Rear ac

[ahicks]

If both the breakers on the genny are good to go, my bet is the transfer relay was cooked while being switched under load. That's the absolute worst thing you can do to them.

Usually they'll survive that abuse, but they won't do it very often. There's a huge arc across those points when switched under load, and those point will eventually be burnt/pitted to the point where they will no longer pass power efficiently, causing them to heat up and fail completely when under high loads.

[danr62]

All: You guys are awesome. This site is invaluable information for rookies especially! Libero, you were right. A simple breaker switch in the bedroom. I had never even opened all those cabinet doors. I have now!

Again, thanks for all suggestions! Case closed!

[Libero]

Thanks Mel, good point

I believe my 2001 Monaco had ganged breakers on the Onan 7.5 and the OP said he reset "the breaker" so this would imply a ganged arrangement. It was several years ago since I owned that coach and my old mind sometimes gets all the rigs I have had mixed up.

But if the ganged breaker tripped then he would have no power to the coach. But it is always a good idea to check voltage at the AC wall breaker but a simpler method might be to turn the fan on to see if it runs which someone suggested.

Indeed switches, plugs and breakers are my first goto areas and likely suspects if I do not have power at any point. But I first determine if power is supplied to the device before doing anything.

Bottom line is my mind was thinking ganged breaker on the gen. This may not be the case so your comment is indeed helpful. Thanks again for that clarification.

[Libero]

Originally Posted by danr62

All: You guys are awesome. This site is invaluable information for rookies especially! Libero, you were right. A simple breaker switch in the bedroom. I had never even opened all those cabinet doors. I have now!


Again, thanks for all suggestions! Case closed!

Glad you got it case closed and it is good when things are sooo simple. Good object lesson when switching power sources with full AC load attached. The general rule is, don't do it.

Do you want that schematic. You can send me a PM with your email and I can send it in autocad, visio or PDF.

[Brockx]

Originally Posted by wa8yxm

Question is this a 30 amp or a 50 amp rig?

On most 30 amp 2-AC RV's. (And I would guess some 50's) the rear A/C runs through the generator ALL THE TIME, so you may simply have tripped the 20 amp breaker on the genny.

Always trying to learn........

Are you saying the rear air will only run off the gen set?
Both of mine of mine will run off 30 amp shore or Gen set, (refer on gas), is this unusual?

[clyon51]

Originally Posted by Brockx

Always trying to learn........

Are you saying the rear air will only run off the gen set?
Both of mine of mine will run off 30 amp shore or Gen set, (refer on gas), is this unusual?

It depends on the coach. Generally, a 30a coach with 2 ACs, can only run 1 AC on shore power. Some only the front AC, others will have a selector switch to choose one or the other.

In most cases when they have a 5500w genny, the 20a circuit is hard wired to the rear AC, therefore the genny must be running to use both at the same time. If not actually hardwired, it would use an ATS.

On my coach and I assume your's, I have an EMS system that monitors amps on the 4 major circuits and gives them a priority. On shore, once the coach reaches 30a being used, it will cut out one of those circuits off. This is called load sharing. So if I have both ACs running (2 primary circuits) at about 26amps and start the microwave, the EMS will shut power to the micro. If I need the micro, I must shut 1 AC off.

When the genny is running, there is an ATS that transfers the power from the 20a circuit to the rear AC and the 30a circuit powers the rest of the coach. So in essence, I now have 50amps useable in the coach utilizing the full potential of the 50a genny. Of course so would any 30a coach with a 50a genny.

I'm sure there are other minor variations of this, but those are the basics as general info.

[Brockx]

Originally Posted by clyon51

It depends on the coach. Generally, a 30a coach with 2 ACs, can only run 1 AC on shore power. Some only the front AC, others will have a selector switch to choose one or the other.

In most cases when they have a 5500w genny, the 20a circuit is hard wired to the rear AC, therefore the genny must be running to use both at the same time. If not actually hardwired, it would use an ATS.

On my coach and I assume your's, I have an EMS system that monitors amps on the 4 major circuits and gives them a priority. On shore, once the coach reaches 30a being used, it will cut out one of those circuits off. This is called load sharing. So if I have both ACs running (2 primary circuits) at about 26amps and start the microwave, the EMS will shut power to the micro. If I need the micro, I must shut 1 AC off.

When the genny is running, there is an ATS that transfers the power from the 20a circuit to the rear AC and the 30a circuit powers the rest of the coach. So in essence, I now have 50amps useable in the coach utilizing the full potential of the 50a genny. Of course so would any 30a coach with a 50a genny.

I'm sure there are other minor variations of this, but those are the basics as general info.

Thanks for explaining that, this is my first MH.

I have an EMS, first thing it sheds is the rear air if the system sees to much use. It drops the rear compressor, fan continues, I think next in line is fridge goes to gas, never got that far yet, Gen is 5000.

I think if I had a situation on the rear as you described I would have a transfer switch wired in to allow plugging the rear air into a 20amp outlet when camping.

[mel s]

Originally Posted by clyon51

I now have 50amps useable in the coach utilizing the full potential of the 50a genny.

clyon51
50A X 2 = 100A

Because there are 2 120VAC legs/lines from the genset, a "50A coach" actually has 100A to work with when "utilizing the full potential of the 50a genny"......(the same is true if/when the coach is connected to a 50A shore power receptacle)!

Mel
'96 Safari

[clyon51]

Many have done just that. They wire a 20a cord into the rear AC and plug that into the pedistal along with the 30a cord. Some use a manual transfer switch while others use a plug/unplug setup.

[Radarman]

Ahicks has the right idea in my opinion. I still have the original Iota Transfer switch. It is 12 years old now. I have inspected the contacts and checked for terminal tightness--all good. The previous owner must have had the same thoughts also. Just because you can do something doesn't mean it is the best for your equipment. Always try to have only one power source at a time coming into your transfer switch. Always make sure large current draw equipment if off while switching or first hooking up to shore power. If a transfer switch fails, it could be gentle or very bad. Putting 240VAC on a 120VAC circuit will fry things. After transfer switch contacts arc, then pit, then fuse together, very strange things can happen. That is why my Progressive hardwired surge suppressor if AFTER the Transfer switch. It will protect the coach if either power source is bad or if the transfer switch fails.

[clyon51]

Originally Posted by mel stuplich

clyon51
50A X 2 = 100A

Because there are 2 120VAC legs/lines from the genset, a "50A coach" actually has 100A to work with when "utilizing the full potential of the 50a genny"......(the same is true if/when the coach is connected to a 50A shore power receptacle)!

Mel
'96 Safari

Laugh...I know all that Mel. My responce was to Brockx who has a 30a coach, as is mine. With the 50a genny we both have, we can utiilze the full 50a it generates, 30 on one leg and 20 on the other (30 full coach, 20 rear AC). I said nothing about a 50a coach that actually has 100a, but is limited with genny unless it's a 12,000w

[Busyteach]

Originally Posted by mel stuplich

clyon51
50A X 2 = 100A

Because there are 2 120VAC legs/lines from the genset, a "50A coach" actually has 100A to work with when "utilizing the full potential of the 50a genny"......(the same is true if/when the coach is connected to a 50A shore power receptacle)!

Mel
'96 Safari

Actually this is incorrect, although the result is the same. The 50 amp coaches are fed with a 240/120V circuit rather than the conventional 30A 120V circuit. If you will notice all of your shore power breakers are 30 and 50, so they are designed to trip at their respective ratings. A 100 amp load would trip the 50 amp breaker rather quickly. The power supplied from the 50A is exactly the same as that supplied to a house electrical service where you can feed both 120v and 240v circuits.

The error comes from thinking the circuit is 2 120V circuits when in actuality it is a 240V circuit that is split into 2 120V circuits once it enters the coach.

What is really desired is power ( measured in watts or KW ) which is why voltages and current (amps) are raised. Since the power available is the product of voltages x amps it is easy to see why raising either one will raise the power available. If you have a 30 amp 120v circuit you actually have a 3600 watts. If you have a 50 amp 240V circuit you have 12,000 watts or 12KW available. You increase power by raising either voltage or current or both. The current in these circuits are still just 30 and 50 amps respectively. For those who know, I did simplify by assuming no reactive components, power factor of 1, but it is simple and approximate.

I do know that my previous motor home had a load shedding EMS system that shed the front AC if the current draw in the coach got close to 30 amps. It went out me (in 100 degree + weather) and I struggled to find the controller which was accessed by removing the closet floor over the beaker panel. There was a manual test switch on the controller that allowed me to switch back and forth from rear to front air which helped determine the controller was bad.
Since it was proprietary equipment I had no choice but rush order one to me. This system could be defeated but I decided against it since all the wiring was difficult to access and it was a major rats nest. If you have 2 AC units and it does load shedding automatically, there are 2 thermostats, current transformers on the incoming power lines, and a controller they all feed to most likely somewhere hidden so you won't find it easily but usually close to your panel so the CTs will be close.