Re: [A/S] Furnace

["Mr. Joy H. Hansen" <joytbrew@xxxxxxxxxxx>]

Hi Steve,

You seem insistent on doing your own work without the benefit of a service
manual or experience.  I obtained the service manual for a '72 Safari and
it's supposedly the first year that such a manual was available.  Since you
said that your unit was a 1972, I thought I'd take the time to quote from
the manual.  I've added notes in double parens ((*)) and then followed the
manual quotes with notes of my own opinion.

2. Heater Removal and Replacement NT-22, 23 and 25 foot - L.Y.

1.  Shut off gas supply.

2.  Unsnap heater face latch.  (To gain access to latch it is necessary to
cut approximately a 3" square hole in galley shelf directly over the latch
area to allow latch to swing up.)  (A 3" hole saw could be  used if you are
careful to   damage the heater.)

3. Remove heater cover face.

4. Remove (4) screws from the exterior vent.  ((I found 2 additional screws
in a stamping on the exhaust port that were covered with caulking in my '69
Safari 23'))

5.  Disconnect gas line.  ((I also shut off the valve at the furnace and
with two wrenches - one on the valve and one on the flare nut closest to the
furnace disconnected the line.))

6.  Disconnect wiring.  (( Be sure battery is disconnected and 110 volt
shore line is disconnected.  Mark the wires with colored tape so that cuts
or removal of wire nuts will allow wires to be reconnected exactly.  I use a
colored marking pencil for this purpose.  If wires are identical in color as
with the thermostat, use two colors on the same wire.  I wrap the wires with
clear packaging tape as a more or less permanent marking.  I also installed
a Radio Shack 4 pin connector on the bitter ends of the wires so I would
have an easy time with reinstalling or future maintenance.  If you do this,
be sure the connector is rated for the line current.))

7.  Remove (2) Screws in lower face of heater unit.  One is located above
fan switch, one located on opposite side, same location.

8.  Heater unit can now be removed from heater cabinet for servicing.  ((My
note again,  DO NOT ATTEMPT TO REMOVE THE FURNACE CABINET.  The furnace will
slide out of the CABINET on rails.  Watch the case as some projections on
the furnace may prevent the furnace from sliding completely out.  Use a pry
to lift the locking projection.  Be careful with the asbestos seals on the
intake and exhaust tubes.  Look at the rubber boot and see if it is heat
damaged.  It is glued to the outer skin.))

9.  Replace by reversing above procedure.

10.  When reinstalling, heater unit fits into a track of the heater cabinet.
Make sure these engage properly.

11.  Hole in galley shelf can be covered with a piece of shelf material
secured in place with a 1/2" by NO. 8 sm-screw in each corner.

CAUTION: Check for gas leaks.  Make sure exterior vent is sealed.

My notes again:

I read in the service manual where the motor/blower assembly provides for
circulation of air through the ducting AND circulates air through the
combustion chamber.  Both squirrel cages are operated from the same motor,
yet separated by sealed compartments.  If the motor isn't running, the
furnace wouldn't be betting proper combustion air.  Seems like one of the
first checks would be to check the 12 volt fuse to see if it's blown.

When the furnace cabinet face cover is removed, you can see
a small screw cap with a chain retainer.  It's my opinion that this port
allows a service person to look at the flame.  If you look at the flame
before you start the vent, etc. disassembly, you can record the appearance.
It should be a blue flame with possibly a tinge of orange at the tips.  Your
owner's manual tells how to adjust the flame as this is a normal routine
maintenance chore for an owner.  If you choose to do this first, there is an
inspection port in the lower left that exposes the pilot.  This port would
be  used to ignite the pilot if the manual striker didn't work.  The owner's
manual says that there is a knurled rod that is turned to adjust the shutter
for the flame.

With restricted furnace air intake, raw fuel could be burning out into the
exhaust port (giving you lots of black stuff).  The burning fuel at the
exhaust port can produce abnormal high heat in the exhaust (having oxygen
from outside as the fuel exits and ignites.)  Remember that the plenum
should remove much of the high temperature heat with forced air from the
fan.  The excess heat in the exhaust port could burn the rubber boot around
the air intake tube.   Be sure to check this boot if you remove the furnace
and replace it if necessary.

It's also true that spiders could enter the burner shutter and block air to
the burner.  This could only happen if the screen over the intake/exhaust on
the outside is damaged.  If you painted the screen, it could reduce air
intake and exhaust enough to interfere with proper operation of the furnace.

About this time you might be crying in your beer, or relaxing and having a
beer?  After you sober up, do first things first - work smart!

                                             Regards,  Joy