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I have an 81 caddy with an 84 GTI complete swap from previous owner.

I believe my alternator is on it's last legs, I'm getting 13.5v when running, but as soon as I turn the AC on (causes rad fan to spin up) it drops to 12.5 to 12.8v.

I'm looking at my Bentley, youtube, and threads and it the research seems to say that I DO NOT need to remove my York compressor to get that alternator out, but looking into the engine bay it sure does LOOK like I would need to.

Wondering if anyone has experience with this. Does the alt come out the top?
 

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Bottom if I recall correctly for a York.

If you are measuring the voltage on the meter in the dash, that is about correct range for a working alternator.
The a/c is a hog and the Belt Tension on the alternator is possibly too-loose.

I would first go cleaning or better if they aren't new, REPLACE the Battery to Frame, and Frame to engine grounds.
I would then Verify your readings on the dash gauge with a DVOM on the Battery.

As I said that is about normal as to what I see on my Cabriolet....
As I have my headlights relayed, I don't see as much of a drop with those on.

You should probably also Clean your alternator plugs.

On a side note, do you have a 60A or 90A alternator, and there is a thread on the Cabriolet section on how to boost your output.
http://forums.vwvortex.com/showthrea...for-regulators.

As you tested the voltage at the battery they are about normal for the car.
I do know that the Voltage Gauge in the car is prone to be iffy. I have one that the gauge is 1 volt lower than actual on the battery, and that is with new wires and a new gauge.
 

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I have a 1980 Rabbit with a/c and York compressor on top and 37+ years of dealing with the alternator etc.


If you need to remove the alternator intact, the easiest way to do that is to drain and remove the radiator. Then there will be enough clearance (barely) to remove it. There are 2 nuts and a clip to remove the radiator, rather fast once you resign yourself to that.


You can remove and replace the voltage regulator without disturbing anything else. Sometimes a bad regulator causes these issues.


I understand that VW used several different systems to maintain the idle speed when the a/c compressor would operate. On 1980's, they used a solenoid valve to advance the ignition timing. I think that 1981 used a different system. Suggest you check to see that whatever system you have is functioning properly. If the idle speed is not maintained, the alternator output will drop even if the alternator is good.


In previous years, I was able to disassemble the alternator without removing the radiator or anything else. It was then possible to replace the diodes and then re-assemble the alternator. It is now difficult to find these diodes so I would not suggest you go this route unless you're familiar with electrical circuitry and able to solder and unsolder diodes without damaging them.


You can get a rough idea of the alternator's state by connecting a digital voltmeter across the battery terminals with the engine OFF, the doors closed, and all electrical accessories OFF. Write down the number. Then start engine and turn on headlights and let engine idle, vent blower on low speed. Voltage should be HIGHER than the first number. With a/c on, blower on high speed, engine 1300 rpm or so, voltage should still be higher than the voltage with the engine off.


Good luck.
 
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