A/C operation

Topic: A/C operation (Read 783 times) previous topic - next topic

A/C operation

May 23, 2024, 10:16:16 am

Hello Forum, yesterday while at coach, we replaced the old Duo therm 5 button thermostat with the new Micro air easy touch. Easy replacement. Plug and play. We tested it by running it thru all zone's on cool and heat. Works great. Had generator running to test as I only have 20 amp available at storage.
The previous owner of this coach replaced the generator with a 8k Onan/Cummins. While testing the running of the AC zones, we could run one AC with no problem, but when second would start up, they would run a few seconds then shutdown. I thought maybe the new thermostat might have something to do with this, so I plugged the old one back in, same thing. We've owned this coach for about 6 months and have never tried to run both AC on generator. As far as I can tell, the AC's are both Duotherm 13.5s. We have run both but been plugged in to 50 amp and it was fine. We also have a residential fridge that pulls a couple amps. Just thought I'd give all the info I know.
Anyway, I know that's a lot, but my questions are: Shouldn't the Onan have all the power necessary to run both. Our previous coach, had a 10k and it was never an issue. How would I be able to tell the generator is putting out its available power? Would installing soft starts on the AC's help with this. What are some things to check?
Thanks in advance for reading this long post if you did...

Re: A/C operation

Reply #1 – May 23, 2024, 10:26:02 am

Did you run the one that shut down by its self.

Re: A/C operation

Reply #2 – May 23, 2024, 10:29:06 am

Both shutdown. Either will run independently for at least 20 minutes. That's as long as we tried while experimenting.

Re: A/C operation

Reply #3 – May 23, 2024, 10:52:36 am

My brothers 8k Onan runs both his airs on his Monaco 40' but he still has original fridge. What does your voltage show when the air fails? Maybe just needs adjustment on the generator.

Re: A/C operation

Reply #4 – May 23, 2024, 11:00:17 am

I will watch voltage meter when we try again. Is generator adjustment something I can do? I'll look at manual.

Re: A/C operation

Reply #5 – May 23, 2024, 11:00:33 am

Since you don't mention any circuit breakers tripping, I will assume that your A/C units are shutting down due to seeing low voltage/amperage on their power supply.

I'm not by any definition an electrical expert, but my armchair guess is that your 8 kW generator should be able to handle 2 A/C units, ASSUMING that it is putting out the advertised rated power. I think you would need a digital multimeter with a clamp-on ammeter to check the generator output.

About the soft start question. We have a Micro-Air EasyStart on our residential 4-ton heat pump. It reduced the LRA (lock rotor amps) from 109A to 30A. The LRA is the big spike in amps (inrush current) that happens when the compressor motor turns on. It only lasts for a few milliseconds, and then the compressor settles down to its running amp draw which is a lot lower.

SO, if your problem is being caused by the LRA spike from the second A/C overloading the generator, then a soft start might help.

Re: A/C operation

Reply #6 – May 23, 2024, 11:08:19 am

I will try and find a way to check generator output to see if it's doing as advertised. I was thinking about soft starts prior this coming up, just to be easier on equipment. They probably would not be a bad add for our heat pumps at home also. We have a 4 ton on the house, and a heat pump for the pool also. Granted the heat pump on the pool is only used a couple months. We are in Phoenix , AZ area...

Re: A/C operation

Reply #7 – May 23, 2024, 11:13:31 am

When the generator was changed out to an 8kw did they remove the remote radiator?

Reason being is the math that follows
2 A/C units @ 14amps
1 inverter/converter @ 3amps
1 refer @ 5ams
1 remote radiator fan at 4.5 to 4.9amps
Run time with this load not long

You need to check the amps on each leg with an amp meter not a volt meter

Mike

Re: A/C operation

Reply #8 – May 23, 2024, 11:15:15 am

Quote from: Bigoil76 – May 23, 2024, 11:08:19 am

They probably would not be a bad add for our heat pumps at home also. We have a 4 ton on the house...We are in Phoenix , AZ

Don't want to sidetrack this thread, but I DEFINITELY recommend a soft start on your residential heat pump, assuming it is NOT one of the newer inverter driven models (which have soft start built in). Soft starts make life easier for any type of motor driven compressor. Easier on the motor, easier on the compressor, easier on your ears (quieter startup).

Re: A/C operation

Reply #9 – May 23, 2024, 11:47:55 am

Mike, you raise a question I cannot answer about the removal of the radiator. I would think so, but will check. And yes , Amps check...thanks

Chuck, thanks for the input. Are soft starts easy to install? Even for an electrical dummy like myself. It looks like they are.

Re: A/C operation

Reply #10 – May 23, 2024, 12:06:08 pm

Quote from: Bigoil76 – May 23, 2024, 11:47:55 am

Chuck, thanks for the input. Are soft starts easy to install? Even for an electrical dummy like myself. It looks like they are.

I gotta run to town with the DW, but I'll send you a PM later today telling you everything I know about soft starts. It won't be a long note.

Re: A/C operation

Reply #11 – May 23, 2024, 02:07:27 pm

Onan web site says the 8KW RV generator can run two 15,000 BTU AC with power to spare. Running amps of 66.6 Mike's total only comes up to 41 amps. So there is plenty to spare.

When the AC's shut down, does the rest of the power go off from the generator? Or, do just the AC's top running.
What do you do to get 1 AC to start back up?

If you don't know when the fuel and air filter has been changed, Might do that now.

If the generator shuts down, Have you looked to see if it threw a error code?

One of the spec sheets says Double pole 35A breaker. Maybe loads not balanced on phases?

Re: A/C operation

Reply #12 – May 23, 2024, 02:34:54 pm

TurboJack: yes, I thought the 8k should have more than enough to run most things..When the AC's shutdown , just the AC's would stop. Fridge would not bobble. If we waited about five minutes and touched nothing, one of the AC 's would start, then a couple minutes later the other, and then within a about 15 seconds, both would stop, if I shut one zone off, or raise desired temperature, one AC would start and would run as long as desired. I do not know when the generator was serviced last. I will look through the records I have. Now would probably be a good time to get that service if needed. Thanks....

Re: A/C operation

Reply #13 – May 23, 2024, 02:55:11 pm

Quote from: Bigoil76 – May 23, 2024, 02:34:54 pm

TurboJack: yes, I thought the 8k should have more than enough to run most things..When the AC's shutdown , just the AC's would stop. Fridge would not bobble.

Is the (residential) fridge plugged into the shore/generator-only outlet or is it plugged into the one that also is powered by the inverter (or is there a dedicated inverter for the fridge)?

Re: A/C operation

Reply #14 – May 23, 2024, 06:10:57 pm

I still have the old Dometic Penguin 2's on my rig, and when you watch the amp load, they take around 25 amps to start and 14ish running. If you're running one at 14ish amps, plus the fridge, starting the second may be too much for an 8k. Soft starts may be the ticket.

Re: A/C operation

Reply #15 – May 23, 2024, 06:25:31 pm

My 78 Vogue had a 6.5 Onan air cooled gen. and would run two 13.5 a/c's in 100 Deg. temps.

Re: A/C operation

Reply #16 – May 23, 2024, 06:45:21 pm

Michelle, it is plugged into the inverter powered plug. The fridge runs while boondocking, then we run the generator for a couple hours in morning, and a couple hours at night to keep batteries up. There is no dedicated inverter for refrigerator.

Re: A/C operation

Reply #17 – May 23, 2024, 07:13:47 pm

I wonder if both of the ac's are running on only one leg of the generator. I was working on a coach at the dealership many years ago and it had a 6.5 Onan. It would only run one ac. I checked everything I could think of and finally found the problem. The engine block heater was turned on. We were in Florida in the summer, so it should not have been turned on. Turned it off and then both ac's ran on the 6.5. I would check that the new generator is wired correctly

Re: A/C operation

Reply #18 – May 23, 2024, 09:01:24 pm

Quote from: Bigoil76 – May 23, 2024, 06:45:21 pm

Michelle, it is plugged into the inverter powered plug. The fridge runs while boondocking, then we run the generator for a couple hours in morning, and a couple hours at night to keep batteries up. There is no dedicated inverter for refrigerator.

That could be why the fridge didn't bobble - perhaps the inverter continued to power it.

Re: A/C operation

Reply #19 – May 23, 2024, 11:02:39 pm

Hey Keith, what inverter is in your new rig? I know some of the Victrons will pull power from the batteries if the load demand exceeds the capacity of the gen/shore power. Maybe it's just not turned on and could help your situation?

Re: A/C operation

Reply #20 – May 24, 2024, 12:26:57 am

Keith, I'll have to look to be sure. I think it said Xantrex.....almost positive not Victron.

Re: A/C operation

Reply #21 – May 24, 2024, 01:40:43 am

Quote from: WS6_Keith – May 23, 2024, 11:02:39 pm

Hey Keith, what inverter is in your new rig? I know some of the Victrons will pull power from the batteries if the load demand exceeds the capacity of the gen/shore power. Maybe it's just not turned on and could help your situation?

Our Magnum 3012 hybrid is supposed to do that, not sure if it does though.

Re: A/C operation

Reply #22 – May 24, 2024, 09:02:29 am

Do you feel the generator struggles while 2nd AC is trying to start until the AC shut down? Does the 2nd AC start before shutting down, or never gets started?

Re: A/C operation

Reply #23 – May 24, 2024, 09:08:08 am

With inverter and refrigerator turned off, plug fan or lamp with old style incandescent bulb into an outlet, then try test again. I am curious what will happen

Re: A/C operation

Reply #24 – May 24, 2024, 01:31:23 pm

Keith, the Micro-Air Easy-Starts aren't true "plug and play", and not what I'd consider "easy" installs, however, I'm an electron idiot and did both a/c's in one day. You will need to get on the roof and access the innards of the Dometics and run a wire bundle to the Easy-Start module to the Dometic controller. I can now run either unit off a 2000watt Honda generator and can run both units off a 30amp outlet as long as NOTHING else is energized.

Quote from: Bigoil76 – May 23, 2024, 11:47:55 am

Chuck, thanks for the input. Are soft starts easy to install? Even for an electrical dummy like myself. It looks like they are.

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