Generator Won't Run Both A/C Units

[BrianB]

I have two roof A/C units. They are operated by two separate thermostats.

I have an Onan LP generator 6500 50AMP.

I can run the A/C units separately on shore power (120V)

Both units will not run on the generator. The generator has two circuit breakers on it and they are both on and functioning.

[wolfe10]

Welcome to the FMCA Forum.

If you have 50 amp coach electrical service, do all other appliances work-- i.e. are both sides of your 50 amp box hot?

If not and if you are safe working around 120 VAC, check for power in and out of the ATS (Automatic Transfer Switch) while on generator power.

Brett

[Guest BillAdams]

You mention that you can run both A/C separately on 120 but you don't say it you can run both simultaneously. You also don't say if both A/C units operate separately (properly) while on the genset.

[BrianB]

You mention that you can run both A/C separately on 120 but you don't say it you can run both simultaneously. You also don't say if both A/C units operate separately (properly) while on the genset.

Brett: Yes all other appliances work. (micro) and I have 125V at the outlets while the gen is running.

Bill: Yes I can run both A/C's at the same time while on 120V shore power.

While on shore power the A/C units will start up when the switch is turned on. When on generator power there is a long delay before they will start even if the gen has been running for some time.

[rrlowther]

Brett: Yes all other appliances work. (micro) and I have 125V at the outlets while the gen is running.

Bill: Yes I can run both A/C's at the same time while on 120V shore power.

While on shore power the A/C units will start up when the switch is turned on. When on generator power there is a long delay before they will start even if the gen has been running for some time.

We just went through this same issue. Although our dealer where we purchased the coach told us that the generator won't not run both a/c's. Well, I researched it and figured out that was nonsense. I took our coach to another service center and explained the problem.

While on the generator we could turn the front A/C on and run it with no issue. When we turned on the back A/C it would immediately kill the front a/c.

What we found out was that the back a/c is bad. That's why it wouldn't run both. This was after we spent several hundred dollars having the generator checked out. But at least now we know. Thank goodness for the warranty.

[BrianB]

Thanks for the reply. Both units run properly. Each will go on and cool with two fan speeds available.

They just won't run at the same time on the gen.

Rear will not run on the generator at all.

[BrianB]

I opened the power panel and I have power on the black line BUT no power on the red line?

What next? Does this panel get power from the genset or from the transfer switch?

[wolfe10]

Brian,

Difficult to tell from that photo, but with 50 amp service, my next step would be to (ASSUMING YOU ARE SAFE WORKING AROUND 120/240 VAC) to open the ATS (Automatic Transfer Switch) and with shore power and generator off check all connections. Then start the generator and check for power IN and OUT.

Brett

[BrianB]

Brian,

Difficult to tell from that photo, but with 50 amp service, my next step would be to (ASSUMING YOU ARE SAFE WORKING AROUND 120/240 VAC) to open the ATS (Automatic Transfer Switch) and with shore power and generator off check all connections. Then start the generator and check for power IN and OUT.

Brett

Thanks Brett, It looks like to access the ATS I have to remove the converter. Is there another way to access this?

[wolfe10]

Thanks Brett, It looks like to access the ATS I have to remove the converter. Is there another way to access this?

Brian,

Sorry, I don't know where the ATS is on your coach. On ours and many others it is easy to access without removing anything else.

Brett

[BrianB]

I found a J-box under the passenger foot area where the generator output connects to the wires to the rear of the coach. I started the Onan and I again have power on the black leg but there is no power on the red leg. The red is probably the 20Amp leg and is why the rear A/C has no power when on the generator. The ATS while on shore power gives it to both legs in the panel I posted. But on generator it divides the power into 30 and 20 amp legs and since there is no 20 amp leg from the generator there is no power in the panel on the red 20 amp wire.

Now to find out why the generator has no 20AMP output. Any ideas?

[wolfe10]

Now to find out why the generator has no 20AMP output. Any ideas?

Start by checking all connections between generator and ATS/junction box. Loose wire connections are not that uncommon. Wire nuts are cheap!

Brett

[rrlowther]

Thanks for the reply. Both units run properly. Each will go on and cool with two fan speeds available.

They just won't run at the same time on the gen.

Rear will not run on the generator at all.

Ours back a/c worked. It would run, but the heatpump was drawing way more power then it needed. But it sounds like you are on the right trail with check power in and out.

[BrianB]

Start by checking all connections between generator and ATS/junction box. Loose wire connections are not that uncommon. Wire nuts are cheap!

Brett

The J-box is right over the generator. The generator is right under the passenger seat.

I will have to lower the generator to see further upstream.

Is there any reason for the one leg to fail? Circuit board etc?

[F176784]

Brian:

You said the 2 circuit breakers on the gen set are operating? Have you checked the output voltage at the circuit breaker to make sure it isn't open? It is probably the 20 amp breaker that powers the rear air. I would try turning the breakers off and back on at the gen set and if that doesn't work check the voltage at the breaker.

Mike V