A/C Trouble in Toyota Tercel

Hi,

I have a '95 Tercel with a retrofit AC. This summer the A/C simply
stopped working. Taking it to the Toyota dealer, I was told that the A/C
needs to be evacuated and recharged and that it would work out to around
$170. Now, after this was done, I was told that the A/C was atill not
working as it needed the amplifier to be replaced and that they could
not give me a qoute on it as their parts shop had no power. We had a
thunderstorm at that time and they had a pwoer failure. At that point I
thought the amplifier was a small part so I didn't create any fuss.
Later, calling them I found out that the amplifier is another $300 or
so. Now, my question is, should they have been able to figure out during
the problem diagnostic itself that the amplifier needed to be replaced
or is it something that they could not tell without evacuating and
recharging the A/C?

Thanks,

-M