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Discussion Starter #1
Hi I started a thread earlier in the year re: this question but got a bit squirrled and didnt get very far so I did a bit more testing last night, we have no cold air and the clutch stopped cycling, there is zero volts going to the clutch with motor running, a/c on, if I jump the connector at the evaporator?, (round cyl by the firewall passenger side) on the pressure switch I can get 12v at the plug going to the clutch but it still wont cylcel I checked the ground side of the two pin harness for continuity to ground, its good, I checked each side of the clutch plug from the clutch for dead short to ground, its good, with the engine off I can free spin the clutch by hand so not seized, I am thinking two problems...low pressure in the system causing the pressure switch not to trigger the clutch hence no power at the clutch and a open circuit in the clutch coil causing it not to spin, also just a note the a/c stopped pumping cold prior to the clutch not engauging by maybe two months or so, on a positve note fuel mileage increased after the clutch stopped, lol, any thoughts, its HOT up here!
 

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Well, if you jumpered the low-pressure switch and the clutch plug now has 12V and didn't without the jumper, then that suggests low system pressure. However, if you now have 12V at the clutch plug by jumpering, and the clutch still won't engage, then there is another issue.

If you have power, then the clutch fuse is not blown. If the clutch coil were shorted, it would blow a fuse. If it were open, that would explain why the clutch won't engage even with power applied. You say you have continuity on the clutch coil - how many ohms?

Do you have access to a pressure gauge, so you can check high and/or low side pressure? Is this still R12 or converted to R134a?
 

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Discussion Starter #3
Hi thanks, I didnt check continuity at the plug to the clutch I ment to but forgot, I will tonight or tomorrow, what should it be?, I dont have proper gauges just an after market kit with a gauge attatched, would that work?, and I THINK I am r134 I will have to check
 

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I don't have an exact number, but somewhere between about 3 and 8 ohms will be right. Not critical, just shouldn't be either open or shorted.

If you were converted to R134a, there are adapters screwed on over the low and high pressure valves, that are quick-connect fittings, instead of the threaded valves that are original and underneath the adapter. If you remove the dust caps and can see threads just the same as tire valves, it's still R12.

An aftermarket fill kit would have a low-pressure gauge. If the system is full, with engine off I'd expect at least 100 psi.
 

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Discussion Starter #6
hi Bob well I finally got back to this, there is 5.5 ohms between the two terminals going to the clutch nothing between either terminal to ground but I still think there is an "open" here as mentioned earlier when 12v is applied to the clutch there is nothing, I checked the availability of the clutch with Napa they say compressure only, no clutch, I will check another supplier tomorrow but I am thinking maybe the auto wrecker for the entire compressure, it is simple to change, right at the front, top of the engine, five bolts, one set of lines on the manifold holding them to the unit and one plug in, should take 15min, I beleive the r134 gas has already expired so I will just un-bolt the lines, two new orings, and a aftermarket fill kit with gauge and should be good! hopefully the auto wrecker unit will be cheap, I have a good connection at one of the local yards
 

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An change the drier....
Dont forget to vacum it also.
 

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Yes, drawing a vacuum for an hour with a pump (and having it hold vacuum) is mandatory.
 

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The clutch doesn't fail often. It's more common for the compressor guts to wear out.

Before replacing the compressor, with engine off try jumping 12V to the clutch pins and see if the clutch moves. It should retract to the body of the compressor. If it does, the clutch is good. In that case, I'd look for a wiring issue.

Yes, a standard vacuum pump will do. Harbor Freight has a 2.5 CFM unit for $100 that I use.
 

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Discussion Starter #11
well Bob thats basicly what I did when I jumped the pressure switch I undid the plug at the clutch then jumperd the pressure switch then used a volt meter to confirm 12v at the plug where it connected to the clutch then when I was sure there was 12v plugged it back together it should have moved then but didnt, so thats why I think the clutch is toast, oh, also I confirmed ground at the same plug
 

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mopar56 said:
well Bob thats basicly what I did when I jumped the pressure switch I undid the plug at the clutch then jumperd the pressure switch then used a volt meter to confirm 12v at the plug where it connected to the clutch then when I was sure there was 12v plugged it back together it should have moved then but didnt, so thats why I think the clutch is toast, oh, also I confirmed ground at the same plug
Technically you didn't do the same thing. You verified 12V at the battery side of the clutch plug. You verified that the winding resistance is OK on the clutch side of the plug. But if there is a connection problem when the two are mated, then the clutch may not activate. For instance, my compressor in one car would not turn on even when plugged in, and there was power at the plug (battery side). I plugged it in again, drove about 10 more miles before it suddenly turned on. It was a connector issue.

And in many vehicles, there are integral back-to-back diodes inside the plugs, to prevent inductive kickback to the relay. If one of those diodes is shorted, it can prevent the compressor from kicking on.

I would turn on the A/C and probe through the insulation of the clutch wire, between the clutch and the plug, to be sure that 12V is going to the winding itself. Just before spending a few hundred dollars. The clutch could still be bad with a good winding, but I'd do more diagnostics first.
 

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Discussion Starter #14
ok point taken on the test although I seem to remember back probing the connector on the clutch side with a pin and volt meter but I could have lost some voltage there, this was a pretty basic connecter I dont think any diodes here, I will supply 12 direct for the time it would take and re-confirm voltage.
Imperial how do I identify a Sanden? is it marked or labled?, as for r134 in Canada I believe all vehicles had to have r134 by 1995 so the system we have is factory r134 as the truck is a 1999
 

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Again, jumping 12V direct to the clutch side of the connector with engine off should result in the clutch being pulled in. If not, it's bad.
 

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Sorry, it was difficult to determine the year. I was thinking that it was a 1990. A 1999 would certainly be R-134a.
The circuits didn't change that much through the years. A diode may be across the A/C compressor clutch relay points to mitigate the inductive kickback from clutch disengagement. It shows it across the clutch coil here:
78615741.gif
 
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