I have A 96 plymouth neon. I am having what seems to be a power issue, usually only if I have my heat running on defrost. I feel a surge, or rather a drop in power, lights dim and the heater seems to struggle. It only happens for a second but happens every three to four seconds, like its exhaling really hard, it causes my idel to dip slightly as well. I have no clue where to start.
Hopefully someone here does.

Could be a bad heater core or bad compressor. I'm not real familiar with the HVAC system in our neons though.

When you are in Defrost mode, the A/C compressor cycles on/off to dry the air and clear the fog off of the windows. The A/C takes a lot of power from the engine and if the belt is not in top condition, it will slip some when the Compressor comes on. The alternator is on the same belt and slippage would cause an electrical sag as well as a power sag.

How could I check/repair/tighten this belt?

How could I check/repair/tighten this belt?
You should really get a manual to help you out. Here is a link that explains how to replace the alternator, but it does show where the adjusting nuts are on the alternator.

When you are in Defrost mode, the A/C compressor cycles on/off to dry the air and clear the fog off of the windows. The A/C takes a lot of power from the engine and if the belt is not in top condition, it will slip some when the Compressor comes on. The alternator is on the same belt and slippage would cause an electrical sag as well as a power sag.

The alt is not on the same belt. I just needed to correct that the alt runs off a seperate belt. the compressor shares its belt with the power steering pump.

If i replace the alt with a better one (higher) amp, will that reduce the impact the compressor has??

Sorry, don't have my Neon anymore, thought the alt and air were on the same belt.