Complicated A/C and Blower Motor Problem
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Thread: Complicated A/C and Blower Motor Problem

  1. #1
    crv|oc Rank: Member
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    Complicated A/C and Blower Motor Problem

    HONDA CR-V: 2000
    Alright guys and girls, I've got a pretty strange one for you. This one is giving me a fit and I'm coming to you already armed with a 1,395 page Honda CR-V service manual and plenty of know-how as far as diagnostics go but I'm flat out stumped on this one.

    Symptoms...yea, two of em.
    1) Blower Motor only works on high(I know what you're thinking...)
    2) A/C compressor and fans do not come on...period.

    Start off with 1)Blower Motor Speed deficiency. You're probably thinking power transistor module. Well I am on the 3rd one, swore it was that from the testing and research I've done but after installing the 3rd Honda genuine part I'm now presented with 2 options. It's not the Power transistor module causing the issue, or whatever is causing this problem instantly fries the power transistor module so scratch out replacing the power transistor module because I've done it twice already with brand new Honda parts and that didn't fix it, what are the chances of that? Slim.

    2) A/C compressor and fans do not come one.
    All relays for the entire system check out.
    I've ran the associated tests and really, the two options as possible fixes from the flow charts I followed in the service manual are...apparently the correct fix. That is, to replace the heater control panel AND the PCM. Tricky eh?

    Riddle me this, why would I be getting voltage at the PCM #17 terminal(Blk/Red wire going from PCM to Compressor relay inductor) with A/C turned both on AND off yet the relay is not energized(Nevermind the other side of the inductor that is a Key-on hot blk/yellow wire) You'd think with voltage at both ends of the inductor the relay would be tripped thus turning on the compressor...NOT. The manual says if you ARE getting voltage at this terminal then perhaps the PCM needs to be replaced but for me, that's contradictory. It's basic electricity...if 12V is flowing through an inductor on a relay that is normally open...when that 12V is energizes the inductor it closes the relay switch and thus feeds 12V to the compressor which isn't happening.

    Like I said, I'm friggin lost. I have to say, this system is extremely over-engineered. For crying out loud, basic switches and relays have worked blower speed and AC compressor activation for years. Honda had to goof it up and make it just about impossible to fix by yourself by integrating them into the friggin powertrain control module and a heater control panel that is more complex than an old Packard Bell.

    I was thinkin it's the heater control panel so I replaced that with a used one but that didn't fix it so I put the old one back in. The used one may have the same problem but c'mon...how realistic is that? So far I don't have A/C or a blower motor that works worth a damn and my dash has been gutted for about 6 months working on this in my spare time. WHAT THE F?

    Thank you very much....if anyone wants, perhaps for sparing your knowledge and expertise I could maybe send you the service manual if that would at all benefit you. I try
    Last edited by Aweasel; 07-11-2009 at 09:09 PM. Reason: added year of car

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  3. #2
    crv|oc Rank: Member
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    Oh and I'm pretty much convinced at this point that because of the fact that there are 2 problems there is a discrepancy in testing and troubleshooting procedures...IE the factory service manual flow charts are pretty much useless because I'm getting the run-around.

  4. #3
    crv|oc Rank: Member
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    Well. I just bought a used 99' crv and the high blower works and the guy had his mech ook up a toggle sw to turn on the comp, to save money on an expensive repair. I haven't looked at the system yet. It works but a bit of a pain. Maybe mine was like yours...?

  5. #4
    crv|oc Rank: Member
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    See, I can't see how that would be a good idea because the way I understand it the compressor goes on and off as per the air conditioning pressure switch...builds pressure, stops compressing, comes back on. Surely you've heard an AC clutch engaging and disengage while a car is idling.

    That and both fans must run at all times when A/C is on.

  6. #5
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    Both fans do "not" have to run. So are both fans not working? I added some reading and a self diagnostic test to do. Did you check the Evaporator Temp Sensor? It could be that. The self-diagnostic at the end of this post will determine that.

    Fans
    How the Circuit Works
    Radiator and condenser fan operation is controlled
    by the powertrain or engine control module (PCM or
    ECM) and the radiator fan switch.
    The radiator fan and condenser fan relays are
    supplied battery voltage at all times through fuses
    56 and 57. When the ignition switch is in its ON (ll)
    position, voltage is supplied through fuse 17.
    The powertrain or engine control module (PCM or
    ECM) turns on the condenser fan and radiator fan
    for engine and refrigerant cooling whenever the A/C
    is on.

    Radiator Fan
    Voltage is provided at all times to the radiator fan
    relay contacts through fuse 57.
    Fuse 17 applies voltage to the radiator fan relay coil.
    The relay is grounded by the radiator fan switch when
    engine coolant temperature exceeds 199F (93C).
    The relay can also be grounded by the powertrain or
    engine control module (PCM or ECM).
    Grounding energizes the relay, applying voltage to
    the radiator fan motor through the BLK/RED wire,
    the radiator fan relay contacts, and fuse 57.


    Condenser Fan
    Voltage is provided at all times to the condenser fan
    relay contacts through fuse 56.
    Fuse 17 applies voltage to the condenser fan relay
    coil. The relay is grounded by the engine coolant
    temperature switch when engine coolant temperature
    exceeds 199F (93C). The relay can also be
    grounded by the PCM or ECM.
    Grounding energizes the relay, applying voltage to
    the condenser fan motor through the WHT wire, the
    condenser fan relay contacts, and fuse 56.



    And did you try this? It's the self-diagonstic function

    '98 - 01 models:
    Set the mode control dial to the Vent position, and turn the ignition switch ON (II). Within 6 seconds after turning the ignition
    switch on, press the recirculation control switch the required number of times depending on the recirculation indicator light
    status:
    • If the indicator light is ON, press the recirculation control switch five times.
    • If the indicator light is OFF, press the recirculation control switch six times.
    The recirculation indicator light will come on for 2 seconds, then blink the Diagnostic Trouble Code (DTC) to indicate a faulty
    component. If no DTC's are found, the indicator light will not blink after the initial 2 seconds light.


    1 Blink- Air mix control motor. Possible open or short,obstructed door or faulty motor.
    2 Blinks-Blower Motor. Possible open or short or faulty motor.
    3 Blinks-Evaporator temp. sensor. Possible open or short or faulty sensor.
    Last edited by tkcr; 07-12-2009 at 08:49 AM.

  7. #6
    crv|oc Rank: Sophomore
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    Quote Originally Posted by Aweasel View Post

    Riddle me this, why would I be getting voltage at the PCM #17 terminal(Blk/Red wire going from PCM to Compressor relay inductor) with A/C turned both on AND off yet the relay is not energized(Nevermind the other side of the inductor that is a Key-on hot blk/yellow wire)
    The PCM grounds the circuit at terminal 17 to provide a path for current flow. The fact that you are measuring source voltage at terminal 17 simply indicates two facts:

    1) the circuit is NOT flowing current because the circuit is open

    2) the circuit is NOT open between the fuse and the point where you are measuring - terminal 17 at the PCM connector.

    Quote Originally Posted by Aweasel View Post
    You'd think with voltage at both ends of the inductor the relay would be tripped thus turning on the compressor...NOT.
    Your understanding of the premise for electron flow in a D/C circuit is incorrect. There must be a difference in voltage potential within a complete circuit in order for current to flow and do work.

    Quote Originally Posted by Aweasel View Post
    The manual says if you ARE getting voltage at this terminal then perhaps the PCM needs to be replaced but for me, that's contradictory. It's basic electricity...if 12V is flowing through an inductor on a relay that is normally open...when that 12V is energizes the inductor it closes the relay switch and thus feeds 12V to the compressor which isn't happening.
    Voltage does not "flow" - voltage is the term used to describe electrical potential (pressure). Your test results will be very confusing to you if you don't understand that current (electron flow) is what performs work in an electrical circuit. An electrical circuit must be a completed circuit so that current can flow. If a circuit is flowing current, you will not be measuring source voltage drop.

    Now, the A/C compressor circuit will not operate if there is a fault in the blower motor circuit, so I'd advise you to step back and focus on correcting the blower motor issue rather than assuming that there is a fault with the compressor control circuit.

    The blower motor power transistor is an NPN transistor, so the heater control panel will provide a variable positive voltage potential to the base of the transistor to bias the transistor and control operation of blower speeds at less than the high speed.

    You indicate that you have fried several power transistors. Solid state electrical components get damaged when too much current flow is induced, or if the current is avalanced backwards through the circuit. Transistors cannot limit the amount of current flowing through the base circuit - the current limitation is provided by resistance in the base control circuit.

    If I were you, I'd be focused on the circuits between the blower motor, power transistor and control panel, making sure that none of the circuits are open, shorted to ground or shorted to voltage.
    Success is 99% failure
    -Soichiro Honda

    Success is the ability to go from one failure to another with no loss of enthusiasm.
    -Winston Churchill

    Motorcycle Riding in West Virginia

  8. #7
    crv|oc Rank: Member
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    couldn't find any loose/exposed/damaged wires or connectors in the entire circuit. nothing that I can find is shorting to ground or voltage and all wires are intact.

    you mentioned varying voltage at the power transistor. what I did this afternoon is measured voltage at the green/blk wire at the power transistor. According to my manual this is the power transistor base wire and is an output from the control panel. Well according to my meter I'm not getting a varying voltage here which indicates to me the control panel is faulty.

    Ya think if I took it to Honda they would plug in a new control panel to confirm this? No way I'm paying the 600+ for their new control panel but for diagnostic purposes maybe?

  9. #8
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    Did you try the self diagnostic test?

    And it could be a faulty control panel. If the dealership has a test on hand to use, they could try that.

  10. #9
    crv|oc Rank: Sophomore
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    What voltage are you reading at the base control? Does the voltage change correspondingly to changes in the position of the blower switch? Keep in mind that a power transistor will increase current flow from the emitter when the base current is increased.

    The answer to your question of "will a dealership plug in a new control panel for diagnosis purposes" would, in almost every circumstance, be 'NO'.

    It is very unlikely that a Dealership Parts Department would have a control panel sitting on a shelf unless it was a common enough occurance to warrant having such a part on hand. Most parts departments will probably have power transistors in stock as failure of the transistors is not uncommon. Control panel failures are not common at all, and as you have seen from the service manual, there is no "real" test procedure indicated other than making sure the wires are not open or shorted and then trying a "known good" component to see if the problem can be corrected. "Known good" either means taking a component out of another vehicle that is known to be working normally, or taking a brand new (and hopefully 'good') part and installing it. The parts manager isn't likely to agree to purchase the part for you and "eat it" if your vehicle doesn't need it, neither will a service technician or a service manager.

    I am not trying to insult you, and really wish I could help you to diagnose your problem, but your posts indicate an incomplete understanding of the operation of DC electrical circuits. This would make a diagnosis over the internet very frustrating and be a hit-or-miss proposition. You may be better off taking your vehicle to an experienced Honda technician.

    One of the most important observations that was ever made to me by an electrical instructor (whom I had a great deal of respect for) was "Sometimes what you think you see, you don't really see at all". This statement has always meant to me that it is very important to KNOW what you are testing for and KNOW what your results indicate. The first time in an electrical diagnosis that your thought changes from "this is interesting" to "this doesn't make any sense" you are in trouble.
    Success is 99% failure
    -Soichiro Honda

    Success is the ability to go from one failure to another with no loss of enthusiasm.
    -Winston Churchill

    Motorcycle Riding in West Virginia

  11. #10
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    There are a few heater control units on E-bay. I'd try one of those before I'd take it to the dealership. By the time they fiqure it out, you'll have a few hundred in diagnostic troubleshooting.

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