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Thread: AC & Heater Control Problem 91 K1500 Silver

  1. #1
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    AC & Heater Control Problem 91 K1500 Silver

    I have a 91 Silverado k1500. It has the push button AC and heater control panel. The panel does not function - no fan - no heat - no air - no lights in the panel. The part number label is no longer on the panel but it is the style with the "RECIR" button rather than the "MAX" button (part # 16204785).


    I installed a used 16204785 (max button style) and found the same results. No function - no lights in the panel. I am told the replacement panel was tested aand worked.

    There is current showing at some of the connector points on the truck side connector plug.

    I have cleaned the connector points on the back of the panel and in the plug connection.

    I have checked the fusable links near the fire wall and all seem fine.

    I have checked the fuses under the dash and all are fine.

    There are three relays behind the glove box. I think one or more have something to do with the AC. I have heard buzzing from these relays in the past but this has gone away. The panel did not work at all before or after the buzzing problem.

    Any suggestions?

    Thank you
    JBB

  2. #2
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    Welcome to the forum JBB.

    I think you have a open connection for ground. You say you don't see or hear anything
    before or after head swap, but you do have "currents". All share same ground.
    The buzzing noise you heard may be the effect of relays cyling as they lose
    good ground connection. Believe the relays you are taking about are L/M/H for blower.

    by "currents" I'm guessing you meant votage. As I recall, you should find
    one wire hot at all times, one more with key "on" and a third with park lites on.

    Couple odd items on 91, that's the year they introduced the lo-refrig-detect
    system. If set off by short on-cycle times it will lock head and flash lights.
    It will repeat that every key on for 2 minutes. Doesn't seem your problem.
    Another thing on the 90-93s was a sensitivity in the heads to poor Ign signal
    at first contact. Can be caused when making battery connection or Ign Sw.
    Sometimes just cycling switch would reset and GM didn't take that as too serious.
    An old note of mine suggests the part number for more stable head was #16152129

    I recommend verifying the ground and if that gets the head working,
    you may need to replace blower relays if the chattering connection
    cooked them inside. Head should work without relays good I think,
    so one step at a time.

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    Thank you Mr. Crabtruck.

    I am hoping this problem is as simple as a ground problem. Where might I look to correct a ground problem?

    There are several connection posts under the hood on the firewall behind a plastic cover toward the passenger side. I have cleaned all of these connections.

    I will check the connections again for current/voltage. It's been a while since I checked this but I seem to recall it registering on the voltmeter at 2 or 3 points. I probably tried this with the keey on and with the key off but I'm sure it did not try with the headlight/parking light switch in the on position.

    JBB

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    Don't put "Mr" in front - spoils whole effect

    I'd start by blower end of grounds since the problem doesn't seem
    to be showing up in other systems. Find the grounds coming from head
    and joining with blower and follow that down.
    Believe it even goes through a plug-in in addition to it's splices.

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    Still having heat/ac problems

    I have finally had some time to work on my problem but I have made no progress. I simply have no heat or ac. No lights or function at the electronic control panel. No functioning of the AC, no blower - nothing.

    I have gone through the wiring from the control panel plug back toward the passenger side to the blower box and fire wall and did not see any problems. I unwrapped the bundled wires and all looked good.

    There are three relays behind the glove box. There is power on various wires goinging into the resistors. I have swapped the connections between all three with no change. Is it possible that one or more bad relays would create a situation like I have?

    I pulled the resistor out - looks fine - zero ohms when checked on either side of the resistor.. There is no power at all going into the resistor - key on, key off, lights on, lights off.

    There is a splice in the wiring harness with 2 browns, 1 gray and 1 black going toward the drivers side. These 4 wires lead into a plug connection that is white and gray. I separated this plug and found one prong on the drivres side showing power. I presume these 4 wires go off to the ignition switch and light switch. Should more that one of these have current with the ignition on or off or with the lights on or off?

    I am thinking about taking this to the shop but I can only imagine many hours of diagnostic time ticking away at $60 per hour.

    Any and all help will be greatly appreciated.

    JBB

  6. #6
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    There are several connection posts under the hood
    on the firewall behind a plastic cover toward the passenger side
    Just FYI: that's the "battery junction block" and it's like the starting point
    of all the trucks hot wiring (no grounds) except the starter and altenator.
    Usually there is a wire from battery with a fusible link as the "in" and then
    other fusible link wires go from there as "outs". Like a giant wire nut.

    In defense of taking it to a shop, if that's what you need do do,
    I would point out that they have experience and toys you do not have,
    so they would be able to diagnose this in short order and that is
    something you can call and ask them about as opposed to repair time.

    Now if you still are going after this yourself, I'm guessing this is a typo:
    "There is power on various wires goinging into the resistors" (RELAYS??)
    .


    .
    This would be good because each of the relays should gave a hot from
    the same place with the key on: the heater fuse.
    Check out this drawing I did - should be similar to yours.
    .
    Attached Images Attached Images   

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    Crabtruck (gotta be a story behind this name)
    Yes, the picture and diagram look similar to what I am dealing with. The 94 seems to have 4 relays whereas I have only 3. Thank you for posting this information. Chiltons and Haines leave much to the imagination. I'm a pretty smart guy but I do not do well with wiring. I can read a wiring diagram only slightly better than Ray Charles can read Chinese. I have power on both sides of the heater fuse. If I recall correctly, I have puwer on the brown wires going into the relays (yes - typo when i said resistors). I have no power on the tan lines going to the blower door motors. I have no power on the purple between the resistor and the blower motor. There is a black wire going to the blower motor area below the computer near the purple wire - i did not check this one. Do you think it is possible that the wiring from the ignition and or light switch could be the root cause of all? Thinking that the ignition must be on to get any function at the electronic control panel. If the control panel is not broken then it might be prevented from performing any function without the proper signal or power coming from the ignition switch. Sound logical? or does it sound like I'm grabbing for straw here? I do have a good shop - Ron's auto in Webster NY. Great people but the truck was free to me and I am trying to keep it as close to that as possible.

  8. #8
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    Quote Originally Posted by jbbarry View Post
    Crabtruck (gotta be a story behind this name)

    ...The 94 seems to have 4 relays whereas I have only 3.
    Fourth is A/C, maybe underhood in 91 IDK
    .... I have power on both sides of the heater fuse.
    If I recall correctly, I have puwer on the brown wires going into the relays
    Heater fuse and key = ok
    .. I have no power on the tan lines going to the blower door motors.
    5v wires only with working head, (position sensors, not doors)
    ...I have no power on the purple between the resistor and the blower motor.
    With Controller off or not working, one is and one isn't.
    There is a black wire going to the blower motor area below the computer near the purple wire
    Most blacks there should ohm to ground (check for voltage first).
    possible that the wiring from the ign and or light sw could be the root cause? NO
    ignition must be on to get any function at the electronic control panel. Yes.
    Stack of relays in drawing are lo.med,hi,AC not order in truck (med,AC,lo,hi)

    You do actually have AC right ? compressor, accumulator, all that stuff??

    First check 2 grounds at head are good, otherwise nothing counts.
    Not to be confused with 2 door sensor grounds on head. All are black.

    Next with no key, park lights on, check one brown wire has hot.
    That's not needed but shows doing meter right, and ID's wire.
    Should be able to get with either of 2 grounds above.

    With key off, head in or out, should have batt at head, Lo relay and little resistor.
    That's relays unplugged, if connected at least two relays would
    have 2 hots and little resistor would be hot on both sides.
    Are you seeing a 3-wire resistor and a 2-wire one next to it ?
    A picture would be so cool right about now.

    Key at on, lights off, head in or out, should have batt at head, all relays (AC is 2 points)
    Relays in or out = same.

    For fun and info, head out, no key, unplug low relay and jump Red to Yellow
    with a 15A fused wire. Does blower work ?

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    wow - thank you for the interest. I'll have more details and pic's on Saturday. What color are the groud wires at the head? I would generally think black?

    Yes, I have AC - all factory installed.

    It's a great old truck. Not pretty but it is a 91 with only 80k miles - never towed - never plowed. My 13 year old daughter is pretty much claiming it to be hers. Not sure I'm going to want to give it up when she learns to drive.

  10. #10
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    Are you using a black and white monitor ?
    The grounds were black in my drawing.

    Come to think about it though, you may want to print
    and take it with you in the truck, so you can note
    what's same and what's not - too much to just remember.

    .

    Let the 13yo drive it -
    it's tough, cheap, and simple to fix & drive.
    (She gave me $5 to say that)
    Last edited by crabtruck; 10-22-2009 at 12:13 AM.

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