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Experts Inside Please - Blowing A/C Compressor Clutches

EverydayDiesel on Thu May 22, 2008 4:18 PM User is offline

Year: 2001
Make: Dodge
Model: Ram Diesel
Engine Size: I6
Refrigerant Type: R134
Ambient Temp: 85
Pressure Low: 75
Pressure High: 75
Country of Origin: United States

A little background first. Its a 2001 dodge diesel and I have replaced the compressor, liquid line (with orifice tube), drier, and condenser. I have snap-on manifold gauges and a 5cfm robin air pump. I flushed out the evaporator with a/c cleaning chemicals before doing any of the work.

First thing, after installing all the new pieces, I drew down the system for 45 minutes and let the system hold the same -29 psi for an additional 45 minutes. No leaks. I go to add the first can of refrigerant to the low side of the system and turn the a/c on to get the other 1/4 of a can out. The fuse blows and there is no resistance on the coil. I get a new pump from the dealership.

I hook the second pump up and draw down the system, add refrigerant, swapped the relay with a new one and replaced the fuse. I start the a/c and the 10amp a/c clutch relay fuse blew and the coil now reads a dead short. I replaced the fuse but of course it blew because the coil reads 0.3 ohms of resistance...basically a dead short. I replace the fuse again with the connector disconnected from the compressor and ran the truck. This showed me that the wires going to the compressor is not grounding out anywhere.

The third new compressor I get from dodge reads 3.5 ohms across the coil. I replace the pump, draw down the system and add refrigerant. I have 14v on the truck connector side before plugging in the pump. I plug in the connector to the pump and turn the a/c on. The fuse blows and now the coil reads 0.3 ohms.

Does anyone know why I keep blowing coils on these brand new compressors?

Edited: Thu May 22, 2008 at 4:41 PM by EverydayDiesel

mk378 on Thu May 22, 2008 4:37 PM User is offline

Maybe there's a diode inside the coil and the polarity is wrong? This will instantly blow either the diode first or the fuse first, diodes almost always fail shorted. Does it blow instantly or did the compressor operate for at least a short time?

EverydayDiesel on Thu May 22, 2008 4:49 PM User is offline

Compressor never spins...fuse blows instantly. Where is the diode at? inside or outside the pump?

Service manual says +12 volts on the black wire and ground to the white/black wire. that exactly what its getting.

Its a connector so it just plugs right in, theres a guide so theres no way to plug it in the wrong way.....unless dodge changed the wiring...would they do that????

Edited: Thu May 22, 2008 at 4:51 PM by EverydayDiesel

mk378 on Thu May 22, 2008 4:54 PM User is offline

You may be getting the wrong part. Do you still have your original compressor, which I assume has a problem other than the clutch? Maybe you can mix and match the coil. Do they show the pin-out of the plug? Could have the wires in the plug wrong.

EverydayDiesel on Thu May 22, 2008 5:08 PM User is offline

is it possible to repair this clutch? is it just the diode that is bad?

Im thinking if i can replace the diode then I can swap the wires and see if it works. its worth a shot

mk378 on Thu May 22, 2008 5:12 PM User is offline

I think the diode will be molded into the coil plastic.

Most compressors it's possible to take the clutch plate, pulley, and coil off while it's still mounted to the engine without disconnecting the refrigerant lines.

Next time you're at the dealer find a truck like yours and pop the hood to see which way the wires are.

ice-n-tropics on Thu May 22, 2008 5:25 PM User is offline

Your trying to feed the 2 wire clutch with the polarity reversed. Maybe somebody reversed the vehicle wires inside the connection plug.
After reversing the vehicle harness, you can obtain a 1000 (600 volt second choice) volt Motorola diode to replace the blown diode.
There is a slight risk of frying some onboard electronics if the diode is omitted. When the clutch is disengaged, the magnetic field energizes the wires with a negative voltage spike up to 600 volts. The diode blocks the spike from entering the vehicle wire harness and forces the current to go round and round the coil windings until the energy is dissipated as heat.
Cordially,
Old IV guy

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Isentropic Efficiency=Ratio of Theoretical Compression Energy/Actual Energy.
AMAZON.com: How To Air Condition Your Hot Rod

Edited: Thu May 22, 2008 at 5:26 PM by ice-n-tropics

EverydayDiesel on Thu May 22, 2008 5:51 PM User is offline

I called the dodge dealership to confirm that pin 1 (black) needs +12v going to it (which it does). They also told me that pin 2 (white/black) needs ground which it has.

Unless dodge decided that they were going to swap the wires different from what the service manual says. (inside the pump)

Is it possible that the factory did this??? It seems ridiculous.

Do I have to take the pump apart to replace the diode? Im reluctant to do this since the pump is brand new and under warranty.



It is hooked up correctly now. Is

Edited: Thu May 22, 2008 at 6:16 PM by EverydayDiesel

EverydayDiesel on Thu May 22, 2008 7:04 PM User is offline

I took my old pump and hooked it up EXACTLY like the old one.

black to black and white/black to white/black

the old pump engaged like it is suppose to.

Chick on Thu May 22, 2008 7:08 PM User is offlineView users profile

The diode will be in the harness, not the compressor. Usually moulded in the harness not to far from the compressor and you can feel it being thicker. Chysler did use a "square" ceramic looking diode on a lot of there 10PA17 compressors, not sure on yours. On those it was mounted right on the compressor..You may need a wiring diagram to locate it, but it's very unusual to be blowing coils, especially right from the start...

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Chick
Email: Chick

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Freedoms just another word for nothing left to lose

EverydayDiesel on Thu May 22, 2008 7:17 PM User is offline

the thing that gets me is that if you hook up a diode backwards it resists (or blocks) the voltage. It shouldnt blow.
What would make more sence is if the factory shipped the wrong size diodes or if there was something wrong with the coils being weak.

Otherwise how do you explain hooking up my old pump and it works...no fuses blown...no coil short and the coil locks up like its suppose to.
Its a connector with a guide so you can only plug it in one direction.

Chick on Thu May 22, 2008 7:24 PM User is offlineView users profile

It's a little tough not being able to put our hands on it so to speak, but it sounds like a dead short. They run without diodes, and the risk of blowing your electronics isn't that great, "but it is there"... As for the size, I doubt they have many sizes, diodes are one way currant. You have to go over your harness very carefully and look for a wire touching or something.. Sending 12volts into the coil is "normal", thats how they work. But blowing the fuse right away means a short. I guess it's possile they got a bad run of compressor coils, but it's highly unlikely.. Maybe use you old coil and try that.. You can't put more volts into it than the car puts out..Has to be a wire touching ground.

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Chick
Email: Chick

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Freedoms just another word for nothing left to lose

Chick on Thu May 22, 2008 10:34 PM User is offlineView users profile

One other thing you can try..Get a new plug connector from a junk yard, strip the wires back, and run 12v to one wire ground to the other. If the clutch engages, you know the problem is in your harness (add a fuse to the hot wire of course) if the fuse doesn't blow, you know the fault is not with the coils, I would seriously take a good look at your plug..A wire may be touching inside when you press it in..Just a thought...

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Chick
Email: Chick

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Freedoms just another word for nothing left to lose

EverydayDiesel on Thu May 22, 2008 11:41 PM User is offline

Quote
Originally posted by: Chick
It's a little tough not being able to put our hands on it so to speak, but it sounds like a dead short. They run without diodes, and the risk of blowing your electronics isn't that great, "but it is there"... As for the size, I doubt they have many sizes, diodes are one way currant. You have to go over your harness very carefully and look for a wire touching or something.. Sending 12volts into the coil is "normal", thats how they work. But blowing the fuse right away means a short. I guess it's possile they got a bad run of compressor coils, but it's highly unlikely.. Maybe use you old coil and try that.. You can't put more volts into it than the car puts out..Has to be a wire touching ground.

well if i unplug the compressor...with the harness completely disconnected, I replace the fuse and turn the a/c on....the fuse never blows
which means the wire going to the compressor is not shorting out anywhere, if it was touching metal it would blow the fuse if the compressor was hooked up or not.

The second i plug in the compressor and turn the a/c on the fuse pops which means its something with the compressor (or all three of them). I tested the outer casting (metal part of the compressor) against each of the terminals thinking it was shorted out but it was not.

The dodge dealership says that its a bidirectional diode...which means it shouldnt matter which direction you hook it up even though I am hooking it up according to the factory service manual.

The meter shows i have ground, but would a bad ground cause this to happen? (in bad i mean not making a good connection)



Edited: Thu May 22, 2008 at 11:46 PM by EverydayDiesel

Chick on Fri May 23, 2008 6:16 AM User is offlineView users profile

check the plug on your harness..Change it if necessary..Unless someone can come up with another solution, it's a dead short to me. This is not a diode problem, not to say you didn't blow yours out..Do you have your old coil? plug it into your harness and see if the fuses blow. If they don't, wiggle the plug around and see if it blows, I think it's in the plug..Sure wish i could see it.. If you're getting new compressors, what are the odds all have shorted out coils??? And remember, the coil works by putting all the voltage into it..12v to ground is what is popping your fuses..

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Chick
Email: Chick

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Freedoms just another word for nothing left to lose

NickD on Fri May 23, 2008 8:35 AM User is offline

It's nice to have the test equipment to check these things like a current limited power supply that won't blow even if feeding a dead short circuit, fuse are expensive. Wouldn't be a bit surprised of one of the coil feed wires is crimped to a ground, hard to conceive you got a shorted coil, but whatever the problem, shouldn't be that way, even an ohmmeter is cheaper to use than a box full of fuses. Take it back.

The diode is a flyback diode to prevent high voltage spikes from destroying other components, is paralleled to the coil with the anode connected to the negative ground and the cathode to the positive side or reversed biased. When using a current limited power supply, if the voltage is connected in reverse, but increasing the allowable current, the voltage will only increase to about 0.8 volts, it will never get much higher than this, if you let the current increase beyond the capacity of the diode, it will overheat and eventually blow.

Electron current flows from negative to positive so the ground side of the coil will be negative the high side positive, when the positive side is opened, say by a relay contact opening, the magnetic field around the coil collapses, and induces a voltage of the opposite polarity that caused it, but now the coil is becoming the source and not the load.

With the top of the coil now negative, and the bottom of the coil positive, the direction of the current does not change, still flowing from ground to the high side, but since the polarity is now reverse, that diode is forward biased and provides a decay path that limits the collapse time of the field vastly decreasing it's rate of change. So when view with a scope, the top coil side never gets greater than the applied voltage or around 12 volts, you just see this voltage decay at an exponential rate. Typical diodes only see a peak current of 4 amperes on decay that only last for a few microseconds, so a diode with an average current flow like one ampere like a 1N4002 is more than adequate.

Regarding the reverse breakdown voltage, that more depends on the greatest voltage seen on the vehicle's electrical system that is limited to 40 volts maximum for short duration spikes, Chryslers are high where GM clamps this voltage to 22 volts maximum, so even a 200 volt reverse breakdown diode would be fine.

Without this diode, the field would collapse very quickly generating a very high voltage that would arc the relay contacts or blow a solid state feed.

Just some basics for those interested in this stuff.

I like pretesting this electronic/electrical stuff as much as possible on my bench before installing it, it still looks new when I bring it back and have found lot's of bad new stuff off the shelve, and in the case of a compressor, it's a lot of work to install it only to find out you have problems.

Ever see that big sign, no returns on electrical components, well I have returned them and if they want a snow job as to why, can give it, but in short, you sold me a POS. No one compensates me for my labor and normally have to give a fight to exchange a part or get my money back.

jglanham on Fri May 23, 2008 2:54 PM User is offline



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johnl

jglanham on Fri May 23, 2008 3:40 PM User is offline

Just had to throw my 2 cents worth in here. It appears to me that the third coil that measured 3.5 ohms was a good coil. However, an ohmmeter will not tell you if a diode is in the circuit with such a low resistance. If there was a diode across the coil and installed incorrectly, it would short and blow the fuse, which would give a low reading on your ohmmeter, indicating the short. The coil itself is probably still good. I would try to get the compressor replaced if the dealer will allow it. When you get the new one, try this simple procedure to test whether the diode is present and/or installed correctly. Obtain a 12 volt automotive taillight bulb (bayonet style). Carefully solder a test lead onto the outer shell and another one to base connection that goes to the filament that is used for the brake light. Obtain some clip leads and connect a lead to the positive terminal of a 12 volt battery. Connect the other end to one lead of the bulb. Connect the other lead of the bulb to the black lead of the clutch coil. Connect one end of another clip lead to the negative terminal of the battery and the other end to the white/black wire of the clutch coil. Observe the brightness of the bulb. Reverse the leads on the clutch coil. Observe the brightness of the bulb. If there is no difference in brightness, there is not a diode in the circuit. If one way is dim and the other is bright, there is a diode in the circuit. The bulb will be dim when it is connected correctly. I suspect you will find the diode is backwards in the coil. And yes, the whole production run could be that way, especially if the units are never tested before they leave the factory! That's assuming that they are giving you the correct part. Hope this helps.


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johnl

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