I just had my furnace replaced last winter with a brand new carrier Gas Furnace/AC unit. It worked fine all last heating season, now when I turn on the heat, it won't fire. The central air unit also didn't work this cooling season. The fan won't even come on when I switch it to on at the thermostat. It clicks at the thermostat but nothing in the furnace. It is electric ignition so no pilot. Gas is on, power is on at the box and at the switch on the furnace. Batteries in thermostat are brand new. Where else should I look?

I just had my furnace replaced last winter with a brand new carrier Gas Furnace/AC unit

The unit will still be under warranty as long as it was installed by a authorized Carrier dealer. I would call them before you mess with it and VOID the warranty.

Not sure that it was. It was installed by friends of the landlord, who may or may not be authorized. I just don't know that much. Guy was supposed to show up twice to look at it and never showed.

If it is rental let the landlord do the repair. The problem you can get into is the fact that as a tenant if you mess with it the landloard can blame you for the problem. My rental and lease agreements specifically forbid the renters from messing with anything in the unit.