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Testing Subaru Pressure Switch

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  • #61
    This is the circuit I have been going from. To trigger the clutch I grounded pin 30 on the AC relay holder and the clutch engaged fine. From this I gather all the 12V supply wires are fine. Just to be sure I did run a separate 12V line to the relay. No improvement.

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    • #62
      Some pressure info: I "kick started" the compressor today by grounding the relay for about 10sec. After that the ECM takes over, the fans come on and all works fine. Stuck on the gauges:
      Low side reads 40psi, High side 260psi
      Drove to work, all fine
      Put gauges back on, same readings as above.
      Switch off the AC, Low goes to 60, High to 220
      Try to turn it back on, clutch engages for 3 sec and low drops to 40 disengages then increases to 80
      Maybe those numbers tell some of the experts out there something? I'm running out of ideas.

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      • #63
        I count about a dozen connecters on the coil circuit of the relay and at least 4 on the ground side of the coil alone. If I understand you correctly, you temp add a ground to the relay and then it stays on. SO I say again, I would be looking at the connections on the ground side of the relay.
        Pressures are within operating range for a working system, so for now I would forget about them. Your problem is electrical.

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        • #64
          Hmmm? Part look up didn't help if this really has a dozen connectors? Suggests multi-function run by ECM. Noted it was said known working relays didn't work when used in this.
          Captincanuck: Watch out for using 12v if it can touch the ECM you'll blow it! That should run on 5v then trigger what things do via relays with 12v is why you read info off a scanner when or if not clear just a compressor will not engage for now.

          Where power drops out is what to find.

          I'll list out some defaults that disable compressors on purpose on assorted vehicles many or just a couple.

          * Wide open throttle - no compressor
          * Engine too hot, shut down compressor.
          * Ambient temps way too low - disable compressor
          * Pressures/temps out of limits - disable compressor
          * High pressure or low pressure or temps out of range - shut down compressor

          Any of those sending bad info default is not to work is why I mentioned resets for assorted models. Some may require dealer's or a side of the ECM only seen or set/changed by that equipment will not show up on ordinary stuff readers for a fault code.

          ********************************
          Try testing ohms of the clutch coil. Look for close to 4.5 ohms not much higher or lower with it unplugged. If it draws way too much to operate that could be it but you said you didn't see power change there already which is another default or wire that gave out to find via ohm meter and or just looks like burned spot, stretchy spot or area. Harness may run any which way you will not find listed anywhere. Near hot exhaust parts possible not usual for this car but don't rule that out,
          Tom
          MetroWest, Boston

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          • #65
            each oval with a number next to the wire indicates a plug and receptacle with male and female terminals. each must be checked for resistance/voltage drop. This is the most likely area for the problem, next would be the wire itself, breaks in the insulation can allow corrosion to degrade the wire.
            You said you ran a new wire to the + side of the relay coil but that didn't change anything, what about the ground side?

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            • #66
              Originally posted by Tom Greenleaf View Post
              Hmmm? Part look up didn't help if this really has a dozen connectors? Suggests multi-function run by ECM. Noted it was said known working relays didn't work when used in this.
              I didn't mean there was a dozen wires to the relay, rather that the wire passes thru multiple bulkhead or inline connectors before reaching the end. Each connection is a potential source of a problem. Connections are always the weak link, and why the military spend thousands on connectors. Have you ever checked the prices on a Mil-spec plug or receptacle?

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              • #67
                So true - connections even early are a weak spot. Chase down which one loses continuity if need be when so and where. Not preferred is to poke wire thru insulation can work but makes yet another spot for corrosion down the road or feel wire - stretch it will by insulation only wire isn't intact inside.

                Then on to faulty signals telling it to shut down like a sensing anything is WRONG which hopefully a correct scanner would show incorrect.

                Mentioned clutch coils can even draw to much so connections if a weak spot get hot and fail. Goose chase for where what drops out or up to a wrong signal.

                Hair pulling but better than intermittent to hopefully find the fault. Possible some prior work on the vehicle disturbed or broke something and this went without notice for some time?
                Tom
                MetroWest, Boston

                Comment


                • #68
                  Originally posted by Cornbinder89 View Post
                  I count about a dozen connecters on the coil circuit of the relay and at least 4 on the ground side of the coil alone. If I understand you correctly, you temp add a ground to the relay and then it stays on. SO I say again, I would be looking at the connections on the ground side of the relay.
                  Pressures are within operating range for a working system, so for now I would forget about them. Your problem is electrical.
                  With the AC running I measured the circuit between pin 30 on the relay and ground. It showed no resistance (closed circuit to ground). I assumed from this that the ground from the line from the ECM to the relay must be intact? But I will trace to back to the switch and ECM today for good measure

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                  • #69
                    Originally posted by Tom Greenleaf View Post
                    Hmmm? Part look up didn't help if this really has a dozen connectors? Suggests multi-function run by ECM. Noted it was said known working relays didn't work when used in this.
                    Captincanuck: Watch out for using 12v if it can touch the ECM you'll blow it! That should run on 5v then trigger what things do via relays with 12v is why you read info off a scanner when or if not clear just a compressor will not engage for now.

                    Where power drops out is what to find.

                    I'll list out some defaults that disable compressors on purpose on assorted vehicles many or just a couple.

                    * Wide open throttle - no compressor
                    * Engine too hot, shut down compressor.
                    * Ambient temps way too low - disable compressor
                    * Pressures/temps out of limits - disable compressor
                    * High pressure or low pressure or temps out of range - shut down compressor

                    Any of those sending bad info default is not to work is why I mentioned resets for assorted models. Some may require dealer's or a side of the ECM only seen or set/changed by that equipment will not show up on ordinary stuff readers for a fault code.

                    ********************************
                    Try testing ohms of the clutch coil. Look for close to 4.5 ohms not much higher or lower with it unplugged. If it draws way too much to operate that could be it but you said you didn't see power change there already which is another default or wire that gave out to find via ohm meter and or just looks like burned spot, stretchy spot or area. Harness may run any which way you will not find listed anywhere. Near hot exhaust parts possible not usual for this car but don't rule that out,
                    Thanks for all the info. Will try to test some of these things ASAP

                    Comment


                    • #70
                      Originally posted by Captincanuck View Post

                      With the AC running I measured the circuit between pin 30 on the relay and ground. It showed no resistance (closed circuit to ground). I assumed from this that the ground from the line from the ECM to the relay must be intact? But I will trace to back to the switch and ECM today for good measure
                      Try taking a voltage reading between #30 and ground when the problem exists, use a digital or Vacuum tube meter (one with high impedance) and see if you see voltage. Once the relay has closed and the system is operating, the problem isn't visible, so make your checks when A/C is called for on the dash but the compressor is not operating due to the fault.

                      Comment


                      • #71
                        Originally posted by Cornbinder89 View Post

                        Try taking a voltage reading between #30 and ground when the problem exists, use a digital or Vacuum tube meter (one with high impedance) and see if you see voltage. Once the relay has closed and the system is operating, the problem isn't visible, so make your checks when A/C is called for on the dash but the compressor is not operating due to the fault.
                        With the switch ON and the system not functioning between terminal 30 and ground I measure 14.3V. This seems right to me as I'm reading the ignition ON power at FB-46 through the pressure switch and relay, correct? I also tried disconnection the pressure switch and measuring at 30 to ground. This should give any voltage from the ECM. I reads 1.52V. Don't know if that means anything.
                        Also measured the clutch resistance. With the leads on way it measures 2.5ohms, if I swap the leads around it measures 8.2ohms. I always thought resistance wasn't directional so maybe I am doing something wrong? Only 1 wire going to the compressor so I don't know how I could F this up.

                        Comment


                        • #72
                          With the switch on and the system not functioning, continue working back toward the ECM from terminal 30, check each connection, and I think you'll find one that is bad. You can't measure resistance while current is flowing in the circuit. Keep taking voltage readings and I think you'll find at one point it will drop to zero, from that point back up the wire to the last place you tested is where the problem lies.

                          Comment


                          • #73
                            Ohm checking a clutch's coil you can do off vehicle totally and should find one that reads closer to about 4.5 +/- a little. 8.2 is way too high and 2.5 to low. Check your reading on a know good clutch coil to see if it's how you tested or we may have found the problem? That check is with the thing unplugged not hooked up would confuse it,

                            T
                            Tom
                            MetroWest, Boston

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