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Old 08-16-2022, 03:13 PM   #1
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Front and rear Dometic ACs both not working

We have a 2014 XL378 and have an interesting problem. Neither the front or the rear ACs will function while running on the generator. I don't have a 30 amp service at the house, so I do the AC checks with the generator. It also is a good way to exercise the genset.
We were out a couple months ago and both ACs functioned fine for the whole time we were out. Actually, they have never given us any problems.
I brought the Coach home to get ready for our cross-country trip in a couple weeks and now neither of the ACs function. The rear, (bedroom) will run the fan and TRY to run the compressor but after a few seconds it quits trying to run the compressor and the fan stays on. No fuse blows, just tries to run the compressor and cycles about every 20-30 seconds without getting the compressor to run.
The Front AC immediately trips the breaker at the generator, no fan, no nothing, just trips the breaker. Neither AC trips a breaker inside the motorhome. Only the front AC trips one side of the generator.
Not a lot of information, but was hoping I could get some insight before I go up on the roof and start trouble shooting.
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Old 08-16-2022, 05:03 PM   #2
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Far from an expert here.

Have you run the ACs with this generator previously?
Could be a low voltage problem from the generator , plug or receptacle.
Check the voltage at the Breakers in the RV.

If Iím way off base someone will correct me.
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Old 08-16-2022, 05:09 PM   #3
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Originally Posted by leeshearer View Post
Far from an expert here.

Have you run the ACs with this generator previously?
Could be a low voltage problem from the generator , plug or receptacle.
Check the voltage at the Breakers in the RV.

If Iím way off base someone will correct me.
I've run the ACs of the generator many times. I'll get out on the roof in a bit, after it cools down some. (Its 105 outside) My first thought is the fan on the front AC is buggered. It won't run at any position. (Fan only, heat strip) The rear may be a capacitor. I haven't removed the shrouds, so we'll see. if the capacitors are interchangeable, I may swap them around and see what up. I've been looking for some sort of troubleshooting guide but haven't come across anything in the web as of yet.
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Old 08-17-2022, 11:08 AM   #4
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Up on the roof this morning. Checked both ACs for continuity on the fan motors and compressors. Both checked out good on each AC. Which is good, I wasn't going to be thrilled if the compressor(s) were bad. I think I've narrowed it down to the capacitors. Not real comfortable on the correct way to check those without a dedicated capacitor meter. That said, they are inexpensive, (less than the cost of a capacitor tester that hopefully I'd never need again) and both will be here today through Amazon.
Going to be 106 again today, so I may or may not get back up on the roof this afternoon to install.
Stay tuned, fingers crossed!
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Old 08-17-2022, 11:24 AM   #5
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Smile AC's

With units of that age, 8+ years old, and they may have been a year old before being installed on your unit. Fact is, they likely are in need of maintenance.

Coils need to be cleaned, fans need to be checked for proper operation as critters love to build nests in these units, and even the starting capacitors may need to be replaced.

I view all of this as annual maintenance. Doing annual maintenance on anything will likely identify issues, that if otherwise left untouched, will certainly inconvenience one's trips.

Just yesterday I discovered the tape used to seal and connect the AC duct to the ceiling vents had deteriorated. That allowed a lot of cold air to blow into the area between the ceiling and the roof of our TT. It took me a couple of hours to remove the vents, remove the old improper type of tape, apply proper metallic HVAC tape, and clean and reinstall the ceiling vents. NOW we have lots of cold airflow from the vents.

Bob
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Old 08-17-2022, 02:53 PM   #6
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How to test a capacitor

Quote:
Originally Posted by Mooney 78865 View Post
Up on the roof this morning. Checked both ACs for continuity on the fan motors and compressors. Both checked out good on each AC. Which is good, I wasn't going to be thrilled if the compressor(s) were bad. I think I've narrowed it down to the capacitors. Not real comfortable on the correct way to check those without a dedicated capacitor meter. That said, they are inexpensive, (less than the cost of a capacitor tester that hopefully I'd never need again) and both will be here today through Amazon.
Going to be 106 again today, so I may or may not get back up on the roof this afternoon to install.
Stay tuned, fingers crossed!
How to test a capacitor
This is one more trick I should add to "Multimeter 101."
A good capacitor blocks DC. When a DC voltage is applied to it, it draws current for a brief time as it charges to the applied voltage level.

As you may know, when you use your multimeter on any of the ohms (Ω) scales, the meter actually applies voltage to the load through an internal resistor selected by whichever ohms range you have selected. The resistance reported by the multimeter is actually the voltage sensed across the internal resistor within the meter.

If you've ever tested a capacitor with an analog ohmmeter, you would see that the meter immediately displays low resistance and then creeps up to infinity. With a digital ohmmeter or multimeter, you can see something similar.

First, make sure the capacitor is discharged by jumpering across its two terminals--a screwdriver will serve. Then put the ohmmeter on its lowest scale and touch the two probes to the two terminals. On a good capacitor the digits will first show numbers, which will gradually increase to tbe blinking "1" out-of-range state.

Then swap the leads. This reversal of applied polarity will have the effect of discharging the capacitor and then charging it again, to the other polarity. Again you will see the numbers creep up and then go to blinking "1" if it's a good capacitor. You can try this on any of the ohms scales.

A bad capacitor could be conductive (passing DC) in which case the meter will stop at a fixed resistance and not go all the way to blinking "1". Or a bad capacitor could be open, in which case it will always go right to blinking "1".
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Old 08-17-2022, 05:26 PM   #7
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Originally Posted by Larry-NC View Post
How to test a capacitor

This is one more trick I should add to "Multimeter 101."

A good capacitor blocks DC. When a DC voltage is applied to it, it draws current for a brief time as it charges to the applied voltage level.



As you may know, when you use your multimeter on any of the ohms (Ω) scales, the meter actually applies voltage to the load through an internal resistor selected by whichever ohms range you have selected. The resistance reported by the multimeter is actually the voltage sensed across the internal resistor within the meter.



If you've ever tested a capacitor with an analog ohmmeter, you would see that the meter immediately displays low resistance and then creeps up to infinity. With a digital ohmmeter or multimeter, you can see something similar.



First, make sure the capacitor is discharged by jumpering across its two terminals--a screwdriver will serve. Then put the ohmmeter on its lowest scale and touch the two probes to the two terminals. On a good capacitor the digits will first show numbers, which will gradually increase to tbe blinking "1" out-of-range state.



Then swap the leads. This reversal of applied polarity will have the effect of discharging the capacitor and then charging it again, to the other polarity. Again you will see the numbers creep up and then go to blinking "1" if it's a good capacitor. You can try this on any of the ohms scales.



A bad capacitor could be conductive (passing DC) in which case the meter will stop at a fixed resistance and not go all the way to blinking "1". Or a bad capacitor could be open, in which case it will always go right to blinking "1".
Thanks for the detailed response! I'll give that a try.
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Old 08-17-2022, 05:29 PM   #8
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Quote:
Originally Posted by Bob K4TAX View Post
With units of that age, 8+ years old, and they may have been a year old before being installed on your unit. Fact is, they likely are in need of maintenance.



Coils need to be cleaned, fans need to be checked for proper operation as critters love to build nests in these units, and even the starting capacitors may need to be replaced.



I view all of this as annual maintenance. Doing annual maintenance on anything will likely identify issues, that if otherwise left untouched, will certainly inconvenience one's trips.



Just yesterday I discovered the tape used to seal and connect the AC duct to the ceiling vents had deteriorated. That allowed a lot of cold air to blow into the area between the ceiling and the roof of our TT. It took me a couple of hours to remove the vents, remove the old improper type of tape, apply proper metallic HVAC tape, and clean and reinstall the ceiling vents. NOW we have lots of cold airflow from the vents.



Bob
I agree. I'm real good about cleaning the coils annually, along with inspecting the units. I really try to stay up on maintenance and not defer anything. Much easier doing it in front of the house than repairs on the road!
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Old 08-17-2022, 06:04 PM   #9
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You might consider putting soft start units on you A/C units. The inrush start up current will be much lower than normal. This would be easier on your genset also.
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Old 08-17-2022, 06:58 PM   #10
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Originally Posted by KRedburn View Post
You might consider putting soft start units on you A/C units. The inrush start up current will be much lower than normal. This would be easier on your genset also.
I've been looking into them. Really didn't know it was a thing until this issue came up.
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Old 08-18-2022, 10:04 AM   #11
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So, the Amazon Doodle didn't show up until after dark last night, which put me off to this morning for the install of the two capacitors.
As I mentioned earlier, they are not identical, (to be expected as the ACs aren't identical) and only one had embossed markings as to wiring layout. After a bit of studying, the wiring locations were straight forward. Each capacitor has three terminal posts, one has 4 spade connections, one has 3, and the final has 2. 4 spades were control, 3 spades were HERM, and the 2 spade was fan. Sizes were a bit different, so I had to adjust the mounting straps for both capacitors.
Scratching my head on the layout and the actual install for both capacitors took maybe 45 minutes.
Then went inside with fingers crossed, THEY BOTH WORK!!
Ran both for maybe 10 minutes each, nice and cold! Happy, happy, joy, joy!
Total price for both capacitors was less than $50 with free same day delivery from Amazon.
So, to recap the issues:
Rear AC would run the fan and try to start the compressor, then the compressor would stop trying to start. This would repeat until I shut the unit off. The fan never stopped, and it never tripped the breaker.
The front AC would try to start, (hum) then trip the breaker.
I learned a lot about the start and run functions of air conditioners over the last couple days, more than I wanted! Both ACs had different symptoms but the same common part failure. Good to know I guess. Just wish it wasn't 105 outside!
I'd also like to know why both decided to go south at the same time... but I'll take the win on getting them fixed without calling in a tech.
And a final note. Both ACs start MUCH softer than before, I can run each unit from a 20-amp breaker from the house without tripping it. That's never been the case before.
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Old 08-18-2022, 10:19 AM   #12
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Smile Good News

GREAT on getting them repaired and especially a DIY not having to pay big bucks to the camper service department.

Hypothetically, the units have been exposed to the same environment for the same number of years. Capacitors are all basically made the same way and of the same materials. The heat, electrically generated and atmosphericly will cause them to dry on the inside. This causes the capacitance value to deteriorate or decrease and thus it no longer functions as designed.

Inexpensive and effective repair is to replace them. Now you are likely good for another 5 to 10 years.

Bob
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Old 08-18-2022, 10:40 AM   #13
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2 thoughts

Quote:
Originally Posted by Mooney 78865 View Post
As I mentioned earlier, they are not identical, (to be expected as the ACs aren't identical) and only one had embossed markings as to wiring layout. After a bit of studying, the wiring locations were straight forward. Each capacitor has three terminal posts, one has 4 spade connections, one has 3, and the final has 2. 4 spades were control, 3 spades were HERM, and the 2 spade was fan. Sizes were a bit different, so I had to adjust the mounting straps for both capacitors.
After doing this once or twice, you learn to not only match the capacitance and voltage but also the physical size. If the manufacturer could get a capacitor that size, you can too.
Quote:
Originally Posted by Mooney 78865 View Post
I learned a lot about the start and run functions of air conditioners over the last couple days, more than I wanted! Both ACs had different symptoms but the same common part failure. Good to know I guess. Just wish it wasn't 105 outside!
I'd also like to know why both decided to go south at the same time... but I'll take the win on getting them fixed without calling in a tech.
As Bob (K4TAX) mentioned, electrolytic capacitors contain a gel (fluid) separating the internal electrodes (a spool of Mylar and foil). Heat is the enemy--it dries out the fluid and the capacitor no longer functions. When restoring old radios or guitar amps (or automotive computers), the first thing to do is replace all the electrolytic capacitors.
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Old 08-18-2022, 10:49 AM   #14
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Quote:
Originally Posted by Mooney 78865 View Post
I've run the ACs of the generator many times. I'll get out on the roof in a bit, after it cools down some. (Its 105 outside) My first thought is the fan on the front AC is buggered. It won't run at any position. (Fan only, heat strip) The rear may be a capacitor. I haven't removed the shrouds, so we'll see. if the capacitors are interchangeable, I may swap them around and see what up. I've been looking for some sort of troubleshooting guide but haven't come across anything in the web as of yet.
Your first thought should be check what voltage (MULTI METER) is getting sent to a/c rule out that generator may be at fault

EDIT....

deleted the rest as a lot of other people put good advise up while I was two finger typing
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Old 08-18-2022, 01:19 PM   #15
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Quote:
Originally Posted by Bob K4TAX View Post
GREAT on getting them repaired and especially a DIY not having to pay big bucks to the camper service department.

Hypothetically, the units have been exposed to the same environment for the same number of years. Capacitors are all basically made the same way and of the same materials. The heat, electrically generated and atmosphericly will cause them to dry on the inside. This causes the capacitance value to deteriorate or decrease and thus it no longer functions as designed.

Inexpensive and effective repair is to replace them. Now you are likely good for another 5 to 10 years.

Bob
Very happy not having to get a Tech involved, and the wait times.
Your explanation makes sense, God Knows we are exposed to prolong periods of high outside temps here in the Central Valley. Generally, we use both ACs pretty often. This year though we've only been out in May. That's all about to change after Labor Day. Heading back east for a 4-6 weeks.
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Old 08-18-2022, 01:24 PM   #16
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Originally Posted by Larry-NC View Post
After doing this once or twice, you learn to not only match the capacitance and voltage but also the physical size. If the manufacturer could get a capacitor that size, you can too.

As Bob (K4TAX) mentioned, electrolytic capacitors contain a gel (fluid) separating the internal electrodes (a spool of Mylar and foil). Heat is the enemy--it dries out the fluid and the capacitor no longer functions. When restoring old radios or guitar amps (or automotive computers), the first thing to do is replace all the electrolytic capacitors.
I really didn't think too much about size figuring the capacitance would pretty much dictate it. Both of the new ones were slightly larger diameter with the same height. Wasn't a big deal, they are held in place with "plumbers" tape, so it was massaging the tape to another hole. Both fit fine in their respective enclosures.
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Old 08-25-2022, 07:33 PM   #17
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Quote:
Originally Posted by Mooney 78865 View Post
We have a 2014 XL378 and have an interesting problem. Neither the front or the rear ACs will function while running on the generator. I don't have a 30 amp service at the house, so I do the AC checks with the generator. It also is a good way to exercise the genset.
We were out a couple months ago and both ACs functioned fine for the whole time we were out. Actually, they have never given us any problems.
I brought the Coach home to get ready for our cross-country trip in a couple weeks and now neither of the ACs function. The rear, (bedroom) will run the fan and TRY to run the compressor but after a few seconds it quits trying to run the compressor and the fan stays on. No fuse blows, just tries to run the compressor and cycles about every 20-30 seconds without getting the compressor to run.
The Front AC immediately trips the breaker at the generator, no fan, no nothing, just trips the breaker. Neither AC trips a breaker inside the motorhome. Only the front AC trips one side of the generator.
Not a lot of information, but was hoping I could get some insight before I go up on the roof and start trouble shooting.
I assume that this generator has run the ACís in the past? What size generator? How did you run the ACís when you were out?

I would go someplace and hookup to a 50amp service and check the ACís. If they are working hooked up, itís probably a gen problem.
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Old 08-25-2022, 07:42 PM   #18
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AC's on Generator

There are 3 things every generator should have, although most have none of these.

Those are:
VOLTMETER - this shows the output voltage of the generator.
AMPMETER - this shows the current output of the generator.
FREQUENCY METER - this shows the output frequency of the generator.

With these three, you can easily determine at a glance if the generator is doing its job correctly as it should. No extra equipment is needed.

Bob
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