First things first, you need to see why the check engine light is back on.
Just because you replaced 2 sensors a while ago doesn't mean one of the 40
others isn't going out of spec either.

As for the transmission, check the fluid level and make sure it's up to par
and sniff it, if it smells burnt then have it serviced, otherwise, it could
just be a lot of miles on it.
the a/c sounds like the switch could be bad or the connector to it is loose.

for the jump starting, I'd have the battery charged and tested as well as
the alternator.

Here's what I'd do.. Find an Autozone and bring the car to them and have
them check the battery and alternator, they can do this on the car.
IF the car wont' start do this.  If the car turns over, but doesn't fire up,
it could be a lot of things, but have the timing belt checked out.
If it does start, head to Autozone.  Also see if they have the means for the
check engine light.  Usually they just do the cars from 1996 on up, but they
might do a car that's older.

Sounds like you don't take care of it...and don't care to.

Get rid of it.  Then buy some cheap car because it sounds like you beat
the s--- out of cars and the new one will no doubt be "falling apart" in
a few years.

Altimas are well-made.  I had a 94 until last fall and hardly ever had a
thing go wrong with it.  Same is true for many other Altima owners I know.

John

Actually I have taken good care of this car. I do not do any of the repairs
but in the past 4 years that I have owned it I have replaced the entire
exhaust system 2 times, oil change every 3000 miles, new battery and
alternator, sun visor repaired, air conditioning repaired, driver side
entry key lock replaced, oxygen sensor replaced 2 times, tires, have had 3
complete tune-ups one in which the dealer put in the wrong plugs which by
the time this did its damage the dealership had gone under. I feel maybe
the only thing I did wrong was to only have Nissan dealers work on the
car. By the way, in the past 4 years I have owned the car we have put
12,000 miles on it. It is in the shop too much to drive it much. Our other
car is a Toyota, which other than regular maintainance, I have not put a
cent into for the past 3 years. So dont make assumptions about people.

Sorry to hear about you luck with the car. Some cars get built better than
others, it's sort of a numbers game.

The air conditioner not working in any mode but full is a problem with the
A/C Resistor pack, when the fan is in FULL mode, it by-passes this device
to allow the full twelve volts to make it to the blower motor (which
generates that wonderful gust of air). This part is also called the Blower
Motor Resistor. The part shouldn't be too expensive, and replacing it
should take 1-2 hours. I can't say for sure where it is on your year
specifically, but it is generally placed by the blower motor, under the
glove box. It will have about 5 or 6 wires going to it.

Nissans are somewhat notorious for less than great electrical systems,
especially for wiring, and I've had my share of the problem. The strange
noise you might be getting from the car when you attempt to jump it may be
a very weak electric current running through the relays. In that case the
problem tends to be a dead cell in the battery. When this happens the
battery has a short in it and it absorbs all the juice from then car,
hence jumping will not work. (This has happened to me). One way to check
is to activate the Hazard Lamps (with the key off), if they dont come on,
or create an interesting buzzing noise, the battery or it's connections
are probably the problem.

I'd like to offer more help but I'd need to know what sensors are
considered the culprit for the Check Engine lights illumination. Also, if
you've replaced the same Oxygen sensor twice, there may be a fuel problem,
either with a leaking injector, or with bad gasoline. Fuel injectors are
actually pretty easy to replace on the Altima 4 cylinders. (KA24DE) The
injector could be dumping too much fuel into a cylinder, and then setting
the Oxygen sensor as failing in the Computer. This would definitely cause
the Check Engine light to come on. But this is a vague guess to their
premature failure.

Also, your car doesn't have a timing belt, it has a timing chain, which is
very long lasting, generally 300,000 miles and then some, especially when
she's getting a regular oil change.

Sorry to hear about you luck with the car. Some cars get built better than
others, it's sort of a numbers game.

The air conditioner not working in any mode but full is a problem with the
A/C Resistor pack, when the fan is in FULL mode, it by-passes this device
to allow the full twelve volts to make it to the blower motor (which
generates that wonderful gust of air). This part is also called the Blower
Motor Resistor. The part shouldn't be too expensive, and replacing it
should take 1-2 hours. I can't say for sure where it is on your year
specifically, but it is generally placed by the blower motor, under the
glove box. It will have about 5 or 6 wires going to it.

Nissans are somewhat notorious for less than great electrical systems,
especially for wiring, and I've had my share of the problem. The strange
noise you might be getting from the car when you attempt to jump it may be
a very weak electric current running through the relays. In that case the
problem tends to be a dead cell in the battery. When this happens the
battery has a short in it and it absorbs all the juice from then car,
hence jumping will not work. (This has happened to me). One way to check
is to activate the Hazard Lamps (with the key off), if they dont come on,
or create an interesting buzzing noise, the battery or it's connections
are probably the problem.

I'd like to offer more help but I'd need to know what sensors are
considered the culprit for the Check Engine lights illumination. Also, if
you've replaced the same Oxygen sensor twice, there may be a fuel problem,
either with a leaking injector, or with bad gasoline. Fuel injectors are
actually pretty easy to replace on the Altima 4 cylinders. (KA24DE) The
injector could be dumping too much fuel into a cylinder, and then setting
the Oxygen sensor as failing in the Computer. This would definitely cause
the Check Engine light to come on. But this is a vague guess to their
premature failure.

Also, your car doesn't have a timing belt, it has a timing chain, which is
very long lasting, generally 300,000 miles and then some, especially when
she's getting a regular oil change.