Trane DH1B040A9241C Series, Service Facts

20 

 UH1-DH1-SF-1L

Service Facts

Cycle power to 

furnace and call 

for heat

Ignition occurs and 

FAN ON delay 

begins

Does fan come on 

after ~45 seconds?

(Downflow models 

after 10 seconds)

Does blower 

wheel turn 

freely?

Disconnect 

electrical power to 

furnace

YES

Check set screw 

position and motor 

bearings. Correct 

or replace as 

needed. 

Check operation

NO

Is 120 VAC 

measured to 

motor?

YES

Is 120 VAC 

measured at IFC 

between HEAT-H 

and CIR-N?

NO

Replace furnace control

Check operation

Repair wiring harness.

Check operation

Are filter & 

blower wheel 

clean?

YES

Replace filter and 

clean blower 

wheel. 

Check operation

NO

Is external 

static pressure 

greater than 

nameplate?

YES

Correct application 

or duct issues.

Check operation

YES

Is heat rise 

within 

specification?

See Service 

Facts

NO

Check motor and capacitor. 

Repair or replace as needed

Is return air 

temperature 

above 85 F?

NO

Return air 

temperature is 

above max limit

YES

Check for loose 

insulation or other 

objects within 

furnace air stream 

NO

Is outlet 

manifold gas 

pressure within 

specifications?

YES

Correct gas 

pressure

Check operation

NO

Is temperature at 

high limit above 

the switch setting?

YES

Replace high limit 

switch

NO

YES

Is temperature at 

auxilary limit 

switch above 

specifications?

Replace auxiliary 

limit switch

NO

Check for excessive 

reverse flow during an off 

cycle

YES

DEFINITION

Limit switches are safety 
devices that will open 
when an abnormal high 
temperature has been 
sensed.
REMOVE ALL JUMPER 
WIRING TO SWITCHES!
Under no circumstances, 
shall these switches be 
left jumpered when not 
troubleshooting.

Make sure any temperature 

measuring devices 

(thermocouples, dial 

thermometers)  used to 

estimate limit temperature 

are within ¼ inch of limit 

measurement point

See next page for 

additional 4 flash 

faults

4 Flash Fault LED

Down Flow Models Only

NO

YES

NO

Does motor 

continue to run 

during the entire 

heating cycle?

YES