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  • Misbehaving clutch cycling switch

    My 73 Blazer has had a non functioniing clutch cycling switch.. It is new, as is everything else in the system.
    The new switch has never cycled off, even at really low vent temps of 32.5. After much discussion and thinking about it, I decided to leave it as is for awhile. Being in Phoenix AZ, it isn't a huge problem.
    This morning I was on the highway about 4AM, Ambient temp was about 88. The vent temp got to 37.8, and my clutch cycling status light stated flickering really fast. ( I installed this and a clutch shutoff switch some years back when I used to tow with it)
    It is a great way to see just what is going on with the clutch..
    I surmised that the switch is trying to work now. I think that as an R12 switch, it may have set on the shelf for so long that it became stuck, and is now working it's way loose.

    My concern is that it may over heat the clutch with the rapid on off it is doing, causing it to slip. I turned it off a couple of times with the manual switch, and it went right back to the flickering light.
    I am considering just jumping the switch terminals for a few days to see if the switch will settle down and start working normally. Since it's been running awhile with it non functioning, there would be no real harm right now. I also considered just replacing it, but it's replacement may well be in the same condition.

    I estimate that the evaporator temp was right around 32 this morning when this occurred...

    Thoughts?

  • #2
    So... is this an orifice tube system? I would have thought it was a VIR or Tx system with a frost switch, Somewhere I have a '73 Chevy truck manual but can't lay my hands on it right now. Anyway you cut it, there is supposed to be a difference in cut-out cut-in temps/pressures to prevent short cycling. IS this a temp operated switch? I would think so given the year we are talking. Calling it a "clutch cycling switch" is confusing me, makes me think it is a pressure operated switch like in a CCOT system.

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    • #3
      Ever think of installing a dash-mounted toggle switch to turn the compressor off and on? If your evaporator temperature is really low like 32F, then on days when we do have some humidity, you could get ice freeze up on your evaporator.

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      • #4
        I think he has that and a pilot light, he said he added that when he towed a lot with the Blazer

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        • #5
          Heard of the rather toasty temps in your area! Hey - great to have the cool and probably get away with it as air pretty dry there - Phoenix. Verify that vent temp with another thermometer. You said 37.8 later at 88F ambient would be plain excellent but really shouldn't stay even there.

          Do you have the old switch? Check - it's old enough I can't remember but should screw on with just a rubber O ring. The old one would show that inside it could to just that so you don't lose your charge the reason being it's probably adjustable! I could be wrong but think tightening will raise cut out pressure. Just go 1/4 turn no more at a time if you try that.

          Watch out! IF there's not Schrader it will blow out all refrigerant you don't want nor get hurt. It would hiss even if you remove them fast just a very short time then quit you know you are good to check while charged.

          Check real temp of air coming in thru grille not just that forecast temp. Road surface could be a LOT hotter so this is exceptionally cold output if higher air temp than you thought.

          BTW - A couple times put the Ford from the 80s common larger mushroom cut out switch with plug if used so be it either spliced in or lease OE and make up good wire just spade terminals definitely adjust. There a risk in doing that it could leak so check.

          Cycling clutch? Check the air gap and set to close if not. About .020 is a standard or folks would say a folded standard business card paper would be snug.

          Trivia: If clutches friction surface is hot from cycling it's losing magnetic force to pull it in or keep it engage may cool and be more magnetic! Funky but the hotter the metal the less magnetic! A maybe to rule out and might need checking function of the clutch of its coil,

          Tom
          MetroWest, Boston

          Comment


          • #6
            Originally posted by Cornbinder89 View Post
            So... is this an orifice tube system? I would have thought it was a VIR or Tx system with a frost switch, Somewhere I have a '73 Chevy truck manual but can't lay my hands on it right now. Anyway you cut it, there is supposed to be a difference in cut-out cut-in temps/pressures to prevent short cycling. IS this a temp operated switch? I would think so given the year we are talking. Calling it a "clutch cycling switch" is confusing me, makes me think it is a pressure operated switch like in a CCOT system.
            You are correct. It originally had a temperture probe into the evaporator. Those did not seem to be all that reliable, and now seem to be unavailable. So I installed the clutch cycling switch instead into the accumulator. Like I said, it was new along with everything else about 6 weeks ago. But it never worked.

            In am figuring that it is trying to start working now. Probably been sitting on the shelf for years and got stuck. (R12 switch)Since under my present conditions, it really isn't critical, I came up with the jumping it idea. Perhaps with some more of it trying, it may free itself up. And I can always manually shut the compressor off with my switch, if I encounter super low vent temps.

            One thing for sure, i do not like the rapid on/off that it is showing me now at low temps. That can't be good for the clutch.

            But if I leave it screwed in to the accumulator with no wires attached to it, that may just allow it to heal itself. Of course I want it to be working properly when it will be needed more than it is presently.

            It would be warrantable, but I figure the replacement may be in the same condition.

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            • #7
              Originally posted by Cornbinder89 View Post
              I think he has that and a pilot light, he said he added that when he towed a lot with the Blazer
              You are correct. So I can control the clutch manually.

              Comment


              • #8
                Originally posted by huntindog View Post

                You are correct. It originally had a temperture probe into the evaporator. Those did not seem to be all that reliable, and now seem to be unavailable. So I installed the clutch cycling switch instead into the accumulator. Like I said, it was new along with everything else about 6 weeks ago. But it never worked.

                In am figuring that it is trying to start working now. Probably been sitting on the shelf for years and got stuck. (R12 switch)Since under my present conditions, it really isn't critical, I came up with the jumping it idea. Perhaps with some more of it trying, it may free itself up. And I can always manually shut the compressor off with my switch, if I encounter super low vent temps.

                One thing for sure, i do not like the rapid on/off that it is showing me now at low temps. That can't be good for the clutch.

                But if I leave it screwed in to the accumulator with no wires attached to it, that may just allow it to heal itself. Of course I want it to be working properly when it will be needed more than it is presently.

                It would be warrantable, but I figure the replacement may be in the same condition.
                ! I missed that comment somewhere! Seriously I didn't think any were non CCOT only set ups. Accumulator mounted switch with the low port on the same unit.

                If somehow this is not close to OE intentions not sure what to say now. It could drop low pressure but don't understand how if the two ideas were fighting with each other would behave as I wouldn't do that unless somehow no choice.

                Long time ago and didn't think "Chevy" ever used a "thermistor" is I think was it's called sensing temp not pressure - Cadillacs did I think some Buicks used a fuse but blown was blown you got another if not power to clutch??

                Not sure but temps you get are good. The rapid cycling can't be good for it if too often.

                I have to plead "IDK" what you can get for this for funky parts if so and easily?


                Tom
                MetroWest, Boston

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                • #9
                  From what I can remember from back then, they had a VIR (valves in receiver) which has a large accumulator looking thing, It took a replaceable desiccant "bag" with the valves in the removable top portion. A cycling pressure switch I don't think would work with that system. There are a million temp switches with a probe that can be placed in the fins. There are both fixed and adjustable types. Click image for larger version

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                  • #10
                    As far as thermostatic switches Heavyer GM's use a MEI 1331 which is a 24" capillary tube switch fixed 34-38 deg or about a 5 deg off to on temp.

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                    • #11
                      Click image for larger version

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                      • #12
                        Originally posted by Cornbinder89 View Post
                        From what I can remember from back then, they had a VIR (valves in receiver) which has a large accumulator looking thing, It took a replaceable desiccant "bag" with the valves in the removable top portion. A cycling pressure switch I don't think would work with that system. There are a million temp switches with a probe that can be placed in the fins. There are both fixed and adjustable types. Click image for larger version

Name:	GM VIR.png
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ID:	254
                        That I do not have.

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                        • #13
                          Originally posted by Cornbinder89 View Post
                          Click image for larger version

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                          That looks similar to how it was.

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                          • #14
                            Click image for larger version

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ID:	261 Does it have a pilot operated Absolute valve?

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                            • #15
                              No. It is a standard CCOT affair.

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