Anyone add the third air conditioner to Fuzion 420?

[twvette]

Curious if it is likely "pre-wired" for the third AC? I have one in the front bedroom and the other is in the garage. I have two very basic thermostats for these so not sure how would "control" the three also as assume get to only use two at once. I see the location for the third was above the bunk bed where currently have a roof vent. Seems like a bit strange location so not sure how effective it is, especially since also don't know if might be some plugged ducting to tap into also to help get it from the bunk area out into the actual living area or if will just have to be a direct dump of air only?

[ChuckS]

You will need the power management module amongst many things before you can add in a third AC unit...

Does the “pre wired” option already incorporate this....

https://www.trekwood.com/products/57...re-For-3rd-A-C

[chuckster57]

Is there another breaker in the panel or an empty slot labeled? 3 AC’s would need 3 separate breakers. Is there a plate at the vent? You can remove the trim ring and look for 110VAC Romex and maybe 5 strand thermostat wiring or 12VDC wiring.

If you don’t have all the above, your probably not prewired for a 3rd AC.

[K_N_L]

Our unit was prewired at the rear vent but - it was connected to a load sharing switch to split service between the front bedroom and the garage. I didn’t like that and opted to install a new breaker. The load sharing device was close to service panel so it was a short re-wiring job. There was no thermostat wiring so that was a bit of a challenge to link back to the central unit via the ducting. As Chuck noted the trim ring will reveal all. Likely both 110 ac and 12v dc for a fan is pre-staged. Good luck!

[infantryofficer81]

Our 420 came with 3 AC units installed. One's located in the bedroom, one in the bunk bed area, and the 3rd in the garage. I can have all three AC units on, but only two will run simultaneously. It will function the same whether running on the generator or shore power. We have one thermostat on ours that shows 3 zones. I will note that it gets cold as ice in that bunk area! I don't understand why Keystone put the AC unit there and not in the living area. I've found if I close the vents on that unit, it makes a tremendous difference (increase) in the amount of air flow coming from the vents in the living/kitchen area. Sorry, I couldn't be of more help.

[Jbbooks]

Originally Posted by infantryofficer81

Our 420 came with 3 AC units installed. One's located in the bedroom, one in the bunk bed area, and the 3rd in the garage. I can have all three AC units on, but only two will run simultaneously. It will function the same whether running on the generator or shore power. We have one thermostat on ours that shows 3 zones. I will note that it gets cold as ice in that bunk area! I don't understand why Keystone put the AC unit there and not in the living area. I've found if I close the vents on that unit, it makes a tremendous difference (increase) in the amount of air flow coming from the vents in the living/kitchen area. Sorry, I couldn't be of more help.

I have a 371 Fuzion with three AC units. The third AC is in the den/kitchen offset to the driver side of the room, not in the bunk area. It has a separate thermostat mounted above the fire place. It also has a separate electrical 30 amp hook up outside for the AC. So I have the 50amp cord and if I want to run 3 ACs a 30 amp cord for the den/kitchen AC. Not sure if this was factory or dealer installed, but all thermostats and ACs look the same. I have the arctic insulation package and three ACs will keep the trailer cold even in the hot Texas sun.

[LewisB]

Originally Posted by ChuckS

You will need the power management module amongst many things before you can add in a third AC unit...

Does the “pre wired” option already incorporate this....

https://www.trekwood.com/products/57...re-For-3rd-A-C

Actually, that's exactly what you DON"T want if you want to run all 3 AC units at the same time (on a 50A service). Keystone often uses this "Power Share" switch to reduce the electric load by only allowing only 2 of 3 AC units to run at one time. However, with a 50A service and the AC units wired to individual breakers in the WFCO power panel, it is quite possible to run all 3 units simultaneously and you DON"T want to use the power share switch.

If you are suffering in the heat, have 50A AC service and want to run 3 AC units, it is very possible. See:
https://www.keystoneforums.com/forum...ad.php?t=39365

Also check out post #6. Here's a case where a second AC service was added to the trailer specifically to run the 3rd AC unit. This is also a workable option.

[JRTJH]

Originally Posted by LewisB

Actually, ...

Also check out post #6. Here's a case where a second AC service was added to the trailer specifically to run the 3rd AC unit. This is also a workable option.

The problem with wiring a trailer like is described in post #6 is not the wiring, but the campground power grid. Quite often, the 30 amp plug on the campground power pole is wired to one (or the other) of the 50 amp legs. Supposedly, every other power pole is wired to the opposite leg. That doesn't always happen, and in many campgrounds, one leg of the campground grid is overloaded while the other leg doesn't see much load.

What happens is "even most careful big rig owners" will plug in the 50 amp cord (often with an EMS in the system) then they will plug in that 30 amp cord to the power pole 30 amp connection (often without an EMS)...

If the 30 amp campground plug is "wired off the 50 amp plug" then there is a likely chance that running all three A/C units will draw down the power, cause a "brown-out condition" and as the voltage goes down, the amperage draw goes up. Without an EMS on the 30 amp power cord, that A/C is not being protected by the 50 amp EMS in the trailer.....

If there is a "lack of thought" in laying out the campground power grid and all or most (even all or many) of the 30 amp plugs are wired to the same leg of the 50 amp system, with other campers using that side of the grid, the "brown-out condition" can be even more problematic.

Anyone who uses a "doubled up trailer electrical connection" (a 50 amp and a 30 amp or even a 30 amp and a 20 amp) without using a "doubled up EMS protection system" is only "partly protected" from electrical problems that tend to be more problematic in some campgrounds, especially those with older electrical grids that were upgraded to 50 amp plugs after the grid was installed.

[LewisB]

^^^I absolutely agree with John's comments in the previous post. EVERY electrical connection to your RV should be protected by an EMS. So multiple connections require multiple EMS systems.

In most cases, using multiple AC connections (as in post #6) ends up being more expensive and requires more equipment and work to set up at each use. There is plenty of power available in the 50A RV service to run 3 AC units and everything else you want. So wire it up correctly the first time - you will be happy you did!

[ChuckS]

The initial current surge is going to exceed 50 amp service sooner or later at some point with two units running and a third kicking in... the standard OEM RV power cable plug ends... let alone the overall size of the cable wiring would be marginal at best without a power management device...

might get away with it for a while without power management but the cord and plug ends are gonna be hot

[JRTJH]

Originally Posted by ChuckS

The initial current surge is going to exceed 50 amp service sooner or later at some point with two units running and a third kicking in... the standard OEM RV power cable plug ends... let alone the overall size of the cable wiring would be marginal at best without a power management device...

might get away with it for a while without power management but the cord and plug ends are gonna be hot

First, EVERY trailer should have an EMS installed and IMHO, it should become a factory standard item, just like the water heater, microwave and furnace.

That said, I'm not sure I completely agree with the bolded statement. A 30 amp trailer provides 3600 watts of power on a single buss with a 20 amp breaker (2400 watts) for the air conditioner circuit.

A 50 amp RV provides two 50 amp busses, each capable of 50 amps (6000 watts) wiring two 20 amp breakers on one buss (4800 watts) and one 20 amp breaker (2400 watts) on the opposing buss would spread the power draw and wouldn't put the system in overload. Hypothetically, if all three A/C's started at the same time (2400x3) the maximum draw could be 7200 watts, still well below the 12,000 watt total available power.

Dometic's power requirements for generator sizing requires a 5500 watt generator to power 2 air conditioner units (500 watts below the 6000 watts available on one 50 amp leg).

Granted there "may be a start surge" that could "conceivably" cause a momentary overload, but the chances of that random start condition occurring is extremely infrequent. In the event it did occur, the circuit breakers on the double leg would open to protect the circuits from overload.

With an EMS in the RV, even that condition would be "protected by the EMS".

I would suggest that if an owner plans to regularly operate both A/C units that are wired to the same leg on the buss, then nothing else should be wired to that buss (that would also be regularly operated at the same time). If electric supplemental heat (in the furnace system) were to be considered, then wiring it to that side of the power distribution panel would be OK, since the A/C's and the furnace would not be operated at the same time...

I'd recommend, in that case, to use one leg of the power panel for HVAC and the other leg for "the rest of the trailer plus the "3rd A/C unit"...

As you said, with an EMS in the system, the trailer would be protected from the "low voltage" possibility if the circuit breakers did not open in the extremely rare situation where both A/C's on one leg might call for a compressor start at the same instant...

The problem, as I see it, is a campground grid that suffers from frequent overload and subjects the trailer (any trailer) to low voltage... That, coupled with three A/C's in a 50 amp trailer, without an EMS, is a "sure way to have electrical problems"... Sooner rather than later.... The same situation would occur, even with a 30 amp trailer and one air conditioner, not because of inadequate wiring or trailer capacity, but because of the low voltage condition that results from inadequate campground grid.

[LewisB]

Right on point! When wired correctly, the weak link will be the campground service. The 3 AC units and other higher power equipment likely to run together need to be split on the 50A RV service to spread the demand to both halves of the distribution system. Here's an in use snapshot of power draw with 1 AC unit on the top (left) leg and 2 AC units and the battery charger running on the lower (right) leg of the distribution. The AC units pull 13A each and the converter was pulling about 5A. There is nothing here that would cause "hot" plugs or trip breakers. This photo was taken in Tucson with the outside temperature at 109°F and inside temperature at 72°F.

3 AC units running simultaneously is the best modification I have ever made to our rig!