1992 WB40 Air Conditioner replacement - directions & pics

[mbrund]

NOTE: I have two Dometic AC units that I am willing to part out
cheap to anyone needing parts. I probably could part out one of the
thermostats if someone needed one badly enough (need to find a way
to plug up the hole and hang something over it

I replaced both front and center Dometic units with new Carrier AirV
15Kbtu Heat Pumps. I choose these units because they have infrared
remote controls and the head unit is installed in the lower unit
cover. So you do not have to replace the original wall thermostats
as they just get disconnected and are no longer used. One thing to
note about newer units, they all appear to require 12 volts now,
whereas the older units installed in the BB only needed 120 volt AC
and the voltage for the thermostat was generated in the AC unit and
sent to the thermostat over the thermostat wiring harness. So you
will need to be prepared to run a 12 volt positive and ground to the
new AC units.

OK lets get started:

First make sure all AC power is disconnected from the unit (turn off
the forward AC control switches, turn off the thermostat controls,
turn off the circuit breaker, disconnect shore power, etc.).

Next you will need to remove the lower panel from the unit. In a
1992 WB40, this is a vinyl wrapped piece of plywood with a air
filter grate attached to it. The panel is held in place by four
plastic push in retainers (see "dometic lower cover push pin_*.jpg")
that are pushed into holes drilled into the ceiling plywood. The
retainers are located about 1" to 2" in from each front and rear
corner. You can open the filter grate and grasp the lower unit at
the front with your fingers and pull down and get the forward of the
unit to pop out of their holes, then grasp the panel along the sides
toward the back and do the same thing.

Once the lower unit cover is removed, you will need to disconnect
the power lines at the lower unit (see "dometic electrical
box_*.jpg"). Then remove the screws located inside the electrical
box as the electrical box covers one of the retainer bolts and you
can only get at it if you remove the electrical box. You can also
remove the thermostat harness at this point, one side of this
harness has a latch, you can see it in the picture "dometic
thermostat wiring latch.jpg", press on this latch and pull the two
halves apart.

Next remove the lower duct diverter cover (see "dometic lower w_o
cover.jpg"), believe there are about 18 phillips screws here. Once
you remove these screws, if the lower unit has silicon sealer around
the edges sealing it to the upper unit (see "dometic ducted
assy_*.jpg") you need to score the sealer with a razor to ease the
removal of the ducted assy. Once the screws are removed and the
silicon scored, take a standard flat bladed screw driver and insert
it between the cover and the AC unit and pry the diverter cover from
the upper unit.

Next you will need to remove the four retainer bolts (see "dometic
ac retainer bracket and bolt_*.jpg). If you are replacing the
unit with a new unit that will use a new lower unit, you will need
to also remove the brackets as they are not needed with a new lower
unit normally.

The upper unit can now be removed. My upper unit seals where
siliconed to the coach roof, so it took a bit of force to break this
seal. I just grasped the rear of the AC unit as it gives you more
leverage and pulled up with consistent force until the unit broke
the seal. Then load the unit on a lift (I used a Genie Superlift,
see "Carrier ac on genie lift_*.jpg") and lower from the coach. Or
use whatever method you have to get the unit off the roof.

Now is a good time to run the new 12 volt wiring harness if your
unit needs one. This could be done in one of several ways. If you
are not using the harness for the thermostat, you could cut off the
end and twist half the wires together for the positive side and half
for the ground at the AC end, and then do the same at the thermostat
near the drivers seat. Then snake a new wire from the thermostat to
the upper forward fuse panel and install a new fuse and the
wiring. I choose to run a new wire. I did this at the center AC
unit. I drilled a hole (first one was too high and ended in the
foam insulation) low enough to miss the foam insulation
(see "Carrier 12v wiring hole.jpg"). In my coach, the kitchen is on
the street side at mid-cabin. So I removed the wiring chase in the
upper kitchen cabinets and then used a fish tape to go from the hole
to street side wiring chase. I found an unused circuit here which
was capped. It was labeled #9, and it was also not attached at the
upper front fuse panel and was capped as well. I used this wire to
run my 12V positive. Next I located a wire in the chase that was
grounded to the chassis in the wiring chase (you will have to ohm to
find this ground (mine was white in color), or just find a chassis
tubing and tap a new wire into it for the ground). I attached the
wire labled #9 at both ends and added a fuse in the upper fuse panel
for this circuit. Because I was also installing a new forward
unit, I used the fish tape to go between the vinyl ceiling panels
and the roof plywood from the center unit to the forward unit and
joined these two circuits together at the new center AC unit. So
the circuit goes from the upper forward fuse panel down the street
side upper wiring chase, then goes at mid-coach to the center AC
unit via a new hole in the center AC support bracing, it is then
connected to the AC 12 volt wiring and also jumpered to the forward
AC unit (goes between the ceiling panels and the plywood sheeting)
and connected to the 12 volt circuit there.

Next clean the opening on the coach in prep for the new unit. Get
the new unit up on top of the coach (I used the Genie lift here as
well, also used it to remove an old spare tire that was on my roof
that was the wrong size). Lift the AC unit and place it over the
opening in the roof (DO NOT SLIDE THE UNIT AS IT WILL DAMAGE THE
SEAL). If you so desire, run a bead of silicon around the opening
before you place the unit over the hole. Make sure the unit is
centered over the hole and square on the roof and then return to the
inside of the coach to finish the install.

Next, if you are using the original BB brackets and lower unit run
the four AC retaining bolts through the brackets (this may require
that you re-position the BB brackets by removing the two wood screws
from each bracket and re-attaching in the proper place). Torque
these bolts to the manufacture spec. If you are using a new lower
unit, follow the instructions to attach any wires or other items
before the bolts are secure and then secure the bolts and torque
them to specs. For the Carrier AirV, locate the new lower unit
assy, before installing the assy, attach the foam block to the upper
unit per the instruction (lining the one edge up with the edge of
the AC air outlet) by removing the paper backing to expose the
adhesive. Now attach the ducted divider to the lower unit at the
correct height for you unit (mine was the very first hole for
3.25"). Now run the four long retaining bolts (see "Carrier lower
unit mounting bolts.jpg") through the lower unit to the upper unit.
Place the three wiring harnesses (see "Carrier lower unit wiring
harness-1.jpg") that attach to the curb side of the AC unit on that
side of the electrical box, and the one wiring harness (sorry no
individual pic of this harness, you can see it on the right side of
the electrical box in pic "Carrier test unit before final
mounting.jpg") that attaches on the street side of the electrical
box. Attach these harnesses to their proper connectors on the lower
electrical box.

Next attach the new 12 volt harnesss to the red and black wires that
are located on the street side of the electircal box. There will be
two blue wires with the harness that will not be used (they are used
for AUX FURNANCE, which does not exists in the WB40).

Next insert the freeze protect thermal sensor in the condenser at
the center of the condenser. Push it all the way in at a 45 degree
angle to the condenser per the instructions.

Remove the two screws (one on each end) from the lower unit
electrical panel (see "Carrier lower cover ac wiring cover_*.jpg")
to gain access to the area where the AC wiring will be connected
Insert the plastic grommet in the hole in the side of the
electrical box, insert the AC wiring and then attach the romex wire
to the AC Unit wiring (see "Carrier lower cover ac wiring.jpg").

The unit should be ready to run at this point, so before putting the
electrical box cover back on, plug the coach shore power in, turn on
the AC breaker and test the unit. If everything is OK, turn off
the breaker,disconnect power, etc. and re-install the lower
electrical box cover. Then install the lower unit cover
(see "Carrier lower unit in operation.jpg"), turn on the power and
breakers and enjoy your new AC unit.

Note: If you need to remove any of your ceiling vinyl panels, they
use plastic retainers similar to the AC lower cover (see "Ceiling
panel push pins_*.jpg"). They are located at various places along
the panel. They are a little bit of a pain to find and then get
them to release, just be patient in locating and getting the to
release.

Michael Brundridge
1992 WB40
Georgetown, TX