Help from anyone who can. Yesterday my Central Air stop working. I have a Lennox HS series dated 1988.

I went outside & checked all of the breakers, they were working correctly. I pulled the panel off of the unit & checked out the wires inside. The looked old but all in well repair. As I has checking the conections I accidently pushed in a black plastic part that made contact when pressed in & the unit fired up. When I let it go the unit shut off. Is this a switch that is causing my problems? Please advise. Thanks

 

Sounds like the contactor is bad is this on the compresser.

 

you were pushing in the contactor, the problem most likely is the controls that send the current to the contactor electromagnet to make it pull in, you see the contactor is pulled in by magnetic force from a electromagnet when 24 volts is sent to the base of the contactor, if you look closely you will see some small wires connected at the base. With a volt meter you can check the base wires for 24 volts be sure your thermostat is set to cool and the temp is set so the unit should be running if you have 24 volts there and the contactor is not pulling in simply replace the contactor as the coil is burned out. Now if you do not have 24 volts there we will have to determine the next step so post back your results ASAP .