It seems the voltage regulator blows when the AC or heater is turned on. I've now replaced the alternator 3 times (re-built each time). In this latest alternator I've put in a new Bosch voltage regulator. I also replaced the battery. Also the starter was replaced about 6 months ago.

I know it is blown because the battery is not charging, and the voltage at the battery, when the car is running is 13.8V. I replaced the regulator, and when the car is running, the voltage at the battery now is 14.1-14.3 volts.

There is no serpentine belt in this car.

Any ideas?

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1989 420 SEL