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Chris (aka- Moose)
Chris (aka- Moose), Mercury Technician
Category: Mercury
Satisfied Customers: 1957
Experience:  16 years experience with Mercury
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Voltage oscillates when engine is running. Does not vary

Customer Question

voltage oscillates when engine is running. Does not vary when engine is off. Oscillation frequency does not vary with engine rpm.
Also, Heater / AC fan stops running when car is accelerating (under load). Fan operates fine under all other conditions.
Related issues?
Submitted: 1 year ago.
Category: Mercury
Expert:  Andrew Martin replied 1 year ago.

Sounds like the alternator is bad. I'd start there. Should have a consistent 13.5 - 14.5 volts when running. If it varies a lot the voltage regulator inside the alternator is probably the issue.

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Customer: replied 1 year ago.
Your answer does not address the Heater / AC fan issue.
Expert:  Andrew Martin replied 1 year ago.

When the voltage is low or changing rapidly it makes the electronics not able to run. The battery is just to start the vehicle, the alternator runs everything.