have an old system. in the summer, the ac was turning on and off when it should be running consistantly. i noticed the little motor/switch or whatever mounted on the inside left wall of my ac/furnace (natural gas) unit would make a noticable 'winding' sound which would escalate right before turning off the blower. if i tapped it with a hammer when it started to make the sound, it would stop making the winding sound and the unit would remain on.
now that the colder weather is here, i'm experiencing a similar problem when the heat kicks on.
please advise - thanks!