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Old 04-15-2021, 05:41 PM   #1
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2012 Interstate Coach
Los Gatos , California
Join Date: May 2012
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Dometic AC Unit drawing excessive power on startup

Hello Everyone,

I have a 2012 Airstream Interstate EXT that I am prepping for a trip. All of the systems are working fine, except for the AC.

Ive tried shore power and the generator, it starts up, but when the compressor kicks in, it shuts everything down. FWIW, the AC has not been run for about 2 years.

SEQUENCE
Start Generator
Await the 'Power Center' to queue up the available loads (W/H, Micro, AC, etc)
Turn on AC @ the Thermostat
After a brief pause, the AC turns on and pulls about 8 Amps.
After another brief pause the compressor (I believe) kicks on and pulls an additional 15 Amps or so (the display is reading 23- 24 Amps). That lasts for a second or two, them the Power Center sheds the loads.

The AC has run before many times in the past powered from the generator. I know that when the compressor kicks in, there is a brief surge in power consumption. For some reason, this surge now seems more that it was in the past.

DETAILS
Generator - Cummins Onan 2500LP
AC - Dometic (not sure of the model #, however it is a 13.5 BTU that came standard on the unit.

I was hoping that maybe the unit needed a little cycling to help loosen things up after sitting awhile (I'm a mechanical guy), however after multiple attempts, it still will not operate.

I plan on pulling the AC shroud tomorrow and looking around. Any suggestions as to what my issue may be?
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Old 04-15-2021, 06:06 PM   #2
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2011 Interstate Coach
Evansville , Indiana
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I’m following this thread. We have a 2011 and it has been doing the exact same thing ever since I installed a Microair EasyStart. I have a Yamaha inverter genset that I use for tailgating and I got the soft start so I could run the AC if needed. That goal was achieved but now the AC kicks out with the Onan genset. Not sure what’s going on.
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Old 04-15-2021, 06:25 PM   #3
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2017 25' International
West Lake Hills , Texas
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How do you know itís the AC?
Have you measured the starting amperage draw?
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Old 04-15-2021, 06:28 PM   #4
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Townsend , Tennessee
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I had exactly the same issue with my 2013. I guess the compressor draws more current as it gets older. I installed an EasyStart from Microair and the problem vanished. The inrush current is a lot lower and no longer trips the system.
The installation is straightforward from the included instructions.
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Old 04-16-2021, 10:22 AM   #5
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2019 25' Flying Cloud
Lakewood , New Mexico
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If you do not want to install a soft start, test your capacitors and if one is bad or out of specs, replace all of them. I replace mine as soon as they NEAR out of tolerance. I test mine every two to three years. I've seen several AC's replaced when they only needed new capacitors. One of the tricks is to catch a bad capacitor before it can adversely affect a compressor or motor.
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Old 04-16-2021, 11:20 AM   #6
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2019 23' Flying Cloud
Waterford , New York
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Check your cords, connectors, circuit breakers and wiring. Eight amps before the compressor comes
On sounds excessive. What is the voltage
When the unit is running. If we donít know the voltage we really donít know how much power the system is using.
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Old 04-16-2021, 01:04 PM   #7
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Fulton , Maryland
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Quote:
Originally Posted by BigTexRex View Post
If you do not want to install a soft start, test your capacitors and if one is bad or out of specs, replace all of them. I replace mine as soon as they NEAR out of tolerance. I test mine every two to three years. I've seen several AC's replaced when they only needed new capacitors. One of the tricks is to catch a bad capacitor before it can adversely affect a compressor or motor.
I think this is good advice. My 2013 Interstate air conditioner (A/C) is also exhibiting the increased current draw such that I can no longer will run off the generator. I've done a lot of work and research on this problem. The A/C runs OK with shore power. I added the MicroAir Easy-Start and the A/C starts easier on shore power, but still will not run on generator. I finally was able to get the A/C to run from generator by tripping the 120VAC circuit breaker that caused the Precision Circuits Power Control System (aka Mini-PCS) to shut down. I think it was the water heater CB, but I'm not near my van now. I've concluded that the aged A/C unit now draws more that the GEN setting on the Power Control System allow. That limit was 20A on the older Mini-PCS Model 600, but was increased to 22A on the newer Model 610 units.

My CB shut down work around is only a temporary fix. Now I need to check and replace the capacitors on my 9 year old A/C unit.

I'm attaching a couple of Precision Circuits documents for reference.
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Old 04-16-2021, 02:14 PM   #8
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1987 32' Excella
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My power converter draws about 8 amps when the batteries are moderately discharged.

When you say you tried it on shore power. Is that a proper 30 amp circuit or did you try it on a 20 amp circuit?
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Old 04-16-2021, 05:49 PM   #9
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2009 27' FB Classic
Sioux Falls , South Dakota
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Four things to look at:
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Old 04-16-2021, 06:04 PM   #10
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2009 27' FB Classic
Sioux Falls , South Dakota
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Four things to look at:
1. Voltage of generator falls below 108 Volts under starting load Generator too small

2. Outdoor coil is very dirty or blocked with debris/ cottonwood. Clean outdoor coil with approved coil cleaner

3. The outdoor ambient is above 90 degrees. Try when temp fall to 80 degrees

4. The t'stat has failed and the 4-5 minute time delay from shutdown to start has failed. Turn unit off wait 10 minutes then turn unit on. If it starts replace t'stat

5. The unit is overcharged. On these small units this is very possible. Call service tech to recharge unit to proper charge. A wrong charge of 1 oz. could cause this problem

6. Dirt inside system has reduced the small port in the expansion valve that allows for the slow equilization between the high and low side of the refrigeration system. Replace expansion valve.


Nothing wrong with compressor. Compressors either work or they don't nothing in between. Good Luck and happy streaming
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Old 04-16-2021, 06:17 PM   #11
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2020 23' Flying Cloud
Sebastian , Florida
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Wow, lots of great information! I will humbly submit that 15 A inrush does not seem excessive, based on playing around with a power monitor before and after having a microaire installed on the 13.5 Dometic on my 23 FB.
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Old 04-16-2021, 07:03 PM   #12
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Fulton , Maryland
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All good suggestions but this problem is on Interstate Sprinter Vans with built in Onan LP generators and the Precision Circuits Power Control System Mini-PCS. The Mini-PCS is a load sheading device that senses when on generator power.

The problem that OP-kaylorsan experienced has little to do with compressor. The problem is the electrical load sheading controls on these vans will cut the power when compressor starts.

Quote:
Originally Posted by gr.austin View Post
Four things to look at:
1. Voltage of generator falls below 108 Volts under starting load Generator too small

2. Outdoor coil is very dirty or blocked with debris/ cottonwood. Clean outdoor coil with approved coil cleaner

3. The outdoor ambient is above 90 degrees. Try when temp fall to 80 degrees

4. The t'stat has failed and the 4-5 minute time delay from shutdown to start has failed. Turn unit off wait 10 minutes then turn unit on. If it starts replace t'stat

5. The unit is overcharged. On these small units this is very possible. Call service tech to recharge unit to proper charge. A wrong charge of 1 oz. could cause this problem

6. Dirt inside system has reduced the small port in the expansion valve that allows for the slow equilization between the high and low side of the refrigeration system. Replace expansion valve.

Nothing wrong with compressor. Compressors either work or they don't nothing in between. Good Luck and happy streaming
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Old 04-16-2021, 08:31 PM   #13
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Lake Mary , Florida
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First thing you check is capacitors. Make sure you learn how to test and discharge capacitors before you tackle this yourself

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Old 04-17-2021, 07:51 AM   #14
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Or . . . consider a newer quiet Coleman NDQ (although I hear they can be in short supply). Not only will a new ac draw less amps at startup, the NDQ will only draw 8 to 9 amps while running, and finally, it is probably at least 4-7 decibels more quiet. It will be nice to carry on conversations at normal speech volumes.
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Old 04-17-2021, 09:37 AM   #15
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Yep, I’ve been thinking of replacing the Dometic with a quieter AC like the Coleman or RecPro. Combine that with the new quieter Onan genset inverter and I’d be the envy of the Interstate boondocking rally! Not sure why it took Onan so long to come out of the Dark Ages. I’ve always wondered why Honda and Yamaha didn’t enter the RV market with their exceptionally quiet and reliable inverters. Onan would be toast.
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Old 04-17-2021, 04:22 PM   #16
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I had another reason to add the soft start....my AI is configured with the option to run the AC with the inverter (a 3000watt Magnum Hybrid). Before the soft start was added, whenever the compressor started I would get a momentary over current spike out of the inverter. While this was still within ďacceptableĒ limits, for duration, I did not want to stick my head in the sand with this one. Now I see no over current spikes. The inverter is happy.
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Old 04-25-2021, 09:39 AM   #17
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Los Gatos , California
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UPDATE
I’ll provide more details later, however the problem seems to be with the fan motor. I spent a lot of time on the phone and on the roof trying to diagnose the issue. What I found is that the fan motor was not spinning on startup. It was drawing 8 amps, but never turning. The additional amp draw from the compressor indeed put me over the limit, however the root cause (we believe) is the motor. The motor spins freely and smoothly when not energized. However, once power is supplied it locks up. I was able to manually ‘start’ the motor spinning from the locked up condition and then was able to get the compressor running. The system ran fine for a few minutes then shut down again. The fan never felt like it was above low speed.

I have a replacement motor on order and should get it installed later this week. I’ll provide an update at that time.

As always, this group is a valuable resource and I appreciate the time and effort that members take to make it so.
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Old 04-25-2021, 02:18 PM   #18
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St. Augustine , Florida
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Capacitors can knock the crap out of you if your not careful or don't know what you are doing. Whan in doubt, let the RV place fix it.
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Old 04-25-2021, 07:43 PM   #19
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2014 Interstate Ext. Coach
Evans , GA
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Knowing that we would spend around 9 days in our inlaws driveway on 15 AMP power, and possibly wind up sleeping in our coach, I installed a MicroAir Easy Start 364. After installing and "programming" the unit, it easily starts up our AC. Power draw dropped to 11-12 AMPS during startup. I plan on purchasing a Champion Dualfuel 2500 generator to use instead of the loud Onan that sits underneath. Easy start also made the compressor starts a lot quieter as well.
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Old 05-08-2021, 10:29 PM   #20
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2012 Interstate Coach
Los Gatos , California
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PROBLEM SOLVED

Third timeís a charm...

I installed a softstart unit. No go. ~$300

During that install, noticed that the motor was locked up when under load. Changed it out. No go. ~ $180 on eBay.

The only real item left was the starting capacitor. Changed it out. Did the trick. ~ $20 on eBay.

FWIW, used BRBARNZ wrote me right after I purchased the motor and suggested it was the capacitor; he was indeed correct.

In any case, I have a new motor and a nice soft start up. Hopefully Iím good to go for awhile.

Thanks again for everyoneís help.
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