11 days after Sierra Shell mechanics repaired my trucks AC system, truck displays warning symbols on dash and suddenly loses all power. My neighbor looked at battery and adds water to 2 dried cells. Then I get a jump start. Engine starts and then stops a minute later. Have truck towed back to same shop. They say it's a bad alternator. Shouldn't they have checked the Volts in alternator before repairing and installing compressor, etc?

  • Welcome to Motor Vehicle Maintenance & Repair! Jul 15 '18 at 20:36
  • 2
    It was probably the 2 dried cells in the battery that worked the alternator to death.
    – Milison
    Jul 15 '18 at 20:47
  • Why did you have to repair the AC system? Did you experience a seized compressor (loud squealing noises, stalling, broken belts etc), or AC that simply ceased working suddenly and without apparent reason and when you took the truck for the "regas" they had a look and then you were told the compressor was faulty or something along these lines?
    – Al_
    Jul 15 '18 at 21:22

If you took the vehicle in to have the AC looked at, they aren't going to be checking much else. As long as the alternator was running when it left, they aren't going to check it for function. If the check engine light was on and/or the battery indicator was reading low, they'd mention it. It sounds like from what you wrote, neither was the issue. One really has nothing to do with the other (AC compressor and alternator). They do run off the same serpentine belt (in most vehicles), but really, this is not something they'd check.


As Pᴀᴜʟsᴛᴇʀ2 said, no, they should fix just what is broken unless you are going to a dealer in which case you can expect that sort of thing.

As to the new problem, if the measurable voltage from the cable when the car is on is below 13 volts, pay for a new alternator. If it is 13-15 volts, read on. Most jobs require as step 1 that you disconnect the negative battery terminal. There's a good chance that he over tightened the terminal, stripping it, when putting back OR that he didn't torque it hard enough. Sometimes corrosion is a factor as well. This would cause the problems you are attempting to describe.

(I say "attempting" because you did bad job describing things. For example, you say lights come on, but don't say which ones. You say all power is lost, but I think you meant to say that the car stalls, but you might mean all ELECTRICAL lights go off as well.)

Anyway, in this case, yes, the new AC job caused the new problem. You can further test if it is a terminal/cable issue by measuring the voltage at the cigarette lighter when the car is on and at the battery's lead terminal (not the cable). If there's a difference, you don't need a new alternator. You can also see if any part of the cable is warm with a temperature gun or hand. (It should be cold.)

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