Rooftop AC Unit Replacement

[Mbiallas]

Well we have thrown in the towel on our old Coleman Mach unit. After reading a few articles it would appear that replacing the unit will not be all the difficult. From what I understand it basically involves unbolting the old unit and disconnecting the power wires and the wires from the thermostat and then reconnecting in reverse order.

Well that all sounds simple enough, but I would really like to hear from some other ordinary Joe's that have actually done this. Most of the videos I have seen are for non-ducted units. Ours is ducted. I doubt this would make much difference in installation but figured I would ask. Please let me know what your experience was like.

[j-d]

I can only answer part of this.

A motor costs $100 on Amazon and isn't that hard to change. The blower wheel cleaning I did, was part of a motor replacement job. I can usually salvage a motor if it's a bearing problem, but I could not keep our old one running. It'd run free then stick. That was after dismantling, cleaning, crocus-clothing, lubricating and ... and ... I still have the old motor and all it needs is a new set of sleeve bearings with new wicking to keep the oil around them.

A 15000 does noticeably more than a 13500. Problem is, it takes a 30-amp coach right to the limits of its 30-amp pedestal service. When we had a 13500, we could run our 24-ft C in "total electric" mode. We could cool air, heat water, make coffee, even microwave, with the converter running. With the current 31, we heat water with LPG, only use one plug-in appliance (toaster, coffee maker) at a time, none with the microwave, and sometimes the main breaker will trip if we microwave with the A/C running.

I like to salvage things, restore to running condition, but I believe that if an RV A/C has a refrigerant leak OR needs a compressor, it's time to replace. I was shopping and reading reviews awhile ago, and to me, the "Coleman" (RV Products) is still the best bet.

Both of our Mach units have been non-ducted with no wall thermostat. As such they had very few "controls", just On/Off/Fan Speed Knob, and Analog Thermostat Knob. So I can't help with the control aspect. Fortunately we have some very good techs who can help you with that. I believe the Coleman website has info about replacing an older Coleman with a new one.

[wa8yxm]

Unit weights soemthing like 75 or 90 pounds, Forget which.. Just did the job here but was replacing a different make with a coleman

Remove inside grill
Disconnect upper unit from lower unit (Wires, all plug in I think one plug but might be 2) you may need to disconnect a ground lead (one screw)

Remove 4 bolts

Remove rooftop unit, clean mounting area, optional replace gasket (I would suggest you do this, it just sits there, like a throw rug)

Position new upper unit,, This is a 2 person job, only one needs muscles. (One on roof one inside)

Insert 4 long bolts and run down, DO NOT TIGHTEN AT THIS TIME initially.

now evenly tighten the 4 bolts till the indicator (RTFM for location of indicator) indicates proper amount of compression.

Plug plug in
Test
replace ceiling grill and filters.

Tools needed

Screwdriver matching screws holding up ceiling grill (#2 Phillips normally or #2 Square as the option, #20 Torex in my case today)

Wrench Forget size, for long bolts.

Suggestion.. Reversible power drill with adapter and socket for removing those long bolts.. Lots and lots of turns.. How I did it.

[Mbiallas]

j-d wrote:

Mbiallas wrote:
Well we have thrown in the towel on our old Coleman Mach unit.

Does the Old Mach still run? We were about to sell a 24 year old Class C with a 13500 Mach on it, just to sell it. Came across Chris Bryant's article on how to clean the coils and drain. Did that, and it got its cool back.

We bought another C with a Mach 15000 on it, cleaned the coils as Chris explained in the article, also pulled the motor and cleaned the indoor blower wheel (squirrel cage). That Mach is now 15 years old.

One thing I learned recently, again Shout Out to Chris, is that the back of the unit, the condenser coil, has to have its edges sealed to the shroud with air baffles. A little hard to explain, but the air over the condenser is drawn in from behind. It can't be allowed to get some of that air from the side vents of the shroud. Easy fix with some foam insulation for copper pipe.

We have cleaned the coils and they look great on both sides. I'm afraid the motor is nearly shot as I often have to climb on the roof and give it a hand starting while someone else hits the switch inside. I had hoped it was the capacitors but they were all replaced a few uses ago. As I understand the fan is supposed to pretty much free-spin when you touch it. Ours is tough to spin and most certainly stops dead as soon as you quit pushing it along. And now the compressor doesn't want to kick on at all.

We had planned on getting a new thermostat as well as a new unit. The current unit simply has a grate on the ceiling that holds the air filter and gives access to the wiring. Is there anything else we will need to purchase aside from the unit and thermostat? I read somewhere that there was some control module (not sure if that is the right name) that was needed but didn't come with the new unit. That person said they were able to pull it from their existing unit and it worked on the new one.

Also - will there be a noticeable difference between a 13.5k and 15k btu unit? Our camper is a 37 footer located in South GA. So we need all the cooling we can get.

[jvowell1]

I did mine this past summer. Used a extension ladder stretched out and slid the unit in the box up the ladder by pulling with a rope. I'm 64 and did it myself.

[j-d]

Mbiallas wrote:
Well we have thrown in the towel on our old Coleman Mach unit.

Does the Old Mach still run? We were about to sell a 24 year old Class C with a 13500 Mach on it, just to sell it. Came across Chris Bryant's article on how to clean the coils and drain. Did that, and it got its cool back.

We bought another C with a Mach 15000 on it, cleaned the coils as Chris explained in the article, also pulled the motor and cleaned the indoor blower wheel (squirrel cage). That Mach is now 15 years old.

One thing I learned recently, again Shout Out to Chris, is that the back of the unit, the condenser coil, has to have its edges sealed to the shroud with air baffles. A little hard to explain, but the air over the condenser is drawn in from behind. It can't be allowed to get some of that air from the side vents of the shroud. Easy fix with some foam insulation for copper pipe.

[rhagfo]

Chris Bryant wrote:
It can be a bit of a pain to get the new unit well sealed to ductwork- usually the old one will have a more compressed gasket, so the baffle will not adequately seal.

LOL! I spent an hour with aluminum duct tape sealing my factory job one day, likely the new install will be better.

[Chris_Bryant]

It can be a bit of a pain to get the new unit well sealed to ductwork- usually the old one will have a more compressed gasket, so the baffle will not adequately seal.

[wrgrs50s]

The hardest part is getting the new one on the roof. They are heavy and awkward.

I used the bucket on my tractor, but seen a video of 2 guys using a rope and a ladder sliding it up (still in the box). Guy on the roof kept it stable holding the rope and pulling and the guy on the ground pushed from underneath while going up the ladder.

The rest is a piece of cake just like you figured.

[Johno02]

Unless you have a few more good folks to help, I would be very cautious about doing it yourself. The units are quite heavy, and can do a lot of damage to your roof if not handled carefully.