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1998 Ford ZX2 - A/C clutch only engages when high pressure switch disconnected

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  • 1998 Ford ZX2 - A/C clutch only engages when high pressure switch disconnected

    I did some A/C work on a 1998 Ford ZX2. A/C had been out for several years due to a bad compressor seal. I replaced the compressor, receiver, condenser, manifold tubing and the orifice tube. Flushed the rest of the lines and pulled vacuum for several hours. Replace the PAG refrigerant to spec.

    A/C worked great for about two weeks. The one day it blew cold for a moment and then just straight ambient air. The A/C acted a bit flaky, and even got stuck on when the manual HVAC controls where set to vent only.

    When initially switching the A/C on, the clutch will engage for about a second or two then it will disengage and remain that way. I ran a few tests. Jumping the clutch caused the A/C to blow cold. Jumping the low pressure switch did not cause the clutch to engage. Static pressure was around 105 psi for both high and low side at nearly 90 degrees outside temps. Jumping the clutch, the pressure was around 40 psi low side, and 250 psi high side. Now here is where it gets weird. If you open the throttle the clutch will engage for several seconds, and even the air will start to blow cold. I got curious, and disconnected the high pressure sensor. Once it is disconnected, the cooling fan goes into high speed and the clutch engages and the air blows cold. Any ideas?

    The CCRM (which houses the a/c relay) is notorious for failing on these cars. The a/c relay often comes loose at the solder joints or even melts and fails. However, I have replaced this relay in the box, and I even have an extra good box on hand, and both seem to function fine and a get the same results as above with either box.

    Thanks ahead of time.

  • #2
    What is the Clutch gap? I am wondering if the gap is too wide and rev'ing the engine brings up the voltage just enough to pull in? The other is that the high pressure sensor is faulty. I have no (read 0) experience with the model in question so may well be "off base".
    May be Ignacio will stop by and he may (will) have more experience on the model in question.

    Comment


    • #3
      I really don't think it's the gap. I can get it to engage by jumping (even with the car off) and by pulling the plug on the high pressure switch.

      I think that the A/C systems of that era of Ford fundamentally operate in the same manner. But, I could be wrong.

      Comment


      • #4
        Could be, but my experience is with older heavy trucks (Semi tractors) and old Tx systems in general. I own a '99 Explorer but haven't had to dive into yet.

        Comment


        • #5
          Another tricky one left to some guessing. I would check the gap just because and spec is almost always (any brands) about .020 will work on most up to about .035 or so and be erratic at first.

          Why unplugging the HPCO allows it to work suggests anything about wiring to that switch and the plug itself. Watch out with testing only with DVOM or LED test light no jumping those as you could back power control module and wreck it and it might be already? Defaults should be compressor OFF if anything wrong and inplugged now and working there's clearly something wrong - wires, plugs anywhere it goes already said it's messed up connections checked with another so problem stuck somehow to allow it to work not sure how?

          Probably will take a scanner and readings with very costly equipment would like to see what codes is shows as a direction. Can just speak basics without full date for the particular vehicle but many are DISALLOWING a ground not adding power for things to operate which is against what you might think. Add ground and it will work so why if that's how this one is sending a signal not getting thru or defaulted (burned something out) to not cut off when it's supposed to.

          HPCOs vehicle by vehicle can't know without pro edition info how much it controls. Many will also signal to turn on fan(s) and at what speed from the signal it sends plus cut off compressor at out of range pressure meaning too high supposed to quit so you don't blow out pressure relief valve as the only safeguard with all 134a from new cars at least,


          Tom
          MetroWest, Boston

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          • #6
            Thanks Tom

            Gap on the clutch is within spec. I did not try to jump the HPCO as it is a three wire switch and I am not sure of the exact function. I will probably make a pigtail with leads that I can probe with a DMM. My understanding is just as you stated; the signal prevents ground. I also agree, it doesn't seem logical that pulling the plug on the HPCO would allow or cause the the clutch to engage. I still find it odd that the A/C got stuck on for a few seconds after switching to just the vent settings.

            Comment


            • #7
              ? This could be a real wire chase and cause of hair loss! You said it engaged with just "vent" request for a short while? There's a clue there somewhere as to where to look for a wire that grounds to engage compressor that has rubbed thru insulation type thing - maybe?

              Here's the snag for me still thinking on this. Even full wiring diagrams of every wire and where it goes isn't going to show you location or proximity to something that would mess with the wire. Unplugging you could look close by the plug but now doesn't explain same wire(s) are disturbed from the control head.

              My attempt at some logic is the wire that triggers relay from possibly 5v (reason you don't go jumping things) for computer is picking up ground enough somehow. I think I might go to the relay and physically chase that wire back wards no doubt routed thru the sun visors or who knows - kidding on that. May get too close to some exhaust heat somewhere or harness hidden in the plastic type stuff with a split to look inside where it could move.

              You could even get factory code readings that probably would show something but could be misleading. Do remember codes if found DO NOT SAY which item to replace just the circuit that's showing the fault. I'd go looking first from the relay backwards hope it's obvious and no other damage to controls involved,
              Tom
              MetroWest, Boston

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              • #8
                Idle speed should be between 850 and 1000 rpm for the engine to sustain the compressor working. These cars suffer from annoying engine vibration at idle. This vibration causes a lot of false contacts all over the system. I happen to have a '98 ZX2. If you need a diagram, let me know.

                Comment


                • #9
                  Originally posted by Nacho View Post
                  Idle speed should be between 850 and 1000 rpm for the engine to sustain the compressor working. These cars suffer from annoying engine vibration at idle. This vibration causes a lot of false contacts all over the system. I happen to have a '98 ZX2. If you need a diagram, let me know.
                  If you could provide the diagram, that would be great!

                  Comment


                  • #10
                    The plot thickens a bit. I was looking around under the hood to see if I could find any issues. I didn't notice anything much, but at some point I did spin the radiator fan blade by hand just out of curiosity. It didn't seem to spin as freely as I thought it might, so I started doing a few internet searches about that. At some point I came across a video that detailed some issues with overheating and lack of a/c on a late 90's Saturn. I don't have any overheating issues at all, but in the video it was mentioned that a way to test the radiator fan on the Saturn was to pull the plug on the ECT (engine coolant temperature sensor). So I decided to try it on my Ford.

                    As mentioned before, if I turn on the A/C with the plug on the HPCO disconnected, the radiator fan comes on at high speed, the A/C clutch engages and the air blows cold. So, before doing the test for the radiator fan as mentioned in the video of the Saturn, I plugged the in HPCO. Now here is the interesting additional information. I disconnected the ECT, started the car, and sure enough the radiator fan turned on at high speed. The "service soon" idiot light came on too. I had no reason to think the ECT was bad, I was just playing around. But our of sure curiosity, I decided to try to turn the A/C on...and what do you know? The A/C clutch engaged!

                    So, I have a situation where pulling the plug on the HPCO cause the radiator fan to run at high speed and the A/C works. But the A/C also works if I plug the HPCO back in like it should be, and then pull the plug on the ECT. In both cases the radiator fan runs at high speed and the A/C works! So now I am wondering if for some reason the radiator fan is to blame or is another symptom of the same problem. Is the radiator fan not operating correctly which in turn makes it so the PCM won't allow the A/C clutch to engage as a result? Could the ECT be bad in a way that it doesn't throw a code, but somehow prevents the A/C from working?
                    Last edited by Orion; 08-20-2017, 11:09 PM.

                    Comment


                    • #11
                      Quote from first post " The a/c relay often comes loose at the solder joints or even melts and fails."

                      Now you found fan that doesn't spin freely - that's a cause to draw excessive current and wreck an unknown amount of wiring, cause confusion and your intermittent results from an assortment of tests.

                      Can call this vehicle about a 20 year old now and if adding overheating to it (engine) can be fatal to be cost effective to have this as just a car that runs at some point.

                      If you don't have the diagrams yet from Nacho ask again. Somehow or with another person to look and test find out if you are just "beating a dead horse" with this.

                      It's all over the place with problems. We aren't there is a huge disadvantage. The web to fix this or decide to continue trying I doubt be the answer to whether you should invest or cut losses. I suggest getting pro help to make that call just the overheating you could easily end up with not engine worth fixing? No engine, no A/C.

                      Decision time on the car as a whole,
                      Tom
                      MetroWest, Boston

                      Comment


                      • #12
                        Originally posted by Tom Greenleaf View Post

                        It's all over the place with problems. We aren't there is a huge disadvantage. The web to fix this or decide to continue trying I doubt be the answer to whether you should invest or cut losses. I suggest getting pro help to make that call just the overheating you could easily end up with not engine worth fixing? No engine, no A/C.

                        Decision time on the car as a whole,
                        Tom, like I said, I have zero overheating issues. Temps stay solid, and have been the same for years. It's just that if I disconnect the ECT, the A/C magically works as the ECU forces the fan into high speed as a default protection. Gauge sensor and ECU sensor are separate on the is car, so I know exactly where the temps sit.

                        Car only has 75K on it, and has been very well taken care of.

                        Comment


                        • #13
                          Sorry if anything misread. You said quoting you "I didn't notice anything much, but at some point I did spin the radiator fan blade by hand just out of curiosity. It didn't seem to spin as freely as I thought it might,"

                          If that motor is erratic even getting low voltage too much then snap out of it there's been high risk with that. You are there, I'm not so at a total disadvantage. The wiring issues just aren't helping me think this is messed up in assorted ways not convince accurate anything about proper running order all the items needed could get nasty costly and still need A/C something?

                          I still can't explain why it runs with HPCO is unplugged so what else is lurking if not obvious, yet?
                          Tom
                          MetroWest, Boston

                          Comment


                          • #14
                            I might go back and visit the notorious CCRM (constant control relay module). Even though the relay was replaced, I am now suspicious of it's operation. The WAC relay in the module is what typically goes bad or has a loose solder joint and causes the A/C to fail. My symptoms are a bit atypical of that known problem, but it is the only thing I can think of that ties everything together. If I can force the radiator fan on, then I can get the A/C to work. The relay is PCB mounted 5 pin. I might just remove that relay from the board and wire a 5 pin pigtail into the board so that I can be sure of good solder connections and I can replace the relay at will. As it is right now, I can't see under the PCB mounted relay. There might be a loose or bridged connection.

                            Comment


                            • #15
                              Originally posted by Nacho View Post
                              Idle speed should be between 850 and 1000 rpm for the engine to sustain the compressor working. These cars suffer from annoying engine vibration at idle. This vibration causes a lot of false contacts all over the system. I happen to have a '98 ZX2. If you need a diagram, let me know.
                              Hey Nacho,

                              Any way you can get the diagram to me. It would be great if I had a schematic and pin out on the CCRM.

                              Thanks a bunch!

                              Comment

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