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Testing Subaru Pressure Switch

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  • #31
    Messed up as this is Gnarsinski's thread and great just quoted "huntingdog" mixing myself up.
    Refresh - Pressures now good enough it should have tried on it's own but didn't so was jumped.

    Quote from post #14 by Gnarsinski ">If I apply 12v to terminal 2, both fans come on and the compressor engages. So maybe my issue lies with why I'm only getting 5v into the switch?<"

    There's the oops! There isn't 12v for the computer controlled switch it works on the 5v then sends probably grounds to engage clutch with batter power while running more than 12v or should be.

    Quote part of post #17 by Huntindog ">Both the high and low pressures are too low. Looks to be under charged. A leak some where is a virtual certainty. Under charged and the compressor protections are keeping it from running, and doing damage. Don't jumper it any more.
    Find and fix the leak, and put a proper charge in it....<"

    Note what he said DON'T JUMPER IT ANYMORE. Also said exactly correct that you must begin with proper charge. I'll add to the ounce! That has to be listed under the hood as it could differ from any published chart.

    Summary. Nacho has sent diagrams I don't own software for specific vehicles - sorry. If in the course of forcing compressor to work even if low with 12v to a wire back to computer controls you just may have blow the thing.

    It now matters just how this was jumped with improper voltage why we can't proceed well with out knowing if the PCM for this is working or not never mind the switch which is the subject line.

    No jumping like very old days prior to HPCO (high pressure cut outs) were mandatory for 134a vehicles. Can't thing of them used before that. That is responsible for lots more than just over limit pressure sensing and likely controls high and low fans for condenser speed or if fans are needed at all and aren't if either plain cold to begin with or at vehicle speed with enough air flow.

    Need to know how this was jumped which is always a no-no and now suspect the PCM is blown for more diagnosing. Unfortunately to diagnose that we need to rule every other possible thing out then blame it. Most wouldn't work just new rather programmed for this exact car model or worse exact can by VIN only a dealer will be able to do but doubt this car. It's never happened to me blowing a PCM so at least need to know if it's in the cards,

    MetroWest, Boston


    • #32
      Since the OP has the diagrams from Ignacio, and according to him term 1 is supposed to get 12 volt feed from the battery buss, I am not convinced that this half of the switch is 5 volt. The ECM and ground (terminal 3 &4) may be low voltage. It is easy with a digital meter to register stray back feeds, it will show voltage but disappear when any load is applied. Digital meters don't "load" the circuit the way analog or test lights do.
      1st and foremost the person needs to understand how the system is wired and the function of each switch. From the description, it sounds like terminal 1 supplies the power from the battery buss,, goes thru the LPCO and possibly HPCO then out thru terminal 2 thru the frost switch and on to the compressor relay, At least that's how I read his post. If that is the case, it sounds like all controls are 12 volt (terminals 1&2). Terminal 3&4 likely give a ground signal to the ECM when there is operating pressure in the high side, to boost the idle speed a bit, it also could be a variable resistance to tell the ECM the compressor load, but I doubt it.
      I have to go off how the OP'er described the circuit, if his description is off, all bets are off.


      • #33
        We need some info from OP on what was done not just tested. So true, use only DVOMs to observe and now LED test lights highly unlikely to draw current themselves to cause a problem. Plain jumping things to me is suggesting you just bump the wrong wire with 12V to something 5V then we get lost.

        HPCOs are loaded with info not just to shut a system down so refrigerant doesn't blow up or trip a mechanical blow out valve. PCM takes all factors in, load of A/C on is noticed so ready to hold idle speed so load isn't causing a problem. It takes that info in with throttle position, speed, air speed of incoming air and it's temp, manifold actual temp, which gear the vehicle is in and no doubt if it thinks engine is too hot. With that all adjustments made.

        That thing if jumped or empowered backwards by any mistake all bets off.

        They cause enough trouble with just dealing with wiring harnesses rubbing, being wet in the wrong places or from recent work something bumped and not noticed.

        Lost without some more clues.

        May have missed it with this now on page 3 but why was anything about this A/C touched at all and was known amount of refrigerant reinstalled or some guess. We just don't really know unless clearly told.

        Need more info not just how to test a HPCO unlikely alone any problem just being thought about and was the initial question. Not sure and would be it's own test of what it does to change via what voltage by temp no doubt back to PCM. If outside of limits for PCM it may not fail in a predictable probably default to some limp mode leaving anything A/C out of it so the car runs at all????

        MetroWest, Boston


        • #34
          They way I read it is no A/C work was done prior to this problem. He didn't even have gauges when he started. Bought gauges and had static pressure that equates to 77 degs. When he jumped the compressor it jumped to 120 psi (94 deg f) high side and 20 PSI low. We don't know how long the compressor was jumped and if the pressures changed any with running.


          • #35
            My server was totally down for 8 hours - nobody's fault couldn't see this.

            Good observations Cornbinder89. No equipment to begin with, pressure when acquired are NOT enough to "condense" a vapor to a liquid to evaporate at 77F so essentially none of this makes sense.

            Jumping things for testing just isn't a way - done with those things you just miss for a spark to the wrong terminal and can blow $2,000 bucks just like that and lucky if only don't have A/C.

            About now there's so little known that totally matters and refrigerant messed with unknown if it even was OK before can't know where to proceed without knowing exact charge is in it, then you can diagnose why it doesn't work starting with finding the most likely a leak that could be so fast you might even hear it. If not before even running engine check for leaks and none of this seems to have been done.

            Can't advise more than send it out for diagnosis and then decide if OP wants to take this on at all or not,

            MetroWest, Boston


            • #36
              Might be a little late now, but having a dealer scan it for codes may be the thing to do.. I have had many things show up, that 15 years ago would have been fantasy when the newer stuff is scanned.

              Also, a minor point: The OP stated 110/20, not 120/20


              • #37
                My typo - sorry. Had multiple windows open so I could see all that had been said with so many posts already it's confused by that alone. Charge known in this thing isn't known and diagnostics are going to fail or show erratic at best.

                New gauges said acquired might be faulty nothing to compare them to.

                Site is new with enough small details to fix also is making this difficult.

                General issues: It's a universal problem that people think they will solve everything with about a one line question vs paying a real shop for a diagnosis at least then decide if it's something to do yourself or is too involved both tools and know how to take on and A/C is high on that list. People think a two page read is all you should ever need for what is a trade all by itself where I am most full time shops don't do any A/C specific work at all if refrigerant is involved it just takes up costly room that doesn't get used most of a year but still costs to have it!
                MetroWest, Boston


                • #38
                  What I mean't was that maybe there is a code stored.... Of course since it's already been jumped. that may have messed that up.

                  Many times a dealer will scan for codes as a freebie.... Maybe not as a spoken rule, but I have had them not charge for it quite often.... Likely as it doesn't take much time/effort to do, and often will result in a repair job for them.


                  • #39
                    Codes can't hurt when there's a problem and true - can get most for free locally Autozone advertises free code readings may or may not show the full range of codes possibly stored but should show if it can communicate with the vehicle at all. I have to suggest that folks take free code readings like that with a grain of salt and decide for themselves what approach to take not just what a "store" to sell products might suggest right away.

                    Appreciate your help huntindog. As you see site is new but from a long history of very active A/C targeted sites free to use. Along with that also makes them targets for spammers, hackers of all sorts was the problem with prior ones - same folks that are available will or wont be here in time.

                    Just FYI - This like the prior versions of the same are 100% volunteer run with no motivation to see folks anything! Free all around.

                    This thread soon to be page 4 will make it just the much harder to follow the sequence of its progress for me at least.

                    I'm learning this format on the fly like everyone else too,
                    MetroWest, Boston


                    • #40
                      Yes I understand about learning this again... For awhile I could not find the login button.... At least on my computer, it appears to be part of the task bar, not the webpage.
                      That is something that could be keeping people from figuring it out.

                      Perhaps the powers that be, can make an adjustment.


                      • #41
                        We are in touch about the details. Upper right you see the arrow then click it drops down to log in or out. I suggested larger letters separately, "LOG IN" or "LOG OUT" if you are already in.

                        Details taken on as possible. I couldn't help with that if I tried. Also can't know the wild assortment of devices people might be using now never mind if it's friendly for another device than the omnipresent iPhone things. OMG - scary, they are everywhere.

                        Please suggest away something that's too hard or you can't find. Page 3 now who knows how that shows for you? BTW - I really can't look, read and type away if not a full page view like the laptop I'm using,
                        MetroWest, Boston


                        • #42
                          Sorry for the long silence, just got back from a 4 day trip to Maine.

                          I finally got a full day with minimal interruptions to trouble shoot the issue. Turns it out was a broken wire. The 12v wire to the pressure switch has corroded and broke. A big wiring harness passes from the underhood relay/ fuse block through the top of the driver side front wheel well into the car under the dash. My wife had previously managed to return from visiting her friends in Vermont with a missing inner fender. By the time I had gotten around to replacing it it was a couple of winter months. Sand and salt had been flung by the tire into the wiring harness. The sand sat in there and corroded the wires. Fortunately the only one that was affected with the AC wire. Quick solder job and should be good to go. With it reconnected I now get continuity to all the wires and the 12v I was expecting at the pressure switch.

                          I havent fully tested everything because half the car is apart, but I think it should solve my problems!

                          Thanks for all your help! Defintely couldn't have done it without the wiring diagrams.


                          • #43
                            Great news, and thanks for telling us the outcome. Often we never hear back and don't know if we helped or were totally off base. I would recommend, now that the system is working, to check the pressures and cooling. Like I said before, you might be a little light, but that wasn't what was preventing the system from starting. Pressure and temp reading should tell if you are full or shy a bit.


                            • #44
                              Same - great news you found it. Suggestion on the fix for wiring I do proactively is spray grease certain areas and with a flux brush with pure silicone grease cover items that could corrode as it doesn't wash out and rot wires AND doesn't cause a slight voltage drain at all.

                              Dang plastic shields are important and a pest many times to fix.

                              "Vermont" is no stranger to me whole area of New England has snow and all six states us copious rock salt more corrosive than battery acid! Horrible problems from that early on if driven it never mind missing shields so easy if snow banks you must drive over are frozen cause a lot of damage. Parts all over the side of roads around me just from that.

                              Normally I'd close out a solved thread but at the moment I don't have a know spot to click to do that. Not going to as that was a way to prevent new posts on YOUR thread and endless notices of a reply made ages after you care about this.

                              Apologize for site construction issues soon to be fixed I hope. If a problem please ask and I'll try to get it fixed. Not my site just here to help with now 3 prior failed sites to spam this one to be free of that,

                              MetroWest, Boston


                              • #45
                                I got everything buttoned up and ran the AC. Compressor kicked in right away along with fans. Air is blowing nice and cold. Compressor seems to cycle on and off appropriately. Pressure was 29 low, 150 high and it was 65F today. Seems to be about right according to the ballpark charts I found online.

                                Thanks again for the help and insight.