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Old 07-24-2016, 10:51 AM   #1
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Replace Coleman Mach 8 AC Unit

So after only 1.5 seasons (which admittedly are long and brutal in South Louisiana) our rear Coleman Mach 8 15K BTU air conditioner died. The compressor locked up.

After a lot of hemming and hawing about how to move forward, I decided to replace the unit with a Coleman Mach 15 (also 15K BTU).

The new Coleman would have several drawbacks:

1. Doesn't fit "exactly" the same
2. May or may not work with the existing wiring, thermostat and control module
3. Adds an additional few inches to the already very high profile of the Trilogy.

The pros outweighed the cons for me:

1. Longer track record of durability
2. To say much quieter is an understatement. (Inside and outside)
3. Less expensive to replace
4. Better cooling power

I wanted to share that I was able to throw the old unit off of the roof and drag the new unit up the ladder and install it in about 1 hour. I say "install" loosely because technically it's not even bolted down as I wait on a mounting bracket to arrive that I will have to place below the unit in a new hole in the ceiling. It's not a tough job and will take about 15 to 30 mins to complete. I will have to add new trim to clean up the look from the inside.

In the end I wanted others to know that it is possible to swap the Mach 8 with a Mach 15 with no major issues. In my experience the quieter operating is the single biggest advantage. My wife actually had to get up in the night to go check it because she thought it wasn't running. It's that quiet.

I also wanted to note that there is a potentially huge loss of cooling power with the original install as Dynamax saw fit to just throw the gigantic control module box right down into the intake area of the 14" x 14" AC hole in the ceiling which consequently disrupts airflow significantly and blocks I would estimate about 30% or more of the airflow into the AC unit.

The solution is to move the control box up into the AC unit and screw it down. It won't block the airflow near as much and will greatly assist the unit's ability to cool. This can be done on the Mach 15 but there is no room to move that control box up into the AC unit in the original Mach 8. I believe this is the source of a huge loss in cooling in the Trilogy models.

I am including a photo of the control box in the intake for reference.

If you need to replace an AC and want quieter operation and better cooling AND can deal with a minor modification to the mount procedure as well as a few more inches in height then I would greatly recommend the Mach 15.

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Old 07-24-2016, 08:52 PM   #2
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Just out of curiosity, did you contact Coleman about your failure? It would seem the Coleman warranty would be longer than one year on the compressor.

How is the weight of the Mach 15 compared to the Mach 8? Is the Mach 15 a high performance unit?

I have had failures on two of my three AC units. In one, the fan (squirrel cage) threw some blades out and sounded like an explosion. The other had a cooling fan inside the unit on the roof come apart and caused minor damage, but locked up the unit. In both instances, I contacted Airxcel and they sent replacement parts, free of charge. Great service from them. The Forest River warranty had expired.

John
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Old 07-25-2016, 06:37 AM   #3
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So, sounds like the low profile Dometic units sound like our Coleman (especially the one in the bedroom). The gents at Dynamax checked it out to make certain it wasn't loose, but it vibrates and sounds like it is ready for take-off!


God Bless,
David & Cathy

2015 Trilogy 38FL
2016 Silverado 3500HD DRW
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Old 07-25-2016, 07:00 AM   #4
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In 106 I wasn't going to be able to wait on any replacement parts. The mission was to find a solution and as fast as possible.

The compressor is non-replaceable--considered a non-serviceable part anyway. If it goes, you replace the unit.

Airxcel would probably have warrantied the unit. To what extent I do not know, but then again I wasn't really very interested in another Mach 8. To me they do not have a good track record.

The Mach 15 is HIGHER performance than the Mach 8. It has larger coils (condenser and evaporator) and moves more CFM than the Mach 8. With just the front Mach 8 and the rear Mach 15, our camper is now staying 75 all day long even in direct South Louisiana sun all day at very high temperature and humidity levels. That blows my mind.

At this time of year, I walk out from the camper during the day and it's like walking into a gigantic sauna and water begins to condense on my skin. Yucky!

So, all around perhaps I spent some money that--given enough time in the heat and willingness to stay with the Mach 8 under warranty--I may not have HAD to spend. In the end I am much much happier with the result.

Can I mention again how much quieter this thing is? Gee whiz, it's like it isn't even there--except that it would be untenable in the camper without it! I find myself anticipating the failure of the unit in our bedroom,
just so that I can enjoy the quieter operation!


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Old 07-25-2016, 08:48 AM   #5
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Okay, post coffee and morning walk, I get it! Dometic was never in the conversation....AirXcell all the way.

So, kwoodrg, roger that about the Mach 15 vs the 8. Question, are you running 2 or 3 units? And the Mach 8 was in the bedroom, correct?

I took our rig up to Dynamax for the warranty work and then to MorRyde. They are beginning the removal of the OE, then installing the IS w/Kodiak disc system, tomorrow.

Five outstanding items on my list:
Clean, condition and protect newly painted front cap with Reflex
Solve for the best HVAC solution (performance/noise reduction)
Install insulation to reflect the heat back out of front cap and bedroom
Install internal electrical and surge protection
Install sewer hose compartment underneath the bedroom (already have the components so this will move up the list)

We are planning a late spring trip to the west. I want the HVAC in tip top shape by then. Cathy is very sensitive about "being warm when she is sleeping". Researching the options now and wide open to recommendations.



God Bless,
David & Cathy

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Old 07-25-2016, 05:29 PM   #6
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For those that are saying their ac unit is loud, have you replaced the fan blade with the 3 blade fan? Ours originally had 5 or 6 blades and I did a search and learned that if you replace those with the 3 blade fan it is much quieter. We have 3 Coleman Mach 8 low profile 15k units and I replaced all 3 fan blades and they are much quieter. Total cost was about $50.
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Old 07-25-2016, 10:34 PM   #7
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David our rig is running two AC units. Dynamax didn't offer a pre-plumbed location for a third AC in the bunkhouse model until the 2015 model. Ours is a 2014. At 42.5 feet, two ACs on the 37BH model is definitely the bare minimum required to adequately cool the trailer.

Our rig came with two of the Coleman Mach 8 15,000 BTU units. They are super loud and the vibration from the compressor is not dampened adequately in the design of those units. After pulling it apart and looking at it's design vs the Mach 15 I installed this past weekend, I think a key factor is that the compressor is mounted at an angle that transmits the vibration downward into the camper because of the centrifugal force.

The Mach 15 has the compressor mounted upright, so the outward centrifugal force of the compressor is thrown out laterally which the rubber seal absorbs effectively without really affecting the camper. Of course I am no mechanical engineer, but that seems to be what is happening.

Then there is the blower noise which is heard inside and outside on the Mach 8 units. The blower outside is so loud that with two Mach 8 AC units running, you could hear our camper over top of every other camper within about 100 ft. Those vertical blowers are very loud. This is undoubtedly because they had to use smaller fans at a higher RPM to evacuate heat up away from the coils in the smaller space inside the Mach 8.

The Mach 15 uses a larger fan that runs at a lower RPM yet because of the fan size and larger coils it moves more air and removes more heat. Anyone with experience in cooling anything knows that the smaller the blades of a fan, the higher the RPM required to move the same amount of air.

As thumper mentioned you can replace the outer evaporator blower fan to reduce some of the noise, but the removal of blades reduces the air movement capacity. This may work in more moderate environments, but here in south Louisiana it would kill even more cooling capability that we cannot afford in extreme conditions such as where we live. The Mach 8 needs all the help it can get moving heat out off of those evaporator coils in this extreme humidity. Also, reducing that blower fan noise outside won't help the jarring noise and vibration of the angle mounted compressor in the Mach 8.

AirXcel says the Mach 15 is specifically designed for high demand and high humidity environments.

What I can say at this point is that a few days into running a Mach 15 in the rear of the trailer and comparing that to the factory Mach 8 that still is in the bedroom up front, it is night and day difference in terms of noise. The Mach 15 is an order of magnitude quieter. I would also rate the cooling to be around 10% better on the Mach 15. At this point when the front (bedroom) Mach 8 fails, I will most definitely swap to a Mach 15.

In the end it's not something I would do if the existing factory Mach 8 units were still running okay, but it's a no brainer if you have to replace a unit anyway. Just be cautious of the additional few inches it adds to your camper profile. Also bear in mind that we don't pull our camper super often and I'm told higher profile AC units can take an extra mpg off your towing fuel efficiency.
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Old 07-25-2016, 10:44 PM   #8
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kwoodrg,

Could you provide more information on the mounting bracket that you had to wait on? Where did you get it, cost, part number, etc...

Also, can you elaborate more on your comments:

I say "install" loosely because technically it's not even bolted down as I wait on a mounting bracket to arrive that I will have to place below the unit in a new hole in the ceiling. It's not a tough job and will take about 15 to 30 mins to complete.

You had to cut a new hole???

John
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Old 07-25-2016, 10:56 PM   #9
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I just managed to find a bracket today. A local RV shop had a few lying around and gave me one for free. From what I can tell there is no separate part number. Generally it come with a full ceiling assembly kit. I don't want or need the full kit since I am going to mount the AC to the mount plate from inside and place a trim piece of wood over the hole and seal it up. This will also give me convenient interior access to the AC wiring and control box from inside in the future.
So, my new Mach 15 is not bolted down yet at all. I needed that bracket to mount it properly (and probably the way the original Mach 8 should have been mounted anyway) from the inside.

Dynamax put lag bolts right through the bottom of the old AC's plastic base right into the roof.

AirXcel doesn't mention anything about that being a legitimate method of mounting the Mach 8 and I'm not even going to think about drilling holes through the base of the new Mach 15 and into my roof like what was done the original Mach 8. I have no doubt those bolts going straight into the roof also a apart of the noise/vibration issue.

When I'm done (this weekend) I'll have a few more pics to share. Last weekend was just a mad scramble to get cool air flowing again. :-)
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Old 07-26-2016, 08:31 AM   #10
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I'm going to go back to my thought detour and ask, why not Dometic? I can understand why Dynamax made the change, they are 10% cheaper. Though it seems users/owners rate them very high, and AirXcell units loud and less productive.

We are not going to rush out and replace our existing units. Safe bet is when they fail, we will upgrade to the better unit.

Chill out ya'll!


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David & Cathy

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