I have a new rheem single stage 50btu gas furnace. When the blower kicks on the air is cool and when it kicks off its cool. The installer said there is no adjustment for this it is pre set at the factory. I have some friends that are telling me this is adjustible the blower kick on air temp. and kick off temp. who is correct?

Not if it is a high efficiency furnace. It is all programed by the circuit board.

Not if it is a high efficiency furnace. It is all programed by the circuit board. its only a 80 percent unit. I'm understanding that there is supposed to be a jumper on the board for different temp. when the blower comes on and off but cannot find one. You are probably right then.