Another Mod Verging on an Upgrade Idea

[FrankGRUN]

As I indicated in a previous post, I have a 1982 Class C Born Free 24ft Rear Bath Coach in excellent condition with a number of functional modifications or customizations. Recently, I have become obsessed with the ivory color of the Coleman AC Ceiling Assembly. When I last took down the shroud to change the filters and repair the floppy louvers, I noticed how stiff and brittle the plastic structure had become. As an Air Conditioner and heater, the unit still functioned perfectly and surprisingly quietly. I decided to look into replacement of the shroud with a new unit. Alas, they are long gone and have been unavailable probably for several decades. The Coleman AC was a factory install in November of 1982 and carries Model Number 6246A. Searching the parts list archives, I found that my current ceiling assembly is identical in appearance to the Coleman 8330-715 (see attachment). With further study, I found that the most recent version of Coleman's non-ducted Ceiling Assembly is model number 9430D715 and is described as comparable with most Coleman Rooftop AC units. After studying the details, it is white, has a more up to date look, is thinner, has a better air volume control, larger output area and more accessible function and thermostat controls. A quick review of the YouTube video demonstrating its installation, convinced me this would be a perfect visual and functional rejuvenation of my antique unit.

Cautiously, I sent a question to a reputable Coleman vendor asking if the 9430D715 was compatible with my Model 6246A air conditioner. I was quickly told that the manufacturer said it was not compatible. I went back and studied the meager information I had in hand and concluded I had to talk to the source. I called the Coleman Tech rep, and after being warned that they really don't like to talk to idiots, I finally got through to a human! I discovered that the problem was that the mounting holes of the ceiling system mount plate would not line up (older version to newer). Now, the installation video provided by Camping World shows a view of the frame and the newer mounting holes. I immediately concluded that 1) if the holes were in the wrong place and the mount had metal in that location, my trusty drill could remedy the problem, and 2) if there is no metal in the required position, I can readily fabricate an adapter. So I have purchased the newer ceiling assembly and should have it in hand within a week. Hopefully, this project will turn out to be a happy upgrade, but I will report the progress and results should there be any interest.

Should any of you have attempted this before, please pass on comments and dire warnings!

[Matt A]

Following this as I am in the same boat.

[FrankGRUN]

Thought I would add an update on the progress of this Upgrade Approach. I now have the complete 9430D715 Ceiling Assembly in hand, along with the new heat strip assembly. In addition, I have fully disassembled the the older existing ceiling assembly and the older heat strip. After having studied both the new assembly and the underside of the older unit, there are a number of interesting observations.

To begin, I now know the Coleman Model Number of my RoofTop AC. It is 6749R707 and not 6246A as my documentation (passed on from previous owner) had indicated. Knowing the model number, I was able to go to my local dealer and get a complete printout of the parts list and component diagrams. The model number for these units is on a sticker affixed to the base of the rooftop assembly. It is accessible only after removing the ceiling assembly.

There are a number of differences from older to newer bases of the Coleman Rooftop AC units. The full assembly of the older ceiling assembly is metal (excepting the plastic shroud). The newer unit is essentially plastic except for the control box and mounting frame that goes into the 14" x 14" rooftop cutout. The older heat strip was mounted to the metal bottom of the ceiling assembly and the heating element was an open wire. The newer unit is a much higher quality construction and mounts within the return air duct. This change was necessitated by the all plastic construction of the newer unit.

The 9430D715 is affixed to the rooftop AC unit by four 1/4-20 bolts located at the corners of a plate that mounts into the 14" x 14" roof cutout. The plate and the bolts suggest that part of their function is to lock the Rooftop AC to the roof of the vehicle. The square adapter plate also anchors the rest of the 9430D715 ceiling assembly. In contrast the older unit has only three 3/8-16 bolts arranged in the rearward third of the ceiling opening. Finally, the cooled air output from the 6749R707 AC actually exits through a 4.5" x 4.75" nearly square port whereas the new ceiling assembly has a 4.5" x 8.25" opening for the cold air. I believe these port differences are inconsequential. The three 3/8-16 holding points are elongated nuts welded to the metal base of the AC unit with a length of 0.398"

As a result of these measurements I have designed a "H-pattern" bolt adapter which will provide a bolting interface for the 9430D715 and will itself be bolted in its center to the original AC base metal supports. So, just as the Coleman tech rep said, the bolting pattern is different but easily modified. The new duct interface will slip over the original square outlet with little impact on overall airflow.

There seems to be a small wiring difference between old and new, but I will address that after the bolt adapter is finished. I will be modifying the electrical wiring to add the Auto-fan Kit by AirswitchRV.com and will report the final results within the week with pictures.

Too summarize: It will work!

Frank Grunthaner

[FrankGRUN]

Installed the bolt hole adapter. It uses the four 1/4-20 bolts at the corners of the new 9430D715 ceiling assembly and just two of the three 3/8-16 bolts to the older 6749R707 air conditioner internal base plate. I used L-section aluminum, 0.250 inches thick and 1" long on each side. After studying the original installation material for the rooftop AC, I realized that the heavy metal ceiling assembly of the old unit provided the sealing compression for the roof seals as the three internal bolts were tightened. The new bolt adapter bolts firmly (metal to metal) to the original AC internal base plate. Coupled to the metal adapter of the 9430D715 assembly, the new structure provides more compressive force and does so symmetrically about the 14" x 14" ceiling opening.

Now to the electronics. Studying the wiring diagram for the 9430D715, I found that it supports a two speed fan motor, while my older 6749R707 AC system has only a single speed fan. I also find that this is a single phase motor with capacitor in the circuit while running. As a result, I'm looking into a trial circuit to select a single lower speed that won't result in condenser freeze. If anyone knows what the two fan speeds are in the current crop of Coleman RV AC units, I'd love to learn the values.

Frank Grunthaner

[FrankGRUN]

Another Progress Update! I have uploaded several pictures of the bolt adapter installed. In the first, you can see the squirrel cage fan that draws cold air from the evaporator and pushes into the ceiling assembly. I have not yet supplied the photo with the duct interface showing old and new approaches melded. Another photo shows the crossbar and its relationship to the air outlet and the warm air return. The heating strip mounts up in this larger area. The last photo captures the full view of the two beams that capture the four mounting bolts from the new 14 x 14" adapter around the ceiling opening. It also shows the 1/4-20 bolts going to the beams, and the 3/8-16 bolts that fasten the assembly to the older AC base. The distance from the bottom of the cross-brace to the top of the welded 3/8-16 nut in the older AC base plate is 1.25 inches. For this photo, I have used a stack of steel washers and a 1/2" nylon spacer to give a solid 1" diameter support to each of the two 3/8-16 bolts. The crossbar is bolted to the two rails with 1/4-20 flange bolts and nuts.

I have tested my triac circuit and it works perfectly. My best information is that the two speeds in the later Coleman motor are 1625 and 1050 rpm, corresponding to 300 cfm and 200 cfm. I will adjust the triac circuit to these values with an airflow meter upon final assembly . At full speed the existing motor draws 3.05 AC amps and 4.02 amps at the slowest setting I can generate (60VAC) with the triac. The triac speed control box is to be mounted to the crossbar.

If one looks closely at the last photo, you can make out a blue and a green wire stapled to the outside of the ceiling cutout. This was a pleasant surprise from Born Free, in that this is 12VDC which I will use for an LED light (460 lumens) that I will mount to the 9430D715 ceiling shroud. The LED light is 3" in diameter and just 1/4" thick. I will mount the on/off switch in the Coleman LOGO.

The last project is implementing the AutoFan from AirSwitchRV.com.

[Excell]

Nice Job very interesting .

[bruceisla]

Nice work Frank! Looks good so far !

[FrankGRUN]

This is my final progress update! The 9430D715 Ceiling Assembly update and upgrade of the 1982 Coleman AC and ceiling assembly is complete and functioning perfectly. I have uploaded several pictures showing some of the detail. In addition to fabricating a simple bolt hole adaptor to bring the old AC base plate mounting system to interface with the new mounting adapter of the post 2002 RV AC assemblies, I added circuit modifications to change the single speed fan to a two speed capability, added the AutoFan capability provided by AirswitchRV and a center-mounted LED cluster for illuminating the kitchen area. I also added several override switches to disable the low speed circuit or the AutoFan should an unforeseen crisis require such intervention.

For the help of others who are interested in this approach, a few comments are in order!

First, on the bolt adapter. I used 1/4" thick aluminum 1" wide angle for strength and rigidity. Both have proven well. The original ceiling assembly used three 3/8-16 bolts that fixed the thin sheet metal box (contained the controls, heat strip and air flow deflector) to the RV ceiling. My adapter uses the center two of these. This presumably also provided the hold down points for the AC unit and compressed the weather seal at the base of the AC on the RV roof. The new design of mounting adapter (supplied with the 9430D715) affixes to the 14 x 14" cut in the RV ceiling and uses 4 corner bolts to fasten it to the rooftop AC. I was originally concerned about the symmetry difference between old and new mounting. Also, it was quickly apparent that one of the three original bolt points could not be used with the new air duct design. So I designed the adapter to be sufficiently rigid as not to permit any flexing of the rails relative to the crossbar that bolts to the original AC base pan. I also fabricated a set of spacers between the crossbar and the 3/8-16 bolt receptors that contacted the AC base plate and had a full 1.5" diameter contact to minimize any bolt point flexing to the AC base pan. As a result, the new adapter combo uniformly drew down the rooftop AC to ceiling surface such that the original gasket material compressed by the same amount +/- 0.25 mm after installation. I have uploaded two different views of the adapter so it can be more easily visualized (See Coleman bolt hole ...).

Second, I wanted to fully implement the heat strip. The old heat strip was a wire wound about a series of loose insulator segments and was located inside the sheet metal air box. I used the Coleman heating element 9233A4551 which fit perfectly in the AC return airflow channel. This is specifically not the element recommended by Coleman distributors for the 9430D715.

Third, inspecting the wiring diagram for the 9430D715, I quickly discovered that it was wired for a 2-speed fan motor. It turns out that all Coleman 13,500 BTU AC units made in recorded history (for Coleman this seems to start around 1995) had two speed fan motors. My unit (model 6749R707) had a single speed fan motor. Further, heater function of the 9430D715 used a low speed fan and I would later realize, the low speed fan was significantly quieter than the high speed version. With some research, I found that my original single speed fan operated at 1625 rpm and was a capacitor-run motor. In other words, it has a capacitor connected across the motor windings at all times. This permanent split capacitor motor (PSC) is very efficient and is easily speed controlled with a simple Triac semiconductor circuit which essentially reduces the AC voltage supplied to control motor rpm. The newer Coleman AC units use a two speed motor with 1625 rpm high speed and 1050 rpm low speed windings. Since the airflow (cfm) of a squirrel cage blower fan in a given enclosure is a linear function of motor rpm, I deduced that if the high speed fan airflow was quoted as 320 cfm (existing Coleman AC literature), then the low speed was 206 cfm. I wired in a triac speed control ($14, Amazon, shipped) and after assembly, adjusted the measured air flow at my low speed setting to 62% of the high speed value using a handheld anemometer. The dissipated power consumed by the fan at this lower speed is just about 73% of the full speed power so there might be a 10-20% reduction in efficiency using the triac for a speed control.

Fourth, I added appropriate wiring modifications to the circuit powering the fan in the Low Cool and High Cool modes to let the fan only switch on when the AC compressor is powered. The components are marketed as the AutoFan by AirwsitchRV. I also brought out override switches to the outside of the AirFlow channel for easy access should I need to defeat either the speed control or the Autofan. AutoFan mode functions perfectly. I have uploaded two photos of the plastic airflow baffle and control box assembly showing the override switch locations. To minimize airflow disruption, the wires supporting the switches are brought out from the control box through a sealed grommet and fixed to the surface with adhesive foil tape.

Fifth, the biggest change needed converting old to new was in the mounting of the fabric duct adapter to the old AC base plate and outlet.The old cold air outlet was through a 4.5 x 5.25" square outlet, while the new duct coupled to an opening closer to 4.5 by 8". I briefly considered opening the AC base pan to conform to the new duct assembly, but soon realized that the squirrel cage blower fan shroud had been carefully mounted to the base pan. Airflow in these centripetal blower fans is a complex function of the shroud design so I chose not to modify the opening in the base pan. To interface the new duct to the old pan and keep the three screw interior hold down approach, two things were required. I had to remove the 3/8-16 bolt mount point at the edge of the air outlet. Your trusty Dremel Tool is your friend in these situations! I also had to cut off 1/2" of the projecting plastic tab on one side of the new duct plastic collar. This left enough of a ridge to capture with a sheet metal screw. The two plastic tabs and holes on the other side of the duct collar were left intact. Positioning the duct collar against the AC base, I drilled three holes for 3/8 inch long #6 sheet metal screws and secured the collar. After drilling the holes (cautiously - not knowing what was above on the single hole side) I probed for internal clearance and found a minimum of 1/2" clearance to any component above. I then sealed the collar to the AC base with non-drying, non-oily plumbers putty as one can see in the picture labeled plumbers putty. I've also uploaded a photo of the ceiling assembly fully mounted showing the fabric duct before trimming and sealing to the channel adhesive. For efficiency, the most important consideration is sealing the cool air outlet and airflow path from the return air inlet. The new ceiling assembly does a far better job of this than the older design.

Sixth, I have always felt that Born Free didn't have enough lighting in the kitchen area, specifically in the hall about the refrigerator, oven, counter and sink. Staring at the flat surface of the 9430D715 ceiling assembly, I decided to add a thin LED 12V puck light to that outer surface. I chose a warm white 180 lumen light that draws 0.25 amps when fully illuminated. I added a mini toggle switch in the Coleman control box and centered the switch in some of the Coleman graphics. The presence of 12VDC at the AC 14 x 14" hole really simplified the job.

I have enclosed a photo of the final ceiling assembly with the light illuminated and a closeup of the Coleman controls, LED and mini toggle. These pictures show the next project - replacing the ceiling vinyl covering. In the Born Free, this ceiling covering is only in the kitchen and bath area and the problem zone is most likely due to an early rain leak about the AC seal. Any suggestions will be greatly appreciated!

My apologies for the detail and length, but its an old habit, hard to break! Hope this helps someone else...

Frank Grunthaner

[FrankGRUN]

Pictures didn't make it in the last post. Hopefully these will pass through!

[Deano56]

does anyone make a auto fan for the Dometic?

[FrankGRUN]

I haven't looked at the Dometic wiring of the fan and compressor but I would think the same approach would work. A quick query to AirswitchRV.com should get a definitive answer.

[JohnRR]

That's a mighty fine upgrade and thorough step by step accounting of the change over.

Thank you for sharing.

[bargeman]

Nice upgrade!

[FrankGRUN]

Thanks much! I'm really happy with how it turned out. The new ceiling assembly is much quieter and the "two speed" fan is really efficient on the heat setting. It also seems as the new heater strip is also much more effective.