I have tracked it down to fuse [#29] that blows every time I push the "snowflake btn".

If I disconnect the terminals on the "low pressure" switch & pushed the btn; the fuse does not blow -- all fans run, relay clicks, etc.. -- so it seems to be an issue down stream of the pressure switch -- toward the compressor/clutch.

Using an ohm meter and trouble shooting light, I find the black wire from the compressor clutch is a sold ground connection. I have looked for any obvious grounding problems following the wires / harness.

According to the wiring diagram, there is also a wire that runs to the DME control box from the compressor/clutch . Not sure what this does, maybe kicks up the idle for the compressor.

Anyway, I am stuck. Any ideas where to go from here? Is this going to be a replacement of the clutch/compressor or the DMS control unit?

thanks, jeff
1987 944 NA

 

I believe Porsche uses Brown for ground.

 

there was a thread about this a few weeks ago. Search "clicking sound under dash" and "AC fuse"

it seems a few of us are all having the same problem, but with different causes.

 

Yea, I just went through this too. I think your problem is the clutch winding. It can be replaced without disconnecting the compressor lines but its a little difficult. First disconnect the compressor except for the pressure lines. Let the nose hang down. Then use a clutch tool to hold the clutch from turning, then remove the 13mm shaft nut and lock washer. Use a second clutch separator tool to pull the clutch pulley. This will expose the winding, remove a large snap ring and it is free. In my case the clutch pulley was bent a little and would touch the winding, and occasionally short and blow the fuse. I don't think you can buy just the winding but have to buy the whole clutch and I think they are priced at something like $90. While you're in there get a good look at the clutch bearing they are durable but do sometimes fail.

Oh almost forgot.... there is a small washer that goes between the clutch and the compressor (along with a square xxxxxxx key). That washer is important as it establishes the air gap. Its a little tricky to re-assemble with the comp still on the car - I had to super-glue the key in place to keep it from dropping out....Bruce

PS Rip is right - Brown is ground the world around. The compressor line is not a ground though.

 

Whats the best way to test all this stuff?

I mean, I've heard the clutch winding, the electrical plugs behind the climate unit, the coils behind the glove box, the power steering pump pressure switch.....etc.

I haven't gotten to far into this yet, but this is my list of things to check so far.

 

Thanks F18, I too suspect the clutch winding. I have called my local 944 part shop, and they want 159 buncks for a used clutch. Where can I find the one for $90? Anyone got one laying around?

Mark, in my case I isolated the circuits to narrow down the problem. I disconnected the terminals on the low pressure switch [located behind the drivers side headlight], put in a good fuse and pushed the a/c snowflake btn that causes the fuse to blow. Since the fuse did not blow, I figure my issue is down stream from the low pressure switch. I confimed this with a test light - the wire from the compressor is grounded somehow.

According to the wiring diagram, there is another wire that comes from the DME to the same compressor connection; so I will again isolate and test to confirm this wire is not ground; which is unlikely.

 

So what does the AC relay control?

I assumed the button was seperated from the compressor by the relay. As in, the button was the fuse, and anything connected to the pump (that required more juice) was on the relay.

So I'm not understanding why the fuse pops when the winding on the compressor is bad. A relay is designed just for this purpose. To seperate high amp things from low amp things. (I haven't looked at my wiring diagrams...like I said, I'm assuming this.)

 

Just when I am ready to buy the $60 clutch on ebay, you add some reasoning to this thread.

For some unknown reason I was stuck "on the hunt" for a grounded wire causing the fuse to blow - figured the black wire to the compressor winding is a positive lead and should not be grounded. Maybe this wire tests as a ground naturally because its a coil winding???

There was a post that described how to test the relay diodes and I found these to be OK; but I am not reliable when it comes to electronics. So my next is to get another relay and see what happens before I go thru the clutch replacement ordeal.

 

Well, I went back to test the wire coming from the A/C relay to the low pressure switch - when I press the snowflake btn, this wire lights up as a positive lead. So I am gong to order the clutch w/ windings.

BTW, I added this nugget from Texaserick; he sells rebuild clutches on eBay for $60.

" ... the coil inside of the clutch has 2 wires: 1 grounded and 1 is for a 12 volt positive feed from a relay that your snowflake button is turning on. A coil is just actually a dead short to ground. Before it does nothing and blows a fuse, it creates an electro-magnet like you made in science class. I would disconnect the wire going to the clutch ( coil ) and then try pushing the snowflake button. If it does not blow a fuse, then 99% of the time you have a shorted coil. It probably is melted from use and the windings are touching the sides of the steel coil housing causing a dead short and blowing a fuse. Try the disconnection first. Sometimes the bearing inside of the clutch pulley spins freely and will melt the coil plastic that holds the windings and causes a short to ground. If you buy my clutch or someone else's, remember to put a couple of drops of 3M weather strip glue on the compressor nose piece before installing the clutch assembly. This will keep the bearing from free spinning and burning up a new clutch assembly. Now, all that I have just said could be a waste of time if your compressor is locked up / burnt up ? You will then need more than just a clutch assembly."

 

let us know how it works

 

Clutch coils "fry, short, melt, etc." because of heat. The heat comes from either: (a) worn pulley bearing, or (b) high side head pressures (too much psi on the high side), (c) lack of refrigerant oil in the system. Any of these situations generate heat. The heat is transmitted through the aluminum nose on the compressor and to the coil (copper winding) which is a very good heat sink and absorbs the heat. When the temp gets too high the coating on the coil wire melts and you get a short. Signs of this are melted or cracked encapsulation, fire, smoke, open's or shorts. Heat can also degrade the pulley bearing grease and shorten the life of the bearing.

Sometimes you can get "lucky" and replace the coil, however most times you will simply end up frying another coil.

Worth the 60-$90 gamble? Maybe... its just time and money.

 

Replaced the compressor clutch and all is just fine. Could not tell what was causing the short; but who cares I have A/C again.

Bought a rebuilt clutch on ebay for $60 delivered from texaserick and had the local Porsche shop install for $208. At this rate, hope it lasts for awhile.

Thanks everyone.