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Air Conditioning Fail

Discussion in 'General Tech and Maintenance' started by reckedracing, Jul 17, 2012.

  1. reckedracing

    reckedracing TTIWWOP VIP

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    2004 civic ex
    a/c compressor not kicking on, already ruled out (low?) pressure switch by the dryer canister
    believed to be electrical fault
    low side reads 120ish psi which is normal for an equalized non functioning system
    i know its extremely high for the low side if the system worked, but thats not the case

    so any ideas on where to start looking for the electrical fault?
    i tried relays and fuses but did not find one specifically for a/c and i swapped every relay that could possibly be associated with the a/c under the hood.
     
  2. Briansol

    Briansol Admins Admin VIP

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    could it be the switch? do other items like heat/defrost/etc work?
     
  3. reckedracing

    reckedracing TTIWWOP VIP

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    everything else works, but the a/c does not come on with defrost
    if my arm wasn't fucked i would have fed the compressor hot already from a toggle just to shut her up, fml
     
  4. dc4dude

    dc4dude Member

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    compressor clutch working? see if its getting power? put power to it? compressor spin freely?
     
  5. reckedracing

    reckedracing TTIWWOP VIP

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    yea, that would be my normal diagnostic procedure but i have to wait till i get full use of my arm back to get down in there.
     
  6. civicious

    civicious FüK-VTEC VIP

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    1. Locate the A/C pressure switch on the high side A/C line by the alternator. The wire colors are Red (RED) and Blue (BLU). With the pressure switch unplugged, the RED wire should have 10 to 12 volts reference voltage on a voltmeter. When the reference voltage is grounded, the Multiplex Control Unit (MCU) will see an A/C request and send that request to the Engine Control Module (ECM).

    2. If there is no voltage to the A/C pressure switch, unplug the A/C Compressor 3-terminal connector, check the Blue/White (BLU/WHT) wire on the harness side of the connector, and look for voltage. If there is voltage, then backprobe the BLU/WHT wire, plug in the connector and start the vehicle. Then ground the BLU/WHT wire and verify that the A/C compressor and condenser fan operate.

    3. Test the A/C Thermal Protector. The voltage on the BLU/WHT wire should go through the A/C Thermal Protector and then to the A/C Pressure switch RED wire. Check to see if the A/C Thermal Protector is open or if there is a wire harness problem between the A/C thermo protector and the pressure switch.

    4. Always verify that there are no codes in the climate control system. If there is a problem, the climate control may not ground the A/C request circuit.

    It's relatively common for the heater control panel to not ground the Blue wire. The A/C Compressor Thermal Protector is also a commonly failing part.

    Also, NEVER jump voltage to the A/C request circuit when testing out the A/C system. This isn't a 1990 Civic, there's a lot more involved than just a relay sending 12v to the compressor. Putting power to random wires in the circuit is a good way to fry the control unit.
     
    Last edited: Jul 18, 2012
    1 person likes this.
  7. reckedracing

    reckedracing TTIWWOP VIP

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    :worthy:
    where did you find this info? or did you just write it up?
    and thanks for the tip on not supplying voltage, didn't really consider the control unit

    1. low pressure switch was verified by jumping it out, i was told this was a simple open or closed switch, would i do any damage by just jumping it?

    2. location of a/c thermal protector?

    3. how do you check climate control system for codes?

    4. the heater control panel is a failing part or something leads it to not ground the blue wire?
     
    Last edited: Jul 18, 2012
  8. civicious

    civicious FüK-VTEC VIP

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    It's what I do for a living, from time to time I like to actually contribute something 'useful', heh.
     
  9. dc4dude

    dc4dude Member

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    What happened to your arm???
     
  10. E_SolSi

    E_SolSi Member of the 20 nut club Moderator VIP

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  11. civicious

    civicious FüK-VTEC VIP

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    1. Jumping the pressure switch should be fine. You still need to make sure there's voltage present there though - the switch could be good but the line could have an open, and jumping it wouldn't tell you that.

    2.
    [​IMG]

    3. Using a scan tool, such as a Snap-On Solus, OTC Genisys, or an OEM Honda HDS.

    4. The heater control panel is the central control unit that controls all the A/C and climate control function - the 'climate controller' if you will. Simply put, it's the thing with the buttons that you use to turn on the A/C and adjust the temperature. An internal fault could cause it to not ground the blue wire, among other things.
     
  12. reckedracing

    reckedracing TTIWWOP VIP

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    should i look into having it scanned at honda as a first step?
    or check the electrical out first before getting a real scanner involved?
    i currently only have the obd2 scanner/code clearer

    and would there be other trouble signs for the heater control assembly?
    if all lights function and everything else works for example
     
  13. civicious

    civicious FüK-VTEC VIP

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    If you have access to the hardware, the first step should always be running a full system scan. It takes ten minutes, and can pinpoint the problem in most cases. For anything manufactured after 2000ish, OBD2 scanners are practically worthless for anything other than engine-related fault codes (and sometimes, they're even worthless for that). You can also actuate the a/c compressor with a full scanner, and that'll allow you to see whether or not the compressor is even being commanded on by the control unit. However, if you DON'T have easy access to a scanner, it's a good idea to go ahead and proceed with the pinpoint tests - those are free.

    There wouldn't necessarily be any 'other' trouble signs - simply failing to command one circuit on could be the only problem with it. E46 BMW's have that issue - the control unit won't command the compressor on. Everything else works fine - blend doors, fans, blowers...the compressor just isn't commanded on. Repair CAN be done at the component level, but in most cases the cost of replacing the unit versus the cost of labor for a component-level repair is equal if not less.

    Make friends with someone at Honda and get them to scan it - either way it wouldn't hurt to go ahead and do all the pinpoint tests that I've posted earlier. It could be something as simple as the thermal protector, and that's something that should only take a few seconds to check. An alternate way, other than checking voltage thru it like I posted earlier, would be to disconnect both connectors and measure resistance thru the thermal protector - if it's open, it's bad.
     
  14. reckedracing

    reckedracing TTIWWOP VIP

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    thanks for your help Wil, i'll have to check it out this weekend and see what i can accomplish in limp mode (a reference to my arm...)
     
  15. Jeef

    Jeef NO MA'AM Moderator VIP

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    We should sticky this.
     
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