Need to know what it is not doing, post more info.
Heater coil
There are a couple of reasons why a 1999 Oldsmobile Alero ac heater to stop working. The heater coil may need to be replaced or the HVAC blower motor may need to be replaced.
Most likely it would be a blown fuse in the fuse block.
OK, did the blower motor actually just stop, or does it still blow but no heat?
There could be multiple reasons why a heater would stop working in a truck. There could be low coolant or a bad fuse to make a heater stop working in a truck. The best way to find out the reason is to take it to a certified auto mechanic.
Yes it could also cause the A/C to stop working.
First check the coolant level, a coolant leak would cause a heater to stop working- assuming you mean the blower is blowing but it isn't hot. A stuck thermostat will also cause you problems with your heat.
Yes it will stop heating up...........
Could be low on freon,
Crossed wires that have corroded together can cause your heater and radio to stop working, at the same time. The heater and radio are not related in any other way.
The blower motor speed switch is burned out or the fuse is blown.
Possibly a relation to the blower motor/ heater door accuators.