HVAC barely blowing air out of vents and lights dim every couple of minutes - why?

[MikeyS]

The HVAC is between 20 - 30 y/o. The unit outside (compressor?) is running. Air is coming out of the vents, but barely, so the A/C is hardly cooling the house. The lights in the house dim every couple of minutes, but nothing is coming on with the HVAC when they do so. When I turn the heat on, I have the same problem and it blows out cool air instead of warm.

When everything is working normally, the lights typically dim when the outside unit comes on.
The filters were changed after the problem started, but it didn't seem to make a difference.
I just want to make it clear that all the lights in the house dim every couple of minutes. Before this problem started, only some of the lights dimmed when the outside unit came on.

 

[webjnke1]

Get new filters

 

[JohnM]

The lights dim when the voltage drops on the circuit they are wired into. It's unusual, but not impossible for a compressor to be wired into the same circuit as the lights. This means that if the lights are dimming when the compressor kicks in, that you may be experiencing a voltage drop on the main service line to the house. That would be a serious condition and you should get it looked at by someone who can examine the conditions at your house.