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Old 01-16-2015, 11:21 AM   #1
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Onan 5500KW Quietdiesel Issue

I'm trying to help one of my traveling friends with an issue they're having with their DP. They have a 2007 Coachmen Sportscoach Cross Country with an Onan 5500 Quietdiesel. I have a similar coach but mine is the Pathfinder series and I have the 7500 Onan. Their problem is they cannot run both ACs at the same time. I can't believe a manufacturer would build a coach with a generator that's too small. This is a 50 amp DP. When they try and run both ACs, they will run for a while. Sometimes hours. Then, the generator will bog down and die unless they shut one down. Occasionally, it has tripped one of the breakers on the generator. I'm pretty sure both AC units are Dometic 13,500 BTU units. When mine is on generator, I have no problem running both ACs, electric water heater, microwave, etc.

When they are plugged into shore power, there are no issues. Also, the coach has no power management as mine does.

I'm not sure if one of the ACs has some sort of issue or it's generator related. Any ideas would be appreciated. We are heading out on a long trip out west later this year and they're going to need both ACs running down the road.
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Old 01-16-2015, 02:27 PM   #2
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We have 2 13500 units on a gas 5500 and we had a similar problem. It was lack of fuel. Maybe they need their filters or fuel pump changed. Although ours is gas the lack of fuel produced the same symptoms. Ours would bog down and shut off due to underspeed. That was running in 98 degrees on a blacktop parking lot while tailgating so they had to be pulling pretty good amperage. Replaced fuel pump and next game under the same conditions it ran for 12 hours with no problem.


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Old 01-16-2015, 04:37 PM   #3
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In an ideal situation the 5500 generator will produce 5500 watt/120 volt=~46 amps. Depending on temperature and elevation it will produce less, I would assume 40 amps available.

Both my AC's will pull ~13 amps each, plus the refrigerator in the will pull ~4 amp, plus Water heater 10 amps, battery charger ~2 to 7 amp. At this point generator is overloaded. Add lights, coffee maker, microwave and your in trouble.

I would guess that if your friends are not aware of their consumption they could easily overload the generator.

Yes it is hard to believe a manufacturer would put a small generator like this in a rig but that's how they can compete and market their product.
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Old 01-16-2015, 05:35 PM   #4
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Jacwjames has it right. It is the surge that gets you. It may run ok for a while because the ac's, fridge, water heater, and any other thing using power are not all starting and pulling high amps at the same time. All it takes is for the fridge to be running, the water heater to start up and the ac's to try to kick in about the same time and, boom, you are over the limit.
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Old 01-16-2015, 05:44 PM   #5
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Yeah, I don't think that's it. They don't run the electric water heater and many times it's happened in the middle of the night with only the AC and fridge running.
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Old 01-16-2015, 09:23 PM   #6
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It may be more of an a/c problem than generator problem. He should check the start and run capacitors. Possibly one of the a/c units has some kind of starting issues
My Onan 5500 will run both a/c's and the refrigerator all day long in 98 degree weather
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Old 01-16-2015, 09:42 PM   #7
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Something is definitely wrong... the a/c units are likely on on 20 amp circuits -- so if they are the only things running you should have no issues. Heck, I've run 2 a/c on 30 amps many times (just making sure fridge and water heater were on gas). If the generator is bogging before shutting down...that sounds wrong. Filters and then injectors could be culprits.

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Old 01-16-2015, 09:52 PM   #8
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Watts divided by volts = amps. 5500 / 120 = 45.83 amps at maximum performance, under 500' elevation. (Louisville 466') If you go to central Kansas or the Appalachian Mtns. you're at over 2500' and your generator is down to 5170 w or 43 amps. By Denver 5280' or so, the generator at max. is putting out 4675 w. (38 amps) That is maximum performance, clean filters, etc.

With all that, the generator should handle two A/C's without effort, unless, as said above the starting effort is higher than normal.
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Old 01-16-2015, 11:10 PM   #9
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Quote:
Originally Posted by chuckftboy View Post
It may be more of an a/c problem than generator problem. He should check the start and run capacitors. Possibly one of the a/c units has some kind of starting issues
My Onan 5500 will run both a/c's and the refrigerator all day long in 98 degree weather
I agree. My old RV had a 5500 watt and would run 2 AC units, water heater, fridge, TV, and the little things. They have more power than you think and I bet the AC units will pull less amps than people think, once running. Only way to verify amp draw is to use an amp/load meter. Typing on the computer means nothing about amp draw.

I would be looking at fuel filters and air filters first, then as chuckftboy says, AC checking.
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Old 01-17-2015, 01:26 AM   #10
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Two possibilities. First, as already mentioned one of the AC compressors may have starting issues. Start capacitors are cheap, if you know someone that is knowknowledgeable working on electrical systems they can change them. If not take it to a shop. Who ever does it have them install a hard start kit on each compressor. Second, the AC units should have a two minute time delay to prevent the compressor from short cycling. The time delay is to prevent the compressor from starting until the high side and low side pressure have equalized. If the time delay is not working the compressor will draw higher then normal amps at startup.

May 5500kw gas generator runs both AC unit fine. Even in the hot summer traveling on the road.
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Old 01-17-2015, 12:33 PM   #11
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'topdown man', since we know that, "When they are plugged into shore power, there are no issues." At this point, IMO, this is not an AC problem. In addition, "When they try and run both ACs, they will run for a while. Sometimes hours. Then, the generator will bog down and die unless they shut one down."

Bogging down under load can be caused by many factors. Clogged air filter, loose or frayed fan belt and other factors such as low oil level. Since the generator is bogging down, the first place I would look is at the generator air filter, then the belt that drives the generator fan, then the fuel filter. A partially plugged air filter and/or fuel filter and/or loose belt will allow the generator to run under normal low loads, but bog down under high loads. I'm sure your friend has already checked the oil level. All of these as well as low generator oil level can cause high heat and possibly trip the breaker. Since I'm on a roll, how many hours on the generator since it's last maintenance? Hope this in some way helps before looking at AC units.

Good luck.
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