AC Clutch fuse blowing HELP!

[Duster]

OK, so after a lot of digging around I found that my AC clutch will blow the fuse. If I put another in and try again it blew immediately. After some time passed it would run a bit get cold, then blow.

I took it to the shop, explained the issue, and they said maybe goo in the line filter and what they would do to fix. Dummy who actually worked on it figured out the fuse blew. Didn't really get the job done because it didn't run long enough. The diagnosis was replace everything. Just kinda made me mad.

I took it elsewhere and it was suggested to replace the line because the filter wasn't replaceable. A friend of mine does HVAC so I had him help follow up that diagnosis. That line was pretty restricted. There were no signs of metal shavings or anything. So he also said replace line.

Well, I replaced the line and all was good. Ran a long time as I was recharging the system just to see for sure it worked. If so, I'd have it evacuated and done perfect to spec.

As I say, it ran a long time and got nice and cold while recharging. I was thinking it should have taken the whole 18 oz can I had. But didn't seem to yet. I disconnected to see if I could tell how much more was left in the can to put it. Soon as I did the fuse blew again.

I am very stumped. The clutch cycled on and off many times with no issues. All seemed good. Have I just clogged a new line with the goo in the compressor? The oil looked kinda yellow like at some point dye was ran in it and that mixed in the oil making it snotty.

Or do I have a dang clutch issue? It's honestly doing the same as before. If I put another fuse in tomorrow it will probably run several minutes again and blow again.

I really need help here cause I dunno.

Maybe someone else has had the same issue and fixed it. I've read a few instances where people replaced the whole system and this still happened so I am not way gung ho to just replace it all.

 

[Duster]

Gosh, really? Nobody else has ever had this issue of blowing this fuse?

If not... has anyone ever checked a clutch with a multimeter or checked air gap? Can I (without special tools) take it apart somewhat to have a look, clean it up, etc?

I'm really leaning towards this being to do with work load and heat buildup related on the clutch parts now. It seems I can turn the compressor and slowly circulate the system.

When it's not blowing a fuse it works absolutely fine for a while.

 

[Billwill]

Gosh, really? Nobody else has ever had this issue of blowing this fuse?

If not... has anyone ever checked a clutch with a multimeter or checked air gap? Can I (without special tools) take it apart somewhat to have a look, clean it up, etc?

I'm really leaning towards this being to do with work load and heat buildup related on the clutch parts now. It seems I can turn the compressor and slowly circulate the system.

When it's not blowing a fuse it works absolutely fine for a while.

First make sure that the single wire going to the clutch is not chaffing to chassis somewhere..this carries the +12 volts from the Clutch Relay under the hood...the other side of the clutch relay picks up ground from the mounting of the compressor housing to the engine.

The clutch itself can be replaced without discharging the refrigerant..maybe the bearing it runs on or the compressor bearings are shot!

You can download the KJ Service Manual for your year KJ here...if you have a 2004 model then download the 2003 Service Manual. The Theory of operation section will explain how the AC system works and how to replace the clutch itself and set the Air-gap. The Service Manual includes the Wiring Diagram...check that the correct fuse rating for your KJ is being used

http://www.colorado4wheel.com/manuals/Jeep/KJ

If you need to replace the Compressor itself you will see that the Service manual advises you to replace several other components at the same time as debris can block the Evaporator or other components.

 

[Duster]

Thanks for the info.

It's a 2007 model.

I will recheck the wiring. I have seen about everything but this from an electric clutch. I've seen them literally melt a fuse to dripping from current draw from air gap. I've seen them be fine but stop engaging due to wear. Seen some you could tap with a hammer and get working a little while. But never this.

It seems totally fine when it works. So yeah gotta look at and test wires again. Need to figure out how to check the clutch too with a multimeter. Seems like it could have an electrical problem. I'd like to partially disassemble to see if there is some underhood grime in there causing an issue maybe. Heck maybe just the electrical starts shorting out after it gets heated up.

As far as the AC I think it is fine now. We took it all apart and cleaned everything but inside the compressor. There was nothing indicating any failures. Just to me not knowing what the oil should look like, it seemed snotty to me.

The line with the filter was indeed restricted. Not totally clogged but well restricted. So I replaced that whole line. Afterwards and after blowing fuses friday, yesterday I could spin the compressor and circulate the system by hand. So I'm thinking the prior restriction might have hurt the clutch already.

 

[Duster]

Anyone know what the specs should be when testing the AC clutch with a multimeter?

I'm guessing the coil should have resistance between a certain ohm range when tested. When I test if in range I should probably run it and blow a fuse, then immediately recheck to be sure?

It's very hard to find any info on this and I guess I am either the only unlucky person to experience this issue? Or is there a more popular forum Liberty owners chat on and I am just asking in the wrong place?

 

[Duster]

So as my bad luck continues, my clothes dryer also went on the fritz. In the process of checking that out something dawned on me, so here is what I did.

I unplugged the compressor and installed a new fuse for a quick simple way of testing for wiring faults.

While disconnected and thinking about my clothes dryer issues, I didn't know what ohm values I should get from testing the clutch. So I thought about the diode in the dryer and decided to check continuity both ways on the clutch. Turns out it beeps both ways.

I was thinking some clutches have diodes and it shouldn't have continuity both ways?

 

[Billwill]

So as my bad luck continues, my clothes dryer also went on the fritz. In the process of checking that out something dawned on me, so here is what I did.

I unplugged the compressor and installed a new fuse for a quick simple way of testing for wiring faults.

While disconnected and thinking about my clothes dryer issues, I didn't know what ohm values I should get from testing the clutch. So I thought about the diode in the dryer and decided to check continuity both ways on the clutch. Turns out it beeps both ways.

I was thinking some clutches have diodes and it shouldn't have continuity both ways?

The circuit diagram for the AC clutch shows a built-in Diode going across the clutch coil. This diode is a TVS (Transient Voltage Suppression) diode which basically stops Reverse EMF going back into the circuit when the clutch coil gets powered dropped to it.

Basically an old electrical system on a vehicle that used a distributor with points and a seperate coil would have the points closed to charge up the low voltage side of the coil...when the points open the high side of the coil kicks back a high voltage to ground causing a spark.

A lot of relays used in electronics either have a diode fitted inside it or in its external circuit going across the relay coil. This diode is fitted in the reverse direction to the normal current flow ie. the cathode will face the positive feed. When +12 volts is fed to a 12 volt relay for instance...the voltage flows directly through the relay coil and energizes the relay...the diode ignores this positive voltage because it has the cathode facing the positive side so it cannot conduct. When the voltage is disconnected from the relay...the coil "kicks back" the power stored inside it and the current flows backwards to its original source. So the idea of the diode across the coil is to direct the current back through the coil to dissipate to ground instead of causing arcing across whatever switch/relay contact energized the coil....this is a brief low-current that will not energize the relay again.

I actually do not know why these diodes are not used as standard throughout the Jeeps wiring....stops switch/relay contacts from arcing and thereby burning out.

The Clutch coil however is a large coil carrying a lot of current so you will expect a large amount of back EMF to cause arcing across the AC Clutch Relay contacts so this is why you have this fitted. A TVS diode is used rather than a standard diode because of the high current flow being carried to ground.

So yes there is a diode fitted across the clutch coil...not in series but in parrallel to carry the back EMF to ground when the clutch is switched off.

To measure if this is still working ie. is not allowing the current to flow back through the relay contacts and the 20 Amp fuse is difficult.

I have two Digital Fluke Multi-meters...the best in the bussiness...which have settings for testing diodes, transistors etc. Even with all my years of experience I find this method of testing diodes or transistors to be pretty useless as these devices are currrent dependant and the low current put out by the Digital meter test probes is useless. I keep an old Analog meter for testing these devices. You will get your meter beeping in both directions as you are measuring through the clutch coil itself...there is no diode in series!

The fact that this Diode is packed in with the clutch coil makes it even more difficult to test....most vehicles I have worked on have the AC Clutch diode mounted externally.

So you could try to obtain a high current/high voltage diode and connect it in series with the clutch coil...stripe on the diode ie. cathode facing towards the coil...this would stop back EMF going back through the fuse but there would be a fair voltage drop across the diode or put the diode across the coil as the TVS diode is at present..in this case the stripe on the diode faces the incoming +12 volts.

So in summary....it is possible that a high current surge is flowing back through the fuse due to the current TVS diode having failed.

Only way to test this really is to pick up a used clutch coil from a Breaker yard or buy a new one and try it out.

I still believe that you more likely have an intermittant short to chassis of the wiring going to the clutch. You could pull out the fuse and AC Relay, disconnect the connector to the clutch....provide a direct feed of +12 volts from the battery via an inline fuse and manual switch direct to the clutch and see if that works for a while but if you are low on refrigerant you will damage the compressor! Or you could cut off the wire going from the relay pin 30 to fuse 21 on both sides and run a new wire and likewise cut off the wire coming off the relay pin 87 and going to the clutch both sides and run a new wire.

If you do not have the wiring diagrams...download the KJ Service Manual for your year KJ here...includes wiring diagrams:

http://www.colorado4wheel.com/manuals/Jeep/KJ

 

[Duster]

OK thanks, that saved me cutting off covering of the wire hunting what I wouldn't ever find.

So replace the clutch or replace everything.

This is a debate for me. The clutch looks easy, one bolt. But I bet I'd need something to hold it still, then it's probably pressed on and I'm not sure how this one would pull off.

Anyone replaced the clutch that knows what the job is all about and what tools are needed?

Can't decide between tackling the clutch or just replacing the system now.

 

[Billwill]

OK thanks, that saved me cutting off covering of the wire hunting what I wouldn't ever find.

So replace the clutch or replace everything.

This is a debate for me. The clutch looks easy, one bolt. But I bet I'd need something to hold it still, then it's probably pressed on and I'm not sure how this one would pull off.

Anyone replaced the clutch that knows what the job is all about and what tools are needed?

Can't decide between tackling the clutch or just replacing the system now.

The Link I have given you above to the KJ Service Manuals...I do not know what year model you have... will tell you how to replace the the clutch itself and put it back together with the correct air gap....sorry but I have just added the link now...thought it was there!

I notice that the 2005 manual lets you locate the Diode inside the harness and replace it!

Or you can stay on this jeepkj forum, go to the "KJ How To section" and search for "AC Clutch"...there are some good hits there!