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Weird electrical(?) issues

I recently discovered (the hard way) that my AC pulley was completely destroyed. I don’t currently have the money to fix it so I bought a smaller serpentine belt to override it for now. Every seems to be fine but…
I was driving on the freeway today and my car seemed to stop shifting. I was going 70mph and car was running at 4000rpms. It’s a mild winter here in Michigan but this happened right as I set my heater to defrost for some fog on my windshield. My car auto locks when in driving gears and it unlocks in park; this also stopped working by the time I needed to get out. I checked all of my fuses and my transmission fluid level. All seems good.
When I turned on my car again, everything seemed normal. By this point, I was back to just using my vents for heating. I drive about 30 minutes to the next town over, fog on my windshield again prompts use of the defroster, and I do so when I am close to my destination. Well, wouldn’t you know it… my engine abruptly jumps up to 4000rpms again. When I stop at my destination, the car doesn’t automatically unlock when I go into park.
What is happening?!

Edit: I can confirm that car is downshifting when I go to defrost setting and then overcompensating with the engine.

When you bypassed the a/c compressor, did you unplug the electrical connector on the compressor? If you didn’t you should have. When you switch to defrost, it’s energizing the compressor clutch. I don’t know why this messed with the auto-locks, but I always thought the Saturn Vue was a strange car. I believe if you unplug that connector, your other problems may go away.

Maybe the belt invention is causing the alternator to spin too slow somehow. Do a couple of voltage measurements. Before first start of the day the battery should measure about 12.6 volts. Immediately after starting the engine, 13.5 to 15.5 volts. what do you measure?

I suggest you have the alternator checked to see if there is excessive AC ripple voltage coming from it. Excessive AC voltage in the charging circuit can cause strange electrical things to happen.

Also check ground straps between body and engine, negative wire(s) to the battery etc.

That was my thought. My dad also advised I disconnect the compressor and then see if I still have the defrost glitch.
I’ll update you later on the results. For now, it is continuing to return to normal when I move away from the defrost setting and restart the car, but only then.

Check to see if the problems occur when you have the headlights on HIGH along with the blower on high. This will put a pretty good load on the charging system and if the problems return then the alternator should be checked out.

@George_San_Jose1 @Cougar I don’t mean to ignore you. My battery and my alternator are new.
@old_mopar_guy I just unhooked the compressor. No more problems when I go into defrost.

Fantastic. Glad to hear it.

It is good to hear that disconnecting the compressor cleared up the issues but I don’t see how a problem with that could cause things like your locks not to work correctly.

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Software glitch? The engineers at the factory probably don’t test the engine configuration where the AC compressor isn’t spinning. I expect that is confusing the car’s software somehow.

@Cougar @George_San_Jose1 That’s what my mechanic friends say. The locks themselves still work. The auto/safety locks that work with the gear shifter stop working though. It has got to be a software problem then.

Even though the alternator has been replaced it is still possible that there could be a problem with it. To see if that is the case all you need to do is disable it. Remove the connector with the small wires that connect to the alternator. Don’t mess with the main output lead which is HOT to the battery. With the connector disconnected start the engine, go for a short test drive and see if the lock system then works as it should. If it does then you need to replace the alternator again because it is generating excessive AC voltage.