trouble with a CP9C furnace

[Larry P]

one of my contractors has 2 CP9C080B12 Coleman furnaces that will not come out of low fire in the test mode and refuse to modulate much past 40 %, the contractor hs changed the board , the motor, the transducer and the air temp disharge sensor , Any ideas ?

[Diceman]

Change contractors.:whistle:

[Larry P]

i thought about it ....lol

[Freezeking2000]

Ductwork?

[Larry P]

the ductwork is sized well seems to be more mechanical even when you put it into test mode the staging fails to take place