• Login is located in the upper right corner of all pages.


No announcement yet.

AC Clutch and Hi Pressure (Discharge) Hose, Simultaneous failure...

  • Time
  • Show
Clear All
new posts

  • AC Clutch and Hi Pressure (Discharge) Hose, Simultaneous failure...

    SUMMARY: my AC clutch coil and discharge hose are both bad. How did that happen at the same time? 2006 Nissan Xterra

    Hi Folks, Newbie to the forum here, thanks for having me! It's quite rare to have two things fail at exactly the same time unless one precipitates the other. But my AC Clutch and Hi Pressure (discharge) hose seem to have done that. I'm wondering how they could be related.

    We've had our 2006 Xterra for 4.5 years. AC worked fine but had a slow leak, apparent a while after I bought it. I have AC tools, knowledge and a 30 lb cylinder of 134, so I added a little once or twice. Then two years ago exactly, in the Tucson July, I was driving at residential speeds and it blew the hi pressure, or discharge hose between the compressor and condenser. It actually had an oily spot before that near the crimp on one end which I thought accounted for the slow leak, and thus no surprise when it blew. I quickly got a replacement, installed it along with 1.5 oz make-up oil (PAG 100), evacuated and recharged, all good. Worked great through two Tucson summers, but in the last month I noticed poor cooling. Put the gages on, sure enough, low on refrigerant. Huh, I wonder where this slow leak is? I recharged it up to pressures per the FSM, and it was cooling great.

    My wife and a friend took it on a road trip, but ~200 miles in on the first day, trouble struck. They didn't notice poor cooling performance on the road, but then they went down a dirt road a ways and stopped to walk around. Ursula's friend is from Vermont and not used to the heat in AZ / NM, so she went back to the car and started it. She said the AC did not cool at all; she fiddled with it for, dunno, maybe 10 minutes, and then there was a sound and vapor came out from under the hood. Ursula, a good distance from the car, thought she heard a screech. Sharon, in the car, did not hear the screech but a pop consistent with a hose blowing.

    After waiting a while and establishing that the engine was fine and not overheating, they drove back home, rented a car and left again the next morning.

    So the 2-year old discharge hose is blown wide open at the end of the rubber nearest the compressor. I got another one and went to replace it. Before I did that though, I ran the Auto Active Test that cycles a bunch of stuff on and off to validate function, including the electric fan high and low, and the compressor clutch. Engine is off for this test. The fan and everything else were fine, but the clutch was not clicking. Huh, I removed the airbox to access the compressor. The single hot wire down to the compressor is fine visually, but after disconnecting shows an open circuit from the connector pin to ground (it should have a few ohms through the coil). This would normally indicate an open clutch coil, I've had that happen once before on our Mini Cooper. But another strange thing: that wire pigtail on the compressor side is about 4" long going into the clutch coil. It goes through what appears to have been a plastic holder, which is melted. The wire insulation is NOT melted and the wire is not shorted, nor does it feel broken in any way, and I don't see any other melted plastic.

    Finally, I removed the belt and turned both the AC pulley (freewheeling) and the compressor (via the hub) by hand. Both feel smooth and normal.

    I'm really struggling to figure how this would have happened. The hose, maybe it was just bad when new. I thought it may have gone like this: it probably leaked down some after the recharge (faster than I realized), and combined with being parked in the heat it was not cooling off for Sharon. But it was still spinning the compressor, trying to cool with insufficient 134, when the high side hose let loose due to being defective. But that scenario does not fit with the open clutch coil, and doesn't make any sense of the melted plastic. But if the clutch coil went first, how did it blow the hose?

    Could the hose have shed a piece of rubber inside during failure that got caught, maybe at the condenser fitting? This caused a pressure spike which blew the hose, and somehow put brief additional electrical load on the clutch, burning it out? I'm really grasping.

    Ideas? Thanks, Jeremy​

  • #2
    Many things "could" have happened here. What the exact cause will take some research. Common thread seams to be excessive pressure.
    No where did I see a condenser replacement, so that is suspect. You did check the fans, and I assume that you checked them for proper speed.
    Some clutches have a thermal fuse in the winding itself. It blows when the clutch start to slip, the reason is to save the belt, which often drives other components that will leave you stranded if it breaks. Better no A/C than being stuck in Death Valley with no A/C and no working car to get you out.
    Some systems, but not all have a pressure relief that "hopefully" will pop off before things blow, but they are not 100% foolproof.
    Sitting still out where it is hot, the A/C has to rely on the fans to move enough air over the condenser, the condenser being in good enough shape to take the heat from the refrigerant and transfer it to the fins, and air.
    Without knowing what the pressure and temp readings are there is little more that can be deduced from you post.
    Assuming, the charge is correct by weight, the temp and pressure readings will be key to finding out what is going on.


    • #3
      Also re reading, I noticed you checked the fans with "auto active" but did you confirm they came on with the A/C when needed?
      Some fans run all the time a/c is called for, and some run on a pressure switch, defective pressure switch, or transducer and the fans don't come on when needed and pressure will spike.


      • #4
        Thanks for the response.

        Condenser: I have not replaced it. I can tell you it has visual signs of age; the more exposed area has bent fins. It's fairly clear of debris otherwise, but I'll hose it out. Do you ever use the spray cleaner that they sell for home AC units? When the system has good charge it cools quite well, even in hot weather, which is evidence that it may be fine (and that the system in general is, or was, quite functional). It could possibly be the source of a slow leak.

        Fans: it has both an engine driven main fan and electric aux fan. Main fan, I installed a new, factory clutch recently. Electric is functioning at both speeds. Shrouds are intact. And yes, operating AC at idle in high temps is not a recipe for peak performance and can be hard on the system. I actually avoid it. In this story though, Sharon reports that it didn't cool at all when restarted, which makes me think it had already leaked down, but that's not for sure.

        Overpressure protection: per the FSM, the pressure switch cuts out around 400 psi, and the popoff valve ~430. In theory the cutout should be at a pressure the rest of the system can handle, right?

        Clutch coil thermal fuse: OK, that's big news to me, I didn't know about that potential feature. It at least gives a mechanism for both failures to happen at once, even though the precise timing is still kinda mind blowing. It explains the screech my wife heard. Either:
        1) a piece of the hose broke loose internally, caused a blockage and a pressure spike, causing the clutch to slip and get hot, blowing this fuse and the discharge hose, or
        2) maybe it had not leaked down and had full charge. Sharon's perception of "no cooling" was not entirely correct, but it was hot and the system was struggling at idle, building high temps and pressures. Still weird that the clutch slipped and hose blew at the same time though, unless something internal caused a blockage.

        Charge and pressure performance numbers:
        When I replaced the hose before, I put in the FSM-specified 1.5 lb. Other times, topping off I only used the gages. Note, in general I find that when the low side and air temps are right, the high side is always higher than the manual specifies, not just on the Xterra but on any vehicles I've worked on. I'm in AZ, so it's hot, but I have a evap-cooled and insulated garage that is usually around 80-85 deg when it's HOT outside. If the tables include ambient temperature I use the correct one for that temp, and humidity if possible. High side always runs maybe ~50 psi higher than the book says, and that's never caused a problem. If I use less freon, the low side is very low and the vent temps are too high. I'm considering that maybe I habitually overcharge by some margin. That said:

        Click image for larger version  Name:	image.png Views:	0 Size:	14.2 KB ID:	4702

        Any more thoughts? What to check / replace? Thanks!​
        Last edited by GearheadS; 07-29-2023, 02:45 PM.


        • #5
          Originally posted by Cornbinder89
          " but did you confirm they came on with the A/C when needed?
          The FSM gives a diagram of when the electric fan comes on and at what speed, related to both AC hi side pressure and engine temp. It seems to operate normally, but I did not measure precise temp / pressure cut on and off points.


          • #6
            Temp/ pressure charts are available here:
            R-134a vs R12 Temp Pressure Chart (http://www.acsource.net/acforum/viewtopic.php?f=1&t=8490#p30284) Postby ACProf (http://www.acsource.net/acforum/memberli

            Looking at your 2023 numbers I see a condensing temp of 141deg F with ambient of 82! Air cooled condensers should be in the range of 30-40 deg hotter than the air passing through the condenser, You are showing close to 60 deg, and that is at 82.
            In theory, the closer the condensing temp is to ambient the better, in practice air cooled condensers aren't that good, 30 to 40 deg difference is considered acceptable.
            The most common causes of high condensing temps are:
            1) overcharge, the extra refrigerant backs up in the condenser reducing the surface area available to cool the hot gas.
            2) degraded condenser where the thermal bond between tube and fin is poor, the heat can't make it out to the fin and be carried away. Even condensers that "look" fine can have a problem. You should be able to feel with your hand how hot the fins are, and the outlet tube of the condenser shouldn't be warmer than the fins.
            3) air flow problems, if air is not passing the fins at a high enough rate, the condenser can't do its job.
            As to the reason the system didn't pop off,
            1) it is possible the relief is stuck closed
            2) the switch that shuts it down is likely the same one that is supposed to turn on fans, so that could be a problem.
            3) if the high pressure cut-off does work, it will cycle back on when the pressure only drops a bit, forcing the clutch to start the compressor under full load. If the clutch can't or slips it may open a thermal fuse in the clutch coil (if so equipped).

            The FSM high side numbers reflect a condensing temp in the 30-40 deg range above ambient.
            I believe the drier is in the outlet of the condenser on this vehicle, replacing the condenser at this point in time may not be a bad thing regardless, new drier bed comes with the condenser, and you eliminate poor fin to tube bond as a problems. I looked at Rock Auto, and they are about $120 or less, (good quick site to look up what is used and a available)


            • #7
              OMG, AZ heat, no response from clutch coil? Long read, sorry if I missed it. Clutch engaged was slipping?
              If so when working that makes glowing heat! Coil wouldn't make it IMO.
              Assorted vehicles use that thing that melted or use fusible link wire.

              Condenser needs to be free of dirt, bugs etc. in between it and radiator too.

              Keep at it that heat is excessive stuff will fail. For now coil may be harmed if was new?
              The slipping could be large air gap? Heat reduces magnetic power then slip wore it.

              Just thinking as I type check that air gap guess not over .25 is about a tightly folded biz card!

              Stinks, just check everything again for now coil may have gone nuts.

              Right at it from memory average ohms ~ 3.5 you got nothing thru wire go right to it if on a bench would test not zero,
              MetroWest, Boston


              • #8
                Thanks for the insight on the delta T between the air and the condenser (as measured via pressure). I'd say, looking back, that overcharge was likely involved, but not the only thing. My question on high condenser pressures is, since I've routinely measured them high, but bringing them down means a "too low" low side, what's the deal there? Maybe my gages are bad? Although when the system is sitting at rest, say 80-100 psi, they read the same.

                Yeah, maybe it's time for a new condenser, just cuz. You used to routinely replace the receiver / drier (which had a sight glass, those were the days), and you are correct it is built in to the outlet side of the condenser. I've had the system open twice with this condenser, and I don't know the history before that. I don't like to throw parts at a problem, but this sounds like good wisdom.

                You are correct that there is only one pressure transducer. I have anecdotal observation that the fan works "approximately normal", but no hard evidence that the transducer is good.

                Tom, the mystery is that the discharge hose AND coil went bad, apparently at the same time. Yes, 3.5 ohms sounds about right to ground, and I'm getting OPEN. I have no reason to believe the clutch was slipping any time before this event.

                Obviously at this point I need a coil and a discharge hose. Maybe a condenser / receiver. How do you check for overcharge, other than gages or weight? Is there something to observe, temperature-wise, on the condenser?

                Thanks to you both!


                • #9
                  Re high side pressure:
                  You are not lowing the charge to bring the pressure down.
                  The pressure show the temps things are happening in the system, so they really show how well the system is moving heat, not showing anything in regards to the state of charge. Obviously, if the state of charge is off, how well the system moves heat will be off from ideal it can be. SO pressure can show something is wrong, but not tell you if that is because of the charge or other reason.
                  This is why it really needs to start from a known correct charge.
                  If your number have always been high, esp right after the known correct charge is in the system, that points to something other than charge being the cause.
                  You want to see the correct pressure with the correct charge in the system, you don't lower the amount to bring the numbers where you think they should be.
                  If you know your system and its condition you can make a stab at "boosting" a slow leak, but it is only a guess. I know we all have done it at some time or another. I am not condemning the practice, but when you have a problem, you have to start from a known correct charge in order for the pressure readings to tell you anything.
                  If I understand you correctly, your high side has always been high, even after a known correct charge.
                  This would point me at the condenser not getting the heat out very well.
                  When it is at idle, and not cooling very well, you can take a hose and spray the condenser and that will act like the condenser is much bigger or better. You should see a fall in both high and low side while the condenser is water cooled.


                  • #10
                    And if the water trick makes the pressures more in line with spec, that points to an inefficient condenser?

                    I see your points. What I am saying though, about "too high" high side, is I have measured that on multiple vehicles over many years. When the low side and vent temp are right, the high side is ALWAYS too high on many cars. Thus, I had come to accept it as "normal". I don't know how to explain it.


                    • #11
                      Possibly easy question: does the receiver built into the condenser have a filter of some kind? If there was a sudden blockage from, say, a failing discharge hose chunk come loose, where might it get stuck and block the high side? If that's somewhere in the condenser it will be fully mitigated with a new one. If that's the expansion valve...well that's another story of course; it's under the dash inside the car


                      • #12
                        My computer is going screwy - heavy storm coming thru - bear with me.
                        These blown out hoses may be a quality issue. IDK if they can choke inside meaning separate in shards?

                        "Brake flex hoses" do that would be a first to hear about but is why your here. Gaseous pressure isn't like hydraulic pressure yet you are getting those type issues?

                        While this device is still working leaks are a given with time pressures for how much is not it, starting from empty/full vacuum then they mean something.

                        Again - these temps are pushing limits of what things should tolerate and are here too more 100F+ days than I recall but it does every year not this long.

                        I just don't know what that could mean to this with certainty. New England has more shade than the SW of US actual temps driving along changes I watch that.

                        So back to what this would do to front of compressors just sealing a spinning shaft is the weak link but leaves oil evidence I guess you'd have to degrease it to see if new is there.

                        Carry on you two I expect power out it's just ugly out there right now,

                        MetroWest, Boston


                        • #13
                          Yeah, brake hoses are where I've seen internal blockage due to hose breakdown.

                          Here are two pics with and without flash of where the coil wire goes into the coil. Is that white plastic rectangular thing a thermal fuse?



                          • #14
                            The condenser has a moisture filter bed, but it doesn't do anything with debris. The multi-flow condenser tubes are so small they would plug first, not that I am saying that is the problem.
                            You should be able feel the condenser, there should be even heat that slowly decreases from inlet to outlet with no cool or hot spots.
                            I would worry about the clutch connector if the clutch is pulling in, if not then look closer.
                            If you suspect your gauge is inaccurate, then compare to another or replace with a new gauge from a reputable supplier.
                            As it stands, the 60 temp difference between ambient air and condensing temp and the symptoms seam to match up with not shedding enough heat at the condenser


                            • #15
                              Originally posted by Cornbinder89
                              You should be able feel the condenser, there should be even heat that slowly decreases from inlet to outlet with no cool or hot spots.
                              I would worry about the clutch connector if the clutch is pulling in, if not then look closer.
                              Ok, thx. Lil tough to feel the condenser since the system is out, lol. Tough to feel it even when it's working as hand access is limited.

                              The clutch is definitely inop, and has open circuit to ground as mentioned. I suspect that white rectangle in the pics above are the thermal fuse, and that it's blown.


                              • #16
                                Agreed - no clutch engagement. Back to your pics of burnt wire to probably a thermal resistor.
                                Just for laughs - not funny found a pic of it on eBay here "> https://www.ebay.com/itm/15424992481...Bk9SR4Kis9y0Yg <"

                                Whole clutch available that one pricey just an example. Some you just remove or need a puller tool pics didn't give me good clues.

                                See if that's a match at least your pic the wire was crinkled isn't right so now IMO no good but IDK if the problem or a result yet?
                                MetroWest, Boston


                                • #17
                                  Tom, here's a screenshot of one of the pics in the ad you linked. I think the thermal fuse is the part I circled in red, yes? Also, the part I circled in blue is a plastic or rubber strain relief on the wire that is melted, although the wire itself is not damaged.

                                  Have you guys seen expansion valves get plugged with debris?

                                  You guys have helped me greatly to understand aspects of the problem, thank you! But I still don't really have a root cause for how the two components failed together. I am thinking about replacing the discharge hose, clutch and condenser, and give it a try, taking great care to get the freon quantity correct. Then I can make observations about the pressure readings and my gages, etc. Does this seem like sound reasoning?

                                  Oh, one more. In your experience is it ever helpful for people in really hot climates like myself to add an extra small pusher fan on the front, perhaps in a corner of the condenser that seems under-served by the stock fans?

                                  Thanks again!
                                  Last edited by GearheadS; 07-30-2023, 09:48 AM.


                                  • #18
                                    Originally posted by GearheadS

                                    Ok, thx. Lil tough to feel the condenser since the system is out, lol. Tough to feel it even when it's working as hand access is limited.

                                    The clutch is definitely inop, and has open circuit to ground as mentioned. I suspect that white rectangle in the pics above are the thermal fuse, and that it's blown.
                                    Ok, thought the system was in-op due to burst hose. My bad.
                                    This is going to get expensive very quick. DIY may not be the cheapest out.
                                    When I did a quick check of what R-A carries, they didn't list the clutch separate from the compressor, that doesn't mean you can't get one, but is going to take searching. Omega and other A/C parts suppliers might sell the clutch alone. Then there is the hose and condenser. Special tools to get the clutch off, and while you gone that far, the front seal should be replaced (enough heat to melt the fuse in the clutch is enough to possibly damage the front seal), so that may make compressor replacement the easier if not cheaper option.
                                    As you so aptly pointed out, you can't diagnose further until the system is back operating, so impossible to do in one shot with any confidence. You can throw parts at it a hope you nail it when the system is apart, but if you don't get it the 1st time, it is more money.
                                    Condenser is a good possibility, but it could be something more esoteric like reduced air flow through the condenser from degraded or missing air seals around the rad and condenser, missing air dams , or any change or damage that changes the air-flow. even decreased fan speed from a motor with dried out bearings.
                                    If it does fairly well at highway speeds, that points more to air flow problems then bad condenser, (a condenser doesn't get better at higher speed, air flow does) but that isn't 100% proof of one over the other, because better air flow can help the working parts of the condenser move more heat to make up for the in-op parts of the condenser. This is where running you hand over the tubes and fins looking for hot and cool areas comes in.
                                    The sad part is: many shops you take it too are going to attack the major problem they can "see" (bad clutch/ bad hose) and not dig further until it is brought back again.
                                    Refrigeration is a difficult thing to diagnose because the "system" is "free floating", that is everything is dependent on everything else to remain in "balance". Reduce the heat transfer in one place, and all the pressures and cooling change through out the whole system. It is not possible to see a pressure change and point to one thing it must be, all you know is that it isn't correct. You have to work through the possibilities and eliminate them as a the cause one at a time. If one thing is "sort of" working, you have to determine is that the problem or the result of something else. There are very few definite in refrigeration, it is a lot of making sure something is NOT the cause until you are left with what is. When there is more than one thing that is the problem it becomes infinitely more difficult, as you have more things that can't be eliminated as the cause.
                                    Accurate gauge is paramount, if you can't trust you gauge to be correct, have it calibrated or replaced, so not to chase your tail with wrong information.
                                    Temp reading only matter where they pass through the coils, the thermometer in your back yard is not where the condenser gets is air, you need to know the air temp right in front of the condenser to make a judgement on high side pressure reading. I don't use or trust IR thermometers, I have been fooled by bad readings enough not to use them at all.
                                    All this is why it is common to read where someone replaced every component and hose in the system trying to resolve a problem, and may or may not be successful. If there is an air flow problem, replacing the condenser isn't going to change that. It can be a frustrating and expensive job.


                                    • #19
                                      Another point:
                                      Since you have had hoses fail before, if it were me, I would put a switch port in one of the high pressure hoses and an high pressure cut off switch on the port, at least until I got the system sorted out. I might use a relay between the switch and compressor, so I could put a pilot light on the circuit to know when "my switch" is shutting the system down, and not the mfg safety system. That way, if you know the psi the switch you put in trips, you can know what the system is seeing at that moment.
                                      Where you live, and the air temps you have, 395-400 psi might be seen, Anything over 400 psi and it is hard to keep hoses on fittings. In the upper mid-west I would use 375 psi as the trip.
                                      Hopefully by doing this, you don't blow the hose off while searching for the problem, the system just shuts down.
                                      The only other way to know the pressure is to leave the gauges on and strap to the windshield when you are driving looking for the problem. Often the pressure will rise faster than you can react and turn off the compressor, so a switch that does that automatically is a help.
                                      Not only can it save hoses, it can save clutches and belts, although if it trips and re-sets often the repeated clutch trying to start a loaded compressor and still burn the clutch, but if you see it happening (via your pilot light) you can turn off the compressor for a longer period and let the pressure subside,


                                      • #20
                                        RE: Post 17 Yes gearhead - that's what your pic showed. Refresh, if that's what you have clutch comes off with one bolt! I think other things there are shims to set gap?

                                        As we are saying it's HOT or was where you are never mind the garage moderated temp.
                                        I like ideas like a monitor light just said.

                                        Already said my area was hot too over blacktop no light roads stuck in traffic OMG it's not the weather is/was time of year highest sunlight.

                                        Other thought while we beat on this is something Nacho (is here just not much) pointed out backwards radiant heat from cooling system's radiator. He's in Hermosillo, MX (HOT CITY) is clever.

                                        I just worry about adding fans that you said? Aux fans may not help fighting with each other need to really know it increases air flow goes down and out.

                                        Means if an air dam isn't there (busted ones here on sides of lousy roads) air moving along will try to go under cancelling the flow!

                                        Sorry we are all verbose with this by chance worked for other shops to find the screwed up things they didn't have the time, I did. I was alone sometimes no work could test drive the cars they couldn't leave to do that!

                                        Odd I also can heat my small shop to ~100F in winter make a system work + hard can easily be well below zero out how could anyone know something worked?

                                        No more I'm tired have so much else to fix non auto that's enough.
                                        I really want to see this fixed if it takes something creative for extremes cars just don't blow hoses like you said - twice!
                                        MetroWest, Boston