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2014 Forester 6-Speed Stick
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Discussion Starter #1
Right about the time my engine was getting replaced for the second time (since I have owned it) on my 2014 base model 2.5i, the Air Conditioning started just cutting out on it's own. Just stuck in traffic or driving on the highway on 85 degree days and the AC would shut down. I could usually get it to come back on by turning the AC off and back on again several times, but not always.

Fast forward about 2000 miles, the car's third engine is in, weather has been nice and I have been riding my motorcycle. I get back into the car for a family outing on a nice, holiday weekend and the battery light comes on and won't go off. I'm 200 miles from home, with no tools, on the Sunday of a holiday weekend driving down the highway when the cruise kicks off and all the lights on the dash starting lighting up one by one or groups of two or more and my power steering goes away. I pull off at the next exit, thinking I had throw a belt and stop the car. I will not re-start and doesn't even have enough power to role down the windows. An emergency tow later to a really nice family garage and we discover it is the alternator.

After reading the post below (granted, it is 13 years old, but still...) might this AC issue been a precursor or warning sign to impending death of my alternator?

From: https://www.subaruforester.org/threads/alternator-light-brake-light-came-on.100126/#post-1087383
Alternators were introduced in the late 50's, early 60's for a number of reasons. Lighter, smaller, much longer life since automobile's used a DC generator with Permanent Magnets which were heavy and had a lifespan of 5-7 years max. Their ONLY advantage was their ability to produce power from the time you turn them without ANY voltage input.


One of MANY ways an alternator goes bad is if internal diodes fail, it allows A/C into the cars electrical system.

The Alternator, by name, produces alternating current ( AC ). It needs a small amount of DC input on the rotor to produce the 'excited' field to the stator ( the stationary coils you see from the outside ).

The AC is then converted to DC via a diode trio ( usually 3 windings on the stator, therefore 3 diodes ).

Then it passes through a regulator, which keeps the output constant after the alternator reaches a minimum rotating speed.

NOW TO THE WAYS THEY CAN FAIL ......

No Output ...... as long as the exciter field had a minimum amount of power, this can be any of the internal components from the regulator, diode trio, stator, rotor, slip rings etc.

Low output ... battery needs external charging, many jump starts ...... usually the regulator fails

High or output not regulated at 14.1-14.5v, this is the regulator failing. Usually the battery shows signs of overcharging ( battery needs water regularly, lights burn out quickly, light seem brighter than normal ) Many newer ECU's will set a code for high voltage and may even shut down to protect themselves.

Now your failure, any or all the diodes in the trio fail, now AC is directly inputted to the car. Battery fails to charge, some accessories don't work, maybe radio. Dash lights, which have a check diode in their circuit to light them when you "START THE CAR" so you can see if the bulb is working, now have AC on them, so they conduct in REVERSE current flow hence you see them come on dimly when they should not be.

On Subaru's, the wiring diagrams do not show these as they are part of the dashboard printed circuit board. The only things wired to the "BRAKE" light are the fluid level switch and hand brake switch. REMEMBER SWITCHES .... ALL OR NO CURRENT FLOWS. So if these circuits are open ( handbrake off, fluid level high enough ) there is nothing to conduct power to that light ..... EXCEPT the Check Diode .... and when it has AC applied to it, it WILL conduct for each 1/2 cycle ...and the light illuminates.
 

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The AC being mentioned in the old post deals with Alternating Current(AC) and has nothing to do with the A/C in the HVAC(Heating, Vent and Air Conditioning) that you are writing about.
 

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I also had intermittent AC issues, but after examining the situation, it turned out to be related to the relay that powered the cabin fan. In my case the compressor would stay running but the cabin fan would not.
 

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2014 Forester 6-Speed Stick
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Discussion Starter #4
The AC being mentioned in the old post deals with Alternating Current(AC) and has nothing to do with the A/C in the HVAC(Heating, Vent and Air Conditioning) that you are writing about.
Yes, I do understand the difference between AC (Alternating Current) and A/C (Air Conditioning). My point was, could a weak, or fluctuating, alternating current lead to intermittent running of the Air Conditioning?

As it turns out, the Air Conditioning issue appears to have been an air gap issue and I seem to have fixed it after removing one of the spacers.A brand new alternator did not seem to effect the Air Conditioning issue I was having, so I started looking at other possible causes.
 

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Yes, I do understand the difference between AC (Alternating Current) and A/C (Air Conditioning). My point was, could a weak, or fluctuating, alternating current lead to intermittent running of the Air Conditioning?

As it turns out, the Air Conditioning issue appears to have been an air gap issue and I seem to have fixed it after removing one of the spacers.A brand new alternator did not seem to effect the Air Conditioning issue I was having, so I started looking at other possible causes.
Yah, the alternator produces AC current, but internally using diodes converts that to DC. So AC is never seen by any car/vehicle.

Glad you got the A/C fixed. That air gap thing is a nuisance.

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