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| '75 Duster w A/C keeps blowing #5 fuse. https://slantsix.org/forum/viewtopic.php?t=41416 |
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| Author: | Oldspowered [ Fri Aug 13, 2010 6:23 am ] |
| Post subject: | '75 Duster w A/C keeps blowing #5 fuse. |
My slant-6 '75 Duster has factory A/C. The A/C will blow cold for about 10 minutes then the #5 fuse blows and the power to the compressor clutch is cut. Everything else in the car works except the A/C clutch. I can run a jumper to the A/C clutch and it works fine. I have poured over the diagrams for a '75 Dart here: http://www.mymopar.com/downloads/1975/75DartA.jpg http://www.mymopar.com/downloads/1975/75DartB.jpg but nothing lists the A/C circuit. From what I can trace if the #5 fuse blows I should lose a few lights, but I don't. The fuse is a 20-amp so I know there is some serious power going somewhere, but surely it shouldn't be going to just the A/C compressor clutch. I'm tempted to run a relay setup to isolate the power to the A/C clutch and see what happens (using a 20-amp fuse in the relay power circuit). I have searched all over and can't find anything that diagrams out the A/C circuit. I am hoping someone here knows it a little better than I do. |
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| Author: | Charrlie_S [ Fri Aug 13, 2010 7:17 am ] |
| Post subject: | |
Run a jumper wire to the clutch, thru an ammeter, and check the current draw, while it is running. I don't remember the spec, off the top of my head, but it should be less then 10 amps max. The current will increase as the clutch gets warmer, but stay under 10, amps. I would be willing to bet the clutch coil is partially shorted.. If that checks good, there should be no other draw on the fuse for the clutch, so there would have to be a short in the wiring. The power goes from the fuse through the PB switch, to the "anti-freeze" (fixed t-stat) sw, to the pressure sw on the drier, to the clutch. It should be an 18ga green wire from the fuse to the PB sw. From the PB sw the rest of the way is an 18 ga dark blue wire. |
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| Author: | Oldspowered [ Fri Aug 13, 2010 11:05 am ] |
| Post subject: | |
Quote: Run a jumper wire to the clutch, thru an ammeter, and check the current draw, while it is running. I don't remember the spec, off the top of my head, but it should be less then 10 amps max. The current will increase as the clutch gets warmer, but stay under 10, amps. I would be willing to bet the clutch coil is partially shorted.. If that checks good, there should be no other draw on the fuse for the clutch, so there would have to be a short in the wiring. The power goes from the fuse through the PB switch, to the "anti-freeze" (fixed t-stat) sw, to the pressure sw on the drier, to the clutch. It should be an 18ga green wire from the fuse to the PB sw. From the PB sw the rest of the way is an 18 ga dark blue wire.
I'll give this a try tomorrow morning. I think I have an ammeter sitting in a box at home.If the clutch is drawing more than 20 amp on the meter but not more than 30 I might just do the relay setup like I mentioned before. Apparently I can only get a RV2 clutch for V8 models, no idea what the difference would be for the slant-6 version (the only one I can find is this one: Part #48833, w/ RV2 Compressor; Reman; 5-3/8" O.D. Clutch). |
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| Author: | wjajr [ Fri Aug 13, 2010 12:53 pm ] |
| Post subject: | |
Oldspowered: Quote: If the clutch is drawing more than 20 amp on the meter but not more than 30 I might just do the relay setup like I mentioned before.
Your inviting the fire gods to descend if you over fuse the conductors & windings that opperete the clutch. Instead of a fuse blowing, the device and or conductors & equipment serving it will have a melt down. Just test & find the offending part, and replace it to reduce possible collateral damage. |
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| Author: | emsvitil [ Fri Aug 13, 2010 12:57 pm ] |
| Post subject: | |
Clutch coil resistance (cold) is normally in the 3-4 ohm range. So the amp draw will be somewhere around 4-5 amps. Clutch coil internally shorting is a possibility. It could be fine cold, then as it heats up from use, the wires expand from heat and THEN short out........... |
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| Author: | Charrlie_S [ Fri Aug 13, 2010 4:27 pm ] |
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What Ems said. Those numbers sound correct. If it turns out you do have a bad clutch coil, send me a PM. I might have one in stock. |
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| Author: | Oldspowered [ Mon Aug 16, 2010 7:34 am ] |
| Post subject: | |
Ok, Saturday morning I hooked up a ammeter to the clutch coil. From what I could tell on the gauge it was pulling no more than 4-5 amps. I ended up taking apart the A/C clutch wiring harness, cleaning the connectors and re-taping the ends where it looks like some hack mechanic stripped the connectors instead of back-probing the junction. I also pulled apart the large connector on the passenger side, pulled out the spade connectors, cleaned them and put them back. I found two wire bare spots but could not figure out where they could be touching metal. I let the car idle with the A/C w.f.o for a good 20 minutes while I did yard work. The #5 fuse was hot but never blew. We'll see what it does on the way home from work tonight. It is nice to know the clutch coil isn't dead, that is a project I do NOT want to try. |
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| Author: | wjajr [ Mon Aug 16, 2010 1:35 pm ] |
| Post subject: | |
You may want to just run new conductors, and fit new brass connectors in that circuit. It is possible that there is corrosion that has formed under the insulation, or there is a partial brake of the existing conductor somewhere that you can’t see causing excessive resistance. Often that bulkhead connector is a prime location for corroded connections, and excessive heat build up as well. |
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| Author: | Oldspowered [ Wed Aug 18, 2010 10:50 am ] |
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New wiring for certain components is probably in the future for this car. So far I've been using the A/C all week and no fuse problems. |
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