Serpentine belt fell off randomly. I also found a huge dead rat when I inspected the belts. Could that have caused it? There was fur and I think guts all over the place. I towed it to the only place open Pep Boys and they put the belt (no damage) back on and I drove it home. However , he said the AC compressor was the cause and it would cost 1000 bucks to fix it. Should I get a 2nd opinion and is it safe to drive now?
The only way the compressor could cause the belt to come off is if the clutch bearing were bad.
And if that’s the case, the belt is going to going to come off again.
Tester
As to second opinion—Yes.
Find a good independent mechanic or AC specialist for a second opinion, do not use a chain like PepBoys, Firestone, etc.
As to the rat, your vehicle may have soy-based wiring that attracted the rat, but he/she did not chew on the serpentine belt.
Try turning the AC compressor by hand with the best off to see if it is smooth. I suppose excess tension could bend something.
Just leave them, the site moderator will combine them, might be several days.
There is a bit of a learning cure dealing with this (as with many) web site.
Don’t worry about it.
As to your car, rat was likely in the wrong place at the wrong time.
Likely (I do not know for sure) your car has soy-based wire insulation, unfortunately this attracts rodents. After you get your car diagnosed and necessary, if any, repairs are done, obtain a rodent repellent spray for your engine.
As noted by another responder, if the AC compressor is bad, it may cause the new serpentine belt to shred. Please get a diagnosis from an independent, non-chain mechanic.
If the AC compressor is faulty the AC system may require other repairs. A legitimate mechanic/shop will likely charge a diagnostic fee, usually $100-150, may be higher in some areas. Some shops will then waive the fee if they do the repair.
Good luck with your car.
Since the old belt was reinstalled, there is no chance of a new belt failing.
I interpreted the OP as a new belt installed by PepBoys. I may have misinterpreted the post.
Yeah just keep your handle and post under maintenance and repairs usually. I pay no attention anymore to the categories. Too many with too little activity.
I can’t see how this would cause a compressor problem unless the little critter was chewing the wires when you started the car. Just clean the guts up and if rhe compressor doesn’t work, look at the wires and have a competent shop repair them. Used to have the problem with cats sleeping on top of the car tires. Then bump, another one gone.
thx. The wires look ok. The compressor works. It turns on fine. The AC blows cold and strong, no burning smell or noises at all.The only thing I noticed is the AC clutch starts and stops after a few minutes, then rolls backward a few millimeters and then starts turning again normally. Not sure if that is normal or considered a short cycling issue.The guy said that is the sign of a faulty compressor , that it is “seizing” and will cause the belt to pop off again. Making me paranoid to drive it. As it was kind of scary when the power steering got cut off. Thus, I need a new compressor. Although I blame the rat for the belt falling off. The AC has never shown any symptoms or issues before that.
I moved out of state, left my trusted mechanic and now have to find a new one. So, I’m trying to do my homework before hitting up a repair shop.
By doing homework I hope that does not mean you plan on telling the shop what to do or replace. Just tell them what happened and let them do their job. There will be a diagnostic fee and just say you want to approve the repairs before they do anything.
Ok, but nah, just when they start explaining stuff…I want to have some background knowledge to see if what they are saying makes sense.
That is normal. The compressor clutch must cycle to prevent the evaporator core from going below 33 degrees and icing (ice build-up will block air flow to the vents).
If the compressor seizes, the belt will break or slip and make a loud squealing noise. Since this has never occurred, the compressor is fine.
If the compressor is to blame for the belt coming off, what killed the rodent? Animals sleep or nest in engine compartments, when the engine is started, they sometimes get caught in the belt while trying to escape.
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Well you a/c works so your compressor5 has not frozen.
You have already learned the diagnostic skills of your Pep boys 
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Get a second opinion. My boat guy charges $100 extra if there are mice in the boat! Can’t imagine what he would charge for a rat!
The rodent is the likely cause for the belt to jump off. A seized compressor will damage the belt, it will not be reusable.
If you make it home from the repair shop and the air conditioning is cold, it would seem that the compressor is operating as it should.
Tomorrow you will be in hot water for creating more than one thread. There are people here who keep tabs on all this.
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I would not trust Pep boys to diagnose this. And don’t take it to an oil change shop or tire place either. If you A/C puts out cold air, you are OK. If you can’t tell because it is too cold out, go to a real mechanic.
How long was the light lit-up before it went off?
The light when on when I first started the car. I got the battery checked and they said it was because it was on low charge (due to the serpentine belt slipping off).It went off when I got them to put the belt back on and I started the car.
Poor rat. he was trying to put the belt back on for you, but his tiny hands just could not do it. 
I would have the belt, tensioner and idler pulley replaced.
does the A/C work? if not it could have locked up and threw the belt.
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The big question is where the rat came from and are there more in the family.
I can say it now since everyone is dead but my folks built a new house in 1965. Sealed tight but there was a corn field in back. One morning there was a large dead rat laying on the basement floor. The door to the shelter had gnaw marks on it. Mom went nuts. I still have no idea how it got in. There was an opening to the attic though from the garage was all I could think of and made mom feel better when I screened it off. Never had any more but shot guns will make a mess of them.