You can use a single stage thermostat on a 2 stage furnace. Usually they
will run on low stage for a certain time (around 10 min. give or take)
then kick up to high stage after that. Depending on the way the furnace
is sized, and the outside temperature, they will usually cycle off
before that time though. Most furnaces have either a set of dip switches
or pins/jumpers for sigle/two stage thermostats. On some you have to
hook up W1 and W2 on the board, others just W!, and I confess I do not
remember on a Carrier. Do you have the instruction manual for your
furnace? If so it should tell you . Good luck Larry