Re: [A/S] Digest Number 1368

["Dash7 (Michigan)" <dash7_@xxxxxxxxxxx>]

Conrad and Trisha,

I had a similar problem with my home furnace a while back and I dug out the 
manual on the 1125TG from our 68 Overlander to see if the furnace functions 
were similar and the are.  The problem is probably the air circulating fan 
is coming on too soon.  My 1125 manual shows the following sequences.

When lighting the furnace, holding down the thermocouple override switch 
will also starts the fan to clear the firebox of propane vapor prior to 
lighting the pilot.  Once the pilot is lit and the thermocouple come up to 
temperature, and the override is released, the fan stops and the pilot 
continues to burn.  The exhaust gases are expelled via the convection 
process.

When the thermostat calls for heat, it opens the main gas valve and the main 
burner lights.  When the heat exchanger reaches a predetermined temperature, 
a sensor turns on the fan to circulates the hot air through the coach.  When 
the thermostat is satisfied, it shuts the main burner off.  The fan will 
continue to run until the heat exchanger cools to about 100 degrees and then 
it will shut off .

If the fan comes on too soon, before the heat exchanger comes up to 
temperature, it will blow cool air.  Because the fan removes heat from the 
exchanger almost as fast as the burner can supply it, the output air will 
feel only slightly warmer than the ambient air and it will take a long time 
for the coach to warm up.

If the furnace in you AS has a similar sequence, I suspect the sensor in 
your furnace that controls the fan is turning on too soon.  You might try 
running this little check.  Start when the furnace main burner has been off 
for a while (cool heat exchanger).  Adjust the thermostat to call for heat 
and note the time between the main burner lighting and the circulating fan 
coming on.  I would expect a delay of at least a minute or two.  If the fan 
comes on sooner, that’s the reason for the cool air.  Perhaps someone with a 
similar furnace could run this check and give you an idea of the typical 
delay time.

Don (MI)