I have a 2001 discovery2 and I am having some weird issues with my ac and radio.

to start the radio is not stock but used the pre wired harness from crutchfield and eliminated the interference this winter when I changed it. I have also recently replaced the alternator with a factory Bosch remanufactured one, new optima red top battery, new positive battery cable connections, new belt, water pump, idler pulley, and other non electrical related items (thermostat, hoses etc)

now that it is summer in Texas and been near 100f+ for a bit the ac is getting run full blast whenever the wife is riding with me. When it is on with the radio I am getting a high pitch whining noise, turn it off and it goes away. I only have a continuous voltage reading on my radio head unit (I know I need an ultra gauge) I get a reading of 13.3-13.9 with no ac and 100 degree temps. When I turn the ac on it drops to 12.7-13.2. It hasn’t thrown a low voltage code or gone into limp home mode but the whine is annoying and I assume might be causing other issues.

any ideas what could be causing this? I have thought bad ground possibly and checked the interior connections behind the panel near the passengers feet. It looks clean but I am unsure if the single wire connected directly to the bolt is stock or if the previous owner added/re-routed something. (His work was not great to say the least)

the only other issue I have had with the electrical is the small signal wire on the back of the alternator was broken at one point so I repaired that but maybe I need to pull the wire further back and replace.

im hoping this is not the ac compressor going out and the pulley/clutch is causing charging issues but I will say it takes a while to cool the car down and if you ask my wife it never cools down!

the picture is the ground connections I am referring to.

 

With the voltage dropping to 12.7 my first suspect would be that your new alternator is bad. I’m assuming it didn’t do this before replacing it?

 

The old alternator was having issues so I tested it and it was bad so had it rebuilt and still had issues so bought a new one and have had it tested since and it is good. What else could cause this? Any ideas?

I can always take it out and test it again but wanted to see what else I could check first

 

When you say you are getting a "high pitched interference".... do you mean from the radio? I am wondering if changing to new alternaor might have caused electro magnetic interference with the stereo system? Or are you referring to a mechanical whine?

 

My next step would be to check (clean) all the main power wire connections both positive and negative. Battery, starter, main power grounds etc. If your alternator is good, you’re losing power somewhere. To confirm that your alternator is good, put your voltmeter probes, red on the main power terminal on the alternator itself, and black on the alternator case itself. If it reads close to 14v but you’re only reading 12.7 at the battery, your cables or connections are bad. If it’s 12.7 at the alternator, I think you still have a bad alternator.

 

it sounds like the alternator whine I had with the bad alternator but it only exists with radio and ac on where as the bad alternator it was anytime the radio is on. If I turn the ac off it immediately goes away but it is in sync with the gas pedal so hit the throttle the high pitch noise starts.

 

I will check all of those and see if one of them stands out as loose or corroded tonight and check the voltages. Should the alternator voltage be the same regardless of ac compressor being engaged?

 

It shouldn’t be down to 12.7