Are you measuring this the 24 volt supply side? If it is then you may have a bad transformer, or some type of short which is pulling the voltage down to 2.2 volts.

Thank you for your reply. I'm measuring on the primary side. I've disconnected the transformer and measured it directly from the electrical line.

Are you saying the 120v supply is measuring 2.2 volts? If that is true then you either have a bad circuit breaker or an open/poor connection somewhere back to the circuit breaker panel.

Yeah, the 120v supply line is measuring 2.2 volts. Circuit breakers are fine I even replaced the one for the furnace yesterday. I noticed that the supply line doesn't run directly from the circuit breaker to the furnace, any idea on what else it could connect to (maybe the outside unit)?

If the AC is part of a spilt system with an outside condenser, then the supply to the outside should be 240V. It sounds like there is an electrical problem somewhere in the house.

Have you done any recent work in the house where an electrical line may have been cut or altered?

Fuses on the outside disconnect?