The thermostat LCD went away (like no power to it)& the system is not working at all. Rheem Corsair 2001. Downstairs unit is bigger for a 1700 sq ft home. Friends have stated that it could be fuses but I can find none. Looked for fuses for indoor unit but it appears as though we only have a circuit breaker. I can push on the contact on the outside unit & it works but there is something between that & the thermostat that is not working.

Furnace/airhandler,if its gas,it might have a push-in type fuse in the circuit board(sometimes hard to find) turn off breaker to the furnace wait a minute and back on,sometimes needs reset
Also possible fried transformer (which feeds power to thermostat and controls ?

Make sure batteries ar good in thermostat

Thanks to both of you. We'll be checking these things. These are the things we've done so far...
Looked for fuses for indoor unit but it appears as though we only have a circuit breaker. I can push on the contact on the outside unit & it works but there is something between that & the thermostat that is not working.