) in the TEMS, flaps not opening,
    fan not working properly, lights not working, temp not changing etc - very frustrating banghead

    I decided to repair it and I can report that replacing it with the 1987 version does not work,
    the wiring is different.
    So I re-soldered each and every joint carefully and VOILA!, the damm thing is working properly now.
    The 4 tiny 12V bulbs had all failed and after getting a price of $17 each,
    I decided to try something different.
    I had some spare blue 12V T10 LED bulbs, so I opened them carefully and removed the LED's
    complete with the resistors to go with the new blue interior theme

    Carefull as the resistors tend to break right at the ceramic - rendering them uzeless

    I soldered them into the circut board as trying to get them into those tiny silly holders proved futile

    Carefull as the LED's will only work in one direction, this is the correct positioning for the LED's

    I'm happy to report that the LED's are waay brighter than stock, cheaper and should last longer,
    you can change colours easily and re-soldering the joints definitely does work!

    Hovever when I re-assembled it the LEDS don't give an even light, so soldering in some of the bigger bulbs (without the holders)
    may be a better option
  3. Stig

    Stig ST162 Guru Donated!

    Take out the blower resistor and inspect, I suspect you have some coils missing

    Agreed, replacing the heater valve is easy, the cable is another story, but I've yet
    to see one seize up. Most likely the drag from the motor you're feeling

    For more tips on how to clean out the system and repair dash vents etc, try my thread
  4. ST165-2765

    ST165-2765 Well-Known Member Donated!

    I have done alot of investigating into the heater control panel and have found 2 main issues
    1) temperature slider does not change the heat setting
    2) individual buttons no longer iluminate or function

    Temperature slider
    Rick has identified the correct points on the main circuit board where the temperature slider
    connects. Unfortunately Toyota has used the contact points for the slider as the means of
    attaching the slider to the board instead of permanently attaching the slider to the board. I
    do believe that since the slider knob sticks out the front of the control panel over time the
    slider knob has been hit and forced into the control panel putting stress on the solder points
    for the slider and eventually breaking them free from the pcb. I think the same is true for the
    malfunctioning buttons to, their getting hit to hard and are pressing on the leds eventually
    breaking them free from the pcb board. Another poor design, the led should be in parallel with
    the button not in series but thats the way it goes

    Heres some close ups of the 3 solder points, you can easilly see where they have broken as
    compared to the other solder joints in the pictures. These are the only points you should need
    to re solder, I know Rick has also identified points on the flexible cable and points on the smaller
    pcb where the plugs connect but I do not believe they are broken


    Individual buttons
    I have also found that individual buttons can fail and in each case where the button has failed
    I have found that the led for the button has become detached from the PCB and does not
    iluminate anymore

    Repairs (88-89 control panel)
    if you have buttons that don't work check the coresponding led and re solder it (yellow circles)
    if the temp slider doesn't work re solder the conections inside the red circles
  5. 89GT-S_Coupe

    89GT-S_Coupe Active Member

    Finally tackled this issue today!!! My HVAC now works perfect!!! :cool:
  6. Rick89GTS

    Rick89GTS Well-Known Member Moderator Donated!

    Hey Dave, I haven't visited this thread for a while, so nice to see your further investigation into this issue.
    I will give this a try as well; it seems logical to me.
    Anything we can do to solve this problem is a bonus to the community.
    I cross-referenced this post to the archived thread as well.
    Good work, thanks, Rick

    Hey 89GT-S_Coupe, have any pics of your 510 to share with us? I love those cars; had about 6 of 'em in my youth, LOL
    Last edited: Jan 3, 2013
  7. 89GT-S_Coupe

    89GT-S_Coupe Active Member

    Sorry for the delay.... Haven't been on the forum in a while...

    I do have some pics! These are just a few I could find off hand..

    WP_000354.jpg WP_000037.jpg WP_000355.jpg WP_000356.jpg WP_000357.jpg WP_000358.jpg 422213_3962084303371_1997194166_n.jpg 580920_3962084783383_240278661_n.jpg 559253_3962084063365_677271533_n.jpg 556553_3936087453466_2084374423_n.jpg
  8. cjdoolan

    cjdoolan Guest

    Second circuit board

    Have removed control panel and am trying to pry loose second board to access lights. Is there only the side clips that seat board to body? Doesnt want to come and am worried about breaking something. Any clues appreciated. Chris
  9. Matt Mathews

    Matt Mathews Guest

    Heater Control Panel available

    Last winter the heater in my '88 GT didn't work, except occasionally. I was able to find another one and had it gone through by an HP friend recently. It now is back, and is available for anyone here. I guarantee that the heater circuits are now fully functional. My AC has other issues, and still doesn't work. I have been told that it is a problem with the AC anplifier. I don't know what to do about that. Anyway, the heater circuit board is now functional, and I am open to an offer from someone here who wants a good one. You can e-mail me direct at mattm204@gmail.com if you want to discuss it.

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