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Thread: 2003 GM LSE HI/LOW AC Pressure diagnostic

  1. #1

    Default 2003 GM LSE HI/LOW AC Pressure diagnostic

    Hey, got a 2003 GM LSE with 212k miles! About 3 weeks ago i noticed the A/C would seem to fade out, then the fan wouldnt blow at all. I pulled the EATC resistor and re soldered the problematic pins on the board. The fan began to work like a charm!

    Now its taking about 5 min on average for the AC to kick on.

    With the car running and the pump off im seeing 90psi on the low side and 90psi on the high. So the system is static.

    When the compressor kicks on im getting the low side slowly fluctuating from 35psi to 45psi to 35psi in that continual loop. The high side on the other hand is rapidly bouncing between 200 and approx. 215psi.

    After a few minutes of running the low side appears to level out at 40psi, but the high side is still bouncing.

    The car will cool, but dosent seem as good as it once was. Im sure with its age it needs a new evaporator, orifice tube, recharge, etc. However im not sure what the fluctuating high side means, just want to make sure i dont have a compressor problem first.

    Thanks for any help!

  2. #2

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    Is the compressor making any noise? It would seem like there is a leak in the high side somewhere. Id suggest looking for any pag oil around the lines/compressor/etc and running some uv dye through the system if you cant find a leak visually.


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  3. #3

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    The compressor sounds great, quiet as can be. Iím not seeing any leaks but I will check it out this evening.


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  4. #4
    Beater gonna beat sly's Avatar
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    what was the ambient temp outside when you got those pressure readings? If it was around 70-75F, that all sounds about right. If it was in the 80s or 90s, the high side is low which could mean the compressor is on its way out or the orifice tube has blown through and isn't restricting the flow enough.

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  5. #5

    Default 2003 GM LSE HI/LOW AC Pressure diagnostic

    Yea sorry it was about 75, later in the day and in the shade.

    And it may be doing exactly what it needs too. I just donít want to go through all the work to have mid diagnosed a bad compressor.

    Could the late compressor activation be a bad switch? Something telling the system not to engage until maybe the from the engine causes the ac system so swell activating the pressure switch to run the pump?

    I just re did my Ď03 excursions ac system and it kicks in right at start up. So cold itís painful...

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    Last edited by taylorendicott; 06-04-2019 at 05:38 PM.

  6. #6
    Beater gonna beat sly's Avatar
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    The excursion probably has an expansion valve system as well. Those tend to be more effective than the orifice valve system in the panthers. The excursion probably also has a heater shut-off valve for the front system similar to what my expedition has (which I disabled because I want temperature control under MAX settings and without heat, you just can't control the temps). The panthers don't have a shut-off for the heat so there will always be a little leakage of heat from the heater core into the ducts and the evap has to cool down and overcome that heat as well. If the compressor kicks when you switch the system on, you should get "cool" air in about 10-15 seconds. Cold air may take anywhere from 3-20 minutes depending on just how freakishly hot it was in the car at startup.

    Take my 93 for example. It'll start to freeze you out after 30 minutes even in 105F heat... but it takes the full 30 minutes to do that. Typical 95-100F summer days I'm comfortable after about 10 minutes. But my comfort level is around 80F. And I'd say this is the best this system has worked since it originally had R12 in it. (It's R134a now.)

    My 03 expedition on the other hand will freeze you out in about 15 minutes on those same hot days, but it has dual (front and rear) HVAC and uses expansion valves.

    Only two things are infinite, the universe and human stupidity, and I'm not sure about the former. -- Albert Einstein
    rides: 88 MGM (SOLD), 93 Vic, 2000 Crown Vic, 2003 Expedition
    Quote Originally Posted by gadget73
    ... and it should all work like magic and unicorns and stuff.
    Quote Originally Posted by dmccaig
    Overhead, some poor bastards are flying in airplanes.

  7. #7

    Default 2003 GM LSE HI/LOW AC Pressure diagnostic

    Yea the excursion runs with an office tube in the front and a TXV on the rear ac.

    The merq on the other hand, the compressor itself wonít kick on until about 5 min of running. Thatís my real concern. Iím not sure what is causing the delay in the activation of the compressor.

    I think the merq also has a heater shutoff, but I cant confirm that without leaving work to go look. Hell might be an excuse to leave.


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  8. #8
    I'm an air-conditioned gypsy gadget73's Avatar
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    That shouldn't be. Normally the compressor engages within a few seconds of startup. Might be worth poking a voltmeter in at the low pressure switch to see if its getting power right after startup. No power there is likely some gremlin inside the EATC unit. I know some of them had an issue with a relay inside that needs to be re-soldered to fix a no compressor engagement problem. If you have power there, see if you've got power at the compressor itself, or at the WOT relay since thats a little more accessible. If you have power output at the WOT relay, the pressure switches are both OK, the EATC unit is OK, and the PCM is not commanding the compressor to not run. At that point its probably a clutch shim issue. Whacking the front of the clutch to see if it grabs would be the test there, but be extremely careful poking things in around the belt system with the engine running for what I hope are obvious reasons. Too much of an air gap on the clutch can cause it to not pull in reliably.

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  9. #9
    Beater gonna beat sly's Avatar
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    Yeah... probably the EATC head issue. I've never seen a working system that took minutes to kick the compressor for the first time.

    Only two things are infinite, the universe and human stupidity, and I'm not sure about the former. -- Albert Einstein
    rides: 88 MGM (SOLD), 93 Vic, 2000 Crown Vic, 2003 Expedition
    Quote Originally Posted by gadget73
    ... and it should all work like magic and unicorns and stuff.
    Quote Originally Posted by dmccaig
    Overhead, some poor bastards are flying in airplanes.

  10. #10

    Default 2003 GM LSE HI/LOW AC Pressure diagnostic

    Yea it happens every time I turn it off and back on.

    Iíll take a look tonight and let you know why I find.

    Thanks for taking the time

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  11. #11

    Default 2003 GM LSE HI/LOW AC Pressure diagnostic

    So I found a little article online about a guy who noticed if he would push down on the AC fuse relay the compressor would kick on. So I went out and swapped the ac relay with the horn relay. Started the car and the compressor kicked right on.

    We will see if this actually fixed it tomorrow when itís in the 90ís.



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