Dash/Heater/Air
Conditioning Project Version
1976 GMC ex
Bob Gummersall
Summer 2004
A Little Background –
We have completed
the restoration, updating, and refurbishing of our 76 GMC Living area in the
fall of 2003. The project involved
removal of all the old
The chassis
components were also restored (rebuilt engine, transmission and 3.42 final
drive, re-cored radiator, rebuilt front end, new transmission cooler, disk
brakes on the front rear tandems, tires, shocks, etc) to allow us to enjoy some
great camping. We installed a 4KW Honda
Generator, 1.5 KW Heart Inverter/Converter/Charger, two 4D AGM Batteries,
digital tank monitor and a new master switch panel completed that phase of the
project. Our objective is to
restore/rebuild/redesign to make the GMC provide 10 years of motor coaching.
NOW THE NEXT
PROBLEM –
We knew from
having traveled about 7,000 that the stock dash air conditioning system left a
lot to be desired. I had charged it with
DuraCool, but there still was just not enough cold
air for comfort. Traveling in August to
one rally, we ran the generator and the roof air conditioner, just to get
by. I looked at all the dash
modifications that I could find including the add-on evaporator/blower systems
used my many GMCers, but all seemed inadequate to really fix the problem. These add-on evaporator/blower units provide
more cool air, but that seems like it would be an appendage and not
attractive. Having driven a couple of
hundreds of thousands of miles in other motor coaches, I also felt the GMC
driver’s cockpit left lots to be desired from an ergonometric point of
view. I want to be able to adjust the
airbag pressure without having to look and bend down to find the control. I want to adjust the heater/air conditioner
or radio without have to bend forward and tanking my eyes off the road for more
than a second. I want to be able to flash
my clearance lights communicating with an 18-wheeler without have to reach down
and find a knob and pull and push it. I
want to be able to switch to the auxiliary fuel tank without taking my eyes off
the road. My years driving other motor
coach and passenger buses gave me the background to design a new instrument
display and controls to be safer and easier to use.
SOOOOO- I decided
to go for it and install a whole new dash, driver’s cockpit and heater/ac
system. It was not without lots of study
and pondering. I measured and studied
the existing heat/ac flow and decided that the best thing for me to do was to
buy the components that would have been installed, if my GMC were being
manufactured today. That is the same
decision process that led to installing a water-cooled Honda Generator. I found that Acme Radiator and Air
Conditioning has complete high capacity systems that they were providing to
Class A motor home manufacturers. A
study of the current components told me that the stock compressor and condenser
have plenty of capacity to handle this new larger Acme Evaporator and blower
system, so I ordered the pieces for the project. The technical people at Acme were very
helpful with all my questions.
The new Acme unit
and the original control head in the background.
So the first step
was to remove the old dash and heater/air conditioning system. This took a couple of hours, since I was not
trying to save anything to be reinstalled.
Like most of the 25 year old machines, the screws under the windshield
were totally rusted, so I just carefully cut the plastic and removed it piece
by piece. I saved the gauge/control pod
which has already been recycled to another GMCer. A GMCer even want
the old control head to use as a training aid.
To remove the old
heater/ac system, I first started by bypassing the heater core, connecting the
two heater hoses to each other temporarily using the temperature control
valve. I used a catch pan so as to
collect the coolant that was in the heater core. Next all the old wires and vacuum lines were
then removed. The dash control unit was
removed and old wires labeled for the installation of the new unit. The only wires needed were 12vdc, ignition,
instrument lights and the wire that goes to the compressor clutch. The new Acme unit does not need the stock
high speed fan circuit that feeds the higher voltage directly from the
alternator to the fan through a relay.
So I removed that relay and its associated wiring. The old red wire that goes directly to the
alternator was properly disconnected, labeled and protected because it is butt
joined in the wire loom to the main wire that comes to the isolator from the
alternator. The plenum that holds the
heater core and the evaporator is held in place with 5 bolts through the
aluminum firewall. Once they were
removed, the unit could be pulled out through the opening where the grill was
removed. I had to temporally move the
auxiliary transmission cooler to the side to allow space. It weighs about 40 lbs so care has to
exercised, so as to not do damage to the radiator, condenser or anything else
that might be in front of the firewall.
This old unit came out with less than 1/16th of an inch
clearance between it and the top of the radiator framing. It took a little tug to get it out. Once past that frame, it was easy to let it
down and out of the grill area. With
all the old stuff removed, you can now start positioning the new Acme components.
I did not like
having to go inside the glove box, and remove a cover to gain access to the
fuses, so I separated the fuses from the connector that goes through the
firewall. This required removing the
black tape covering of the wire loom. It
separated nicely, so that I could leave the connector in place and have the fuse
panel on a long cord for placement in the new dash so that the access will be
easier.
All the new Acme
pieces fit into the space available in the GMC with a little shoe horning. I had to add a short length of 6” pipe and
2”x14” return air pipe to adapt the Acme unit to the GMC firewall shape. The rest of the pieces fit. The Acme defrost registers are shaped to fit
through a ¾ inch panel, like in new motor coaches. This required me to make a template, and cut
the flat aluminum right below the windshield in such a way as to have the
defrost registers at the right height for the new Dash Top. I used a high quality jig saw with a metal
blade to cut the unusual shape for the new defrost registers. A little sealant made them air tight. The defrost hoses have to come from the new
Acme Plenum back through the firewall and then up to connect with the
registers. There is room for all this to
happen, even above the brake and steering wheel assemblies in the GMC. The connection between the evaporator/heater
chamber and the inside plenum/fan module required that a 6” hole be cut through
the firewall.
Plenum/blower
mounted inside.
Because the Acme
is designed for a new motorhome that uses a metal lined 1” plywood firewall, I
had to install two ‘stand-off’ elements out of wood, to provide more space
between these two units. I simply glued
two wood pieces onto the GMC aluminum firewall spaced to allow the attachment
of the plenum/fan module with some wood screws.
This made it necessary to extend the fan inlet to the heat/evaporator
module and I used a neopreme sewer coupling from the
local hardware store with a clamp to hold it in place.
Like always it
takes lots of words to describe what is required, but it is easy to see how this
all comes together once you start the process.
All the Acme plastic parts fit fine and were easy to work with.
I now installed
the new temperature control valve that is provided by Acme and routed the
heater hoses properly. Again I used a catch
pan for the coolant that got away. The
Acme valve is electrically controlled, so the new wiring was routed through the
firewall. Acme provided a cabling loom
that would normally have been used in a New Damon Motorhome and I found that it
was generous in length and ok to work with.
Besides the wire to the water control valve, a wire needs to go trough
the firewall that connects to the evaporator thermostat. One vacuum line has to be routed to the front
of the firewall that controls the outside/inside air valve. All the vacuum lines are color coded so they
were easy to route and install. I spent
some time dressing the vacuum lines and the wiring loom with plastic conduit to
make it look nice and protect it from all the vibration of driving this wonderful
old machine.
I positioned the
hot air and cold air registers in the new dash board along with a 2” by 14”
hole for the return air register. This
required the fabrication of a rectangular duct about 20” long, that I trimmed
as I fitted it into the hole cut in the firewall and
butted it to the new Acme Control Head.
I used some adhesive backed door seal material to line this joint so as
to provide a mostly sealed joint.
Now I started the
testing process. The heater core was
properly connected and I did a cold weather test. None of the air conditioning elements were
connected during this testing. I started
the engine and got some hot coolant circulating through the heater core. Shut down the engine and refilled the coolant
reservoir. Started the engine again, and
tested all the heat and ambient air flow conditions. Immediately, I was happy with the amount of
air flow from all the registers. So I
got hot air from the floor heat registers and hot air out of the defrost
registers. Now I turned the heater
demand valve off and got ambient air from all the registers. I was impressed with the air flow and
hopeful for lots of cold air, when the ac functions were checked out.
A good friend who
is a certified refrigerator technician and I started to test the AC
function. While testing for leaks, we
found that the connection at the compressor and the OEM hoses leaked, so we
decided to replace the compressor and have new hose assembled. I decided to stick with R134A refrigerant for
lots of reasons that I may enumerate later.
I know that many of you are using the new blends like DuraCool, but I decided to stick with stock stuff. My buddy recommended adding an accumulator to
the system to protect the compressor from damage. So now with a new compressor, new hoses, new
evaporator and expansion valve, new dryer, and a new collector (recommended by
my buddy) we are ready to test. He
started by using nitrogen to pressurize the new system. After hours, it held the 100 psi test and he then used a vacuum pump to pull the system
down to -40 psi.
He then added the proper lubricant to the system and charged it with
R134a.
The initial
testing of the new system showed that the capacity can reduce the ambient
temperature about 35 degrees. This test
was done by bypassing the thermostat in the evaporator and the pressure switch
so as to test the maximum cooling capability.
In most roof air systems, if you get a reduction of 24 degrees from
ambient, the system is working great.
Needless to say, I am extremely happy with this temperature drop. The real test of this design will be driving
this summer in high ambient temperatures and see if we can duplicate the 35
degree drop. I am satisfied that I now
have a modern dash air condition system that has lots of cooling capacity. I hope that my bride of 48 years is happy on
the next trip in hot weather.
Gauges
and Controls
I am finicky about
the driver’s cockpit arrangement and where all the controls are located. I have lots of experience driving over the
road buses, truck, school buses, and motor homes, so I have developed a list of
requirements related to the ergonometrics of driving. The ideal situation is that the driver can
activate any control without looking at it, can see every important gauge with
a slight glance and can reach every function without moving in the driver’s
seat. That is what I have tried to
achieve in with this project.
The Control
Switches have been relocated to a panel on the left of the driver so that by
feel, every function can be located and activated effectively. It is important to me to be able to know
where every switch is located, without having to look down. For example, I have located separate lighted
toggle switches for the head lights and the clearance lights. These switches actually control 30 amp relays
that do the control. I can, without
looking turn off and on the clearance lights without affecting the head
lights. That allows the good neighbor
signals between me and truckers on the road.
I can flash on and off the clearance lights without affecting the head
lights. Some people call this the ICC
light function. On my side control
panel, I can feel the right and left air bag switches along with the automatic
level control switch to control ride height.
I can also feel the Fuel Tank Selector Switch without looking down. To me, this is very important for safe
driving.
Recent testing
showed air coming out of the four registers at 34 degrees with ambient
temperatures in the 80’s. This was on the
highest fan speed and Max A/C, ie all air returned
from the cab to be cooled again. We were
traveling at this time and were very comfortable with the fan on the lowest
speed with Max A/C and the outlet air was in the 50’s.
DASH AND
INSTRUMENT PANEL CONSTRUCTION
It was necessary
to construct a new dash and instrument panel to accommodate the new heat/ac
hoses and plenum. Our last coach was a
1999 Monaco Dynasty and I did modification inside that dash board to
accommodate new electronics and instrumentation. I became familiar with how that dash was
built and decided to copy it for the GMC.
The design allows all pieces to be removed after they are upholstered to
allow access for repair, service and modification. The result was six major upholstered pieces
that interlock with 8 hidden screws and four that are covered with upholstered
buttons. The two side panels are screwed
into the existing aluminum channel and held in place on the bottom with
downward pressure into the carpet. The
driver’s side panel is wider than the passenger’s to allow control
switches. Fuel tank selector, air bag
controls, head and clearance lights, wiper/washer control, control of toad
brake, emergency battery connect switch and the switch for the alarm system are
placed so that each can be reached by the driver by feel and without having to
move in the seat. I believe this
arrangement provides the maximum safety.
To hold the ac registers there is one panel in front of the driver and
another in front of the passenger. This
allows maximum cold air flow directed at the people. These two panels are fastened with blind
screws to the side panels and to the firewall.
There is one
center panel with three surfaces that contains the plenum, blower, wiring and
hoses. It is blind screwed into three
1”x1” wood battens that are glued and screwed to the firewall/floor. It has the cab air return register in the
bottom front and two registers for hot air.
This provides the base support for the dash top and instrument
panel. At the driver’s side lower area
next to the accelerator, there is a blind door that hides the fuse block. There is also the cigarette lighter located
to power 12vdc devices.
The dash top is
made of ½” plywood with the cover for the instrument pod permanently
fastened. It is held in place with 3
blind screws and 2 button covered screws that go into the aluminum channel
under the windshield glass. Slot holes
are positioned to allow for air flow from the defroster plenums. The complex shape of the instrument pod cover
provided a challenge to upholster. We
end up have to sew only one insert on the side facing the passenger. Thus the dash cover can be totally removed in
a couple of minutes exposing everything inside this area for service.
The instrument
panels are constructed from the same corian like
material that I used on the kitchen counter.
This ¼” sheet material is backed with ¼” plywood. It has two different pieces that are screwed
into the dash cover and frame. The
instruments are gauges that show air bag pressures, vacuum, fuel level, oil
pressure, coolant temperature, tachometer and speedometer/odometer. Alarm status lights for the alternator and
brakes are located center left. The
status lights for bright lights, turn signals and toad brake operation are center right. I used
miniature but very bright led lights for this purpose. Miniatures labels will be added later.
The second smaller
panel houses the radio, ac/heater control, and Digi-panel. The controls for the radio and ac/heater can
be operated without moving in the drives seat or leaning down. The radio has an infra-red remote that can be
held while my hands are on the steering wheel.
This remote control volume and station search functions.
The resulting
custom dash looks very nice and is in keeping with our restoration/remodeling
of our GMC. My bride can now recline the
Flexsteel seat and put her feet on the padded dash
like she would a foot rest. The flat
surface also accommodates photographs and flower vases when we get to our
destination.
Here is the parts list from Acme Air Conditioning
17103 SR 4 East
574-534-1516
4215043 Evaporator Kit, Class A Metal $307
4213232 Dash Set, Damon Excaper $296
4102509 5 Black Louvers $41
4100178 50' 2 1/2" Hose $27
4213202 Plenum Kit $146
4570829 Defrost Kit, Triple E $58
Freight to
Wiring Diagram
http://www.acmeair.com/wd4102804rotarywtrvlve.htm
Vacuum Diagram
http://www.acmeair.com/vd4102711rotarytauruselewtrvlv.htm
Sales Contact
Tech Contact Terry Van Warmer
Other Parts and resources:
New Compressor from
New Custom Hoses $145
6 yards of Marine grade vinyl
5 yards of ½” high density foam with a glue backing
Two sheets 4x8’ ¼” plywood
One sheet 4x8 ½” plywood
One tube industrial grade polyurethane glue
A Bride that is willing to put up with my antics and sew a section
into the dash cover
Lots of staples and some Industrial strength spray on contact
cement
Some old arthritic hands and fingers to stretch the vinyl, while
operating the staple gun